Transmission of Mycobacterium tuberculosis is a recognized risk in health care facilities. The magnitude of the risk to HCWs varies considerably by the type of health care facility, the prevalence of TB in the community, the patient population served, the HCW’s occupational group, the area of the health care facility in which the HCW works and the effectiveness of TB infection-control interventions. The risk may be higher in areas where patients with TB are provided care before diagnosis and initiation of TB treatment and isolation precautions (e.g., in clinic waiting areas and emergency departments) or where diagnostic or treatment procedures that stimulate coughing are performed. Nosocomial transmission of M. tuberculosis has been associated with close contact with persons who have infectious TB and with the performance of certain procedures (e.g., bronchoscopy, endotracheal intubation and suctioning, open abscess irrigation and autopsy). Sputum induction and aerosol treatments that induce coughing may also increase the potential for transmission of M. tuberculosis. Personnel in health care facilities should be particularly alert to the need for preventing transmission of M. tuberculosis in those facilities in which immunocompromised persons (e.g., HIV-infected persons) work or receive care—especially if cough-inducing procedures, such as sputum induction and aerosolized pentamidine treatments, are being performed.

Transmission and Pathogenesis

M. tuberculosis is carried in airborne particles, or droplet nuclei, that can be generated when persons who have pulmonary or laryngeal TB sneeze, cough, speak or sing. The particles are an estimated 1 to 5 μm in size and normal air currents can keep them airborne for prolonged time periods and spread them throughout a room or building. Infection occurs when a susceptible person inhales droplet nuclei containing M. tuberculosis and these droplet nuclei traverse the mouth or nasal passages, upper respiratory tract and bronchi to reach the alveoli of the lungs. Once in the alveoli, the organisms are taken up by alveolar macrophages and spread throughout the body. Usually within two to ten weeks after initial infection with M. tuberculosis, the immune response limits further multiplication and spread of the tubercle bacilli; however, some of the bacilli remain dormant and viable for many years. This condition is referred to as latent TB infection. Persons with latent TB infection usually have positive purified protein derivative (PPD)-tuberculin skin-test results, but they do not have symptoms of active TB, and they are not infectious.

In general, persons who become infected with M. tuberculosis have approximately a 10% risk for developing active TB during their lifetimes. This risk is greatest during the first two years after infection. Immunocompromised persons have a greater risk for the progression of latent TB infection to active TB disease; HIV infection is the strongest known risk factor for this progression. Persons with latent TB infection who become co-infected with HIV have approximately an 8 to 10% risk per year for developing active TB. HIV-infected persons who are already severely immunosuppressed and who become newly infected with M. tuberculosis have an even greater risk for developing active TB.

The probability that a person who is exposed to M. tuberculosis will become infected depends primarily on the concentration of infectious droplet nuclei in the air and the duration of exposure. Characteristics of the TB patient that enhance transmission include:

• disease in the lungs, airways or larynx

• presence of cough or other forceful expiratory measures

• presence of acid-fast bacilli (AFB) in the sputum

• failure of the patient to cover the mouth and nose when coughing or sneezing

• presence of cavitation on chest radiograph

• inappropriate or short duration of chemotherapy

• administration of procedures that can induce coughing or cause aerosolization of M. tuberculosis (e.g., sputum induction).

Environmental factors that enhance the likelihood of transmission include:

• exposure in relatively small, enclosed spaces

• inadequate local or general ventilation that results in insufficient dilution and/or removal of infectious droplet nuclei

• recirculation of air containing infectious droplet nuclei.

Characteristics of the persons exposed to M. tuberculosis that may affect the risk for becoming infected are not as well defined. In general, persons who have been infected previously with M. tuberculosis may be less susceptible to subsequent infection. However, reinfection can occur among previously infected persons, especially if they are severely immunocompromised. Vaccination with Bacille of Calmette and Guérin (BCG) probably does not affect the risk for infection; rather, it decreases the risk for progressing from latent TB infection to active TB. Finally, although it is well established that HIV infection increases the likelihood of progressing from latent TB infection to active TB, it is unknown whether HIV infection increases the risk for becoming infected if exposed to M. tuberculosis.

Epidemiology

Several TB outbreaks among persons in health care facilities have been reported recently in the United States. Many of these outbreaks involved transmission of multidrug-resistant strains of M. tuberculosis to both patients and HCWs. Most of the patients and some of the HCWs were HIV-infected persons in whom new infection progressed rapidly to active disease. Mortality associated with those outbreaks was high (with a range of 43 to 93%). Furthermore, the interval between diagnosis and death was brief (with a range of median intervals of 4 to 16 weeks). Factors contributing to these outbreaks included delayed diagnosis of TB, delayed recognition of drug resistance and delayed initiation of effective therapy, all of which resulted in prolonged infectiousness, delayed initiation and inadequate duration of TB isolation, inadequate ventilation in TB isolation rooms, lapses in TB isolation practices and inadequate precautions for cough-inducing procedures and lack of adequate respiratory protection.

Fundamentals of TB infection control

An effective TB infection-control programme requires early identification, isolation and effective treatment of persons who have active TB. The primary emphasis of the TB infection-control plan should be on achieving these three goals. In all health care facilities, particularly those in which persons who are at high risk for TB work or receive care, policies and procedures for TB control should be developed, reviewed periodically and evaluated for effectiveness to determine the actions necessary to minimize the risk for transmission of M. tuberculosis.

The TB infection-control programme should be based on a hierarchy of control measures. The first level of the hierarchy, and that which affects the largest number of persons, is using administrative measures intended primarily to reduce the risk for exposing uninfected persons to persons who have infectious TB. These measures include:

• developing and implementing effective written policies and protocols to ensure the rapid identification, isolation, diagnostic evaluation and treatment of persons likely to have TB

• implementing effective work practices among HCWs in the health care facility (e.g., correctly wearing respiratory protection and keeping doors to isolation rooms closed)

• educating, training and counselling HCWs about TB

• screening HCWs for TB infection and disease.

The second level of the hierarchy is the use of engineering controls to prevent the spread and reduce the concentration of infectious droplet nuclei. These controls include:

• direct source control using local exhaust ventilation

• controlling direction of airflow to prevent contamination of air in areas adjacent to the infectious source

• diluting and removing contaminated air via general ventilation

• air cleaning via air filtration or ultraviolet germicidal irradiation (UVGI).

The first two levels of the hierarchy minimize the number of areas in the health care facility where exposure to infectious TB may occur, and they reduce, but do not eliminate, the risk in those few areas where exposure to M. tuberculosis can still occur (e.g., rooms in which patients with known or suspected infectious TB are being isolated and treatment rooms in which cough-inducing or aerosol-generating procedures are performed on such patients). Because persons entering such rooms may be exposed to M. tuberculosis, the third level of the hierarchy is the use of personal respiratory protective equipment in these and certain other situations in which the risk for infection with M. tuberculosis may be relatively higher.

Specific measures to reduce the risk for transmission of M. tuberculosis include the following:

1.    Assigning to specific persons in the health care facility the supervisory responsibility for designing, implementing, evaluating and maintaining the TB infection-control programme.

2.    Conducting a risk assessment to evaluate the risk for transmission of M. tuberculosis in all areas of the health care facility, developing a written TB infection-control programme based on the risk assessment and periodically repeating the risk assessment to evaluate the effectiveness of the TB infection-control programme. TB infection-control measures for each health care facility should be based on a careful assessment of the risk for transmission of M. tuberculosis in that particular setting. The first step in developing the TB infection-control programme should be to conduct a baseline risk assessment to evaluate the risk for transmission of M. tuberculosis in each area and occupational group in the facility. Appropriate infection-control interventions can then be developed on the basis of actual risk. Risk assessments should be performed for all inpatient and outpatient settings (e.g., medical and dental offices). Classification of risk for a facility, for a specific area and for a specific occupational group should be based on the profile of TB in the community, the number of infectious TB patients admitted to the area or ward, or the estimated number of infectious TB patients to whom HCWs in an occupational group may be exposed and the results of analysis of HCW PPD test conversions (where applicable) and possible person-to-person transmission of M. tuberculosis. Regardless of risk level, the management of patients with known or suspected infectious TB should not vary. However, the index of suspicion for infectious TB among patients, the frequency of HCW PPD skin testing, the number of TB isolation rooms and other factors will depend on the level of risk for transmission of M. tuberculosis in the facility, area or occupational group.

3.    Developing, implementing and enforcing policies and protocols to ensure early identification, diagnostic evaluation and effective treatment of patients who may have infectious TB. A diagnosis of TB may be considered for any patient who has a persistent cough (i.e., a cough lasting for longer than 3 weeks) or other signs or symptoms compatible with active TB (e.g., bloody sputum, night sweats, weight loss, anorexia or fever). However, the index of suspicion for TB will vary in different geographic areas and will depend on the prevalence of TB and other characteristics of the population served by the facility. The index of suspicion for TB should be very high in geographic areas or among groups of patients in which the prevalence of TB is high. Appropriate diagnostic measures should be conducted and TB precautions implemented for patients in whom active TB is suspected.

4.    Providing prompt triage for and appropriate management of patients in the outpatient setting who may have infectious TB. Triage of patients in ambulatory-care settings and emergency departments should include vigorous efforts to identify promptly patients who have active TB. HCWs who are the first points of contact in facilities that serve populations at risk for TB should be trained to ask questions that will facilitate identification of patients with signs and symptoms suggestive of TB. Patients with signs or symptoms suggestive of TB should be evaluated promptly to minimize the amount of time they are in ambulatory-care areas. TB precautions should be followed while the diagnostic evaluation is being conducted for these patients. TB precautions in the ambulatory-care setting should include placing these patients in a separate area apart from other patients and not in open waiting areas (ideally, in a room or enclosure meeting TB isolation requirements), giving these patients surgical masks to wear and instructing them to keep their masks on and giving these patients tissues and instructing them to cover their mouths and noses with the tissues when coughing or sneezing. Surgical masks are designed to prevent the respiratory secretions of the person wearing the mask from entering the air. When not in a TB isolation room, patients suspected of having TB should wear surgical masks to reduce the expulsion of droplet nuclei into the air. These patients do not need to wear particulate respirators, which are designed to filter the air before it is inhaled by the person wearing the mask. Patients suspected of having or known to have TB should never wear a respirator that has an exhalation valve, because the device would provide no barrier to the expulsion of droplet nuclei into the air.

5.    Promptly initiating and maintaining TB isolation for persons who may have infectious TB and who are admitted to the inpatient setting. In hospitals and other inpatient facilities, any patient suspected of having or known to have infectious TB should be placed in a TB isolation room that has currently recommended ventilation characteristics (see below). Written policies for initiating isolation should specify the indications for isolation, the person(s) authorized to initiate and discontinue isolation, the isolation practices to follow, the monitoring of isolation, the management of patients who do not adhere to isolation practices and the criteria for discontinuing isolation.

6.    Effectively planning arrangements for discharge. Before a TB patient is discharged from the health care facility, the facility’s staff and public health authorities should collaborate to ensure continuation of therapy. Discharge planning in the health care facility should include, at a minimum, a confirmed outpatient appointment with the provider who will manage the patient until the patient is cured, sufficient medication to take until the outpatient appointment and placement into case management (e.g., directly observed therapy (DOT)) or outreach programmes of the public health department. These plans should be initiated and in place before the patient’s discharge.

7.    Developing, installing, maintaining and evaluating ventilation and other engineering controls to reduce the potential for airborne exposure to M. tuberculosis. Local exhaust ventilation is a preferred source control technique, and it is often the most efficient way to contain airborne contaminants because it captures these contaminants near their source before they can disperse. Therefore, the technique should be used, if feasible, wherever aerosol-generating procedures are performed. Two basic types of local exhaust devices use hoods: the enclosing type, in which the hood either partially or fully encloses the infectious source, and the exterior type, in which the infectious source is near but outside the hood. Fully enclosed hoods, booths or tents are always preferable to exterior types because of their superior ability to prevent contaminants from escaping into the HCW’s breathing zone. General ventilation can be used for several purposes, including diluting and removing contaminated air, controlling airflow patterns within rooms and controlling the direction of airflow throughout a facility. General ventilation maintains air quality by two processes: dilution and removal of airborne contaminants. Uncontaminated supply air mixes with the contaminated room air (i.e., dilution), which is subsequently removed from the room by the exhaust system. These processes reduce the concentration of droplet nuclei in the room air. Recommended general ventilation rates for health care facilities are usually expressed in number of air changes per hour (ACH).

This number is the ratio of the volume of air entering the room per hour to the room volume and is equal to the exhaust airflow (Q, in cubic feet per minute) divided by the room volume (V, in cubic feet) multiplied by 60 (i.e., ACH = Q / V x 60). For the purposes of reducing the concentration of droplet nuclei, TB isolation and treatment rooms in existing health care facilities should have an airflow of greater than 6 ACH. Where feasible, this airflow rate should be increased to at least 12 ACH by adjusting or modifying the ventilation system or by using auxiliary means (e.g., recirculation of air through fixed HEPA filtration systems or portable air cleaners). New construction or renovation of existing health care facilities should be designed so that TB isolation rooms achieve an airflow of at least 12 ACH. The general ventilation system should be designed and balanced so that air flows from less contaminated (i.e., more clean) to more contaminated (less clean) areas. For example, air should flow from corridors into TB isolation rooms to prevent spread of contaminants to other areas. In some special treatment rooms in which operative and invasive procedures are performed, the direction of airflow is from the room to the hallway to provide cleaner air during these procedures. Cough-inducing or aerosol-generating procedures (e.g., bronchoscopy and irrigation of tuberculous abscesses) should not be performed in rooms with this type of airflow on patients who may have infectious TB. HEPA filters may be used in a number of ways to reduce or eliminate infectious droplet nuclei from room air or exhaust. These methods include placement of HEPA filters in exhaust ducts discharging air from booths or enclosures into the surrounding room, in ducts or in ceiling- or wall-mounted units, for recirculation of air within an individual room (fixed recirculation systems), in portable air cleaners, in exhaust ducts to remove droplet nuclei from air being discharged to the outside, either directly or through ventilation equipment, and in ducts discharging air from the TB isolation room into the general ventilation system. In any application, HEPA filters should be installed carefully and maintained meticulously to ensure adequate functioning. For general use areas in which the risk for transmission of M. tuberculosis is relatively high, ultraviolet lamps (UVGI) may be used as an adjunct to ventilation for reducing the concentration of infectious droplet nuclei, although the effectiveness of such units has not been evaluated adequately. Ultraviolet (UV) units can be installed in a room or corridor to irradiate the air in the upper portion of the room, or they can be installed in ducts to irradiate air passing through the ducts.

8.    Developing, implementing, maintaining and evaluating a respiratory protection programme. Personal respiratory protection (i.e., respirators) should be used by persons entering rooms in which patients with known or suspected infectious TB are being isolated, persons present during cough-inducing or aerosol-generating procedures performed on such patients and persons in other settings where administrative and engineering controls are not likely to protect them from inhaling infectious airborne droplet nuclei. These other settings include transporting patients who may have infectious TB in emergency transport vehicles and providing urgent surgical or dental care to patients who may have infectious TB before a determination has been made that the patient is non-infectious.

9.    Educating and training HCWs about TB, effective methods for preventing transmission of M. tuberculosis and the benefits of medical screening programmes. All HCWs, including physicians, should receive education regarding TB that is relevant to persons in their particular occupational group. Ideally, training should be conducted before initial assignment and the need for additional training should be re-evaluated periodically (e.g., once a year). The level and detail of this education will vary according to the HCW’s work responsibilities and the level of risk in the facility (or area of the facility) in which the HCW works. However, the programme may include the following elements:

• the basic concepts of M. tuberculosis transmission, pathogenesis and diagnosis,
  including information concerning the difference between latent TB infection and active
  TB disease, the signs and symptoms of TB and the possibility of reinfection

• the potential for occupational exposure to persons who have infectious TB in the
  health care facility, including information concerning the prevalence of TB in the
  community and facility, the ability of the facility to properly isolate patients who have
  active TB, and situations with increased risk for exposure to M. tuberculosis

• the principles and practices of infection control that reduce the risk for transmission of
  M. tuberculosis, including information concerning the hierarchy of TB infection-control
  measures and the written policies and procedures of the facility. Site-specific control
  measures should be provided to HCWs working in areas that require control
  measures in addition to those of the basic TB infection-control programme.

• the importance of proper maintenance for engineering controls (e.g., cleaning UVGI lamps and ensuring negative pressure in TB isolation rooms)

• the purpose of PPD skin testing, the significance of a positive PPD test result and the importance of participating in the skin-test programme

• the principles of preventive therapy for latent TB infection; these principles include the indications, use, effectiveness and the potential adverse effects of the drugs

• the HCW’s responsibility to seek prompt medical evaluation if a PPD test conversion
  occurs or if symptoms develop that could be caused by TB. Medical evaluation will
  enable HCWs who have TB to receive appropriate therapy and will help to prevent
  transmission of M. tuberculosis to patients and other HCWs.

• the principles of drug therapy for active TB

• the importance of notifying the facility if the HCW is diagnosed with active TB so that contact investigation procedures can be initiated

• the responsibilities of the facility to maintain the confidentiality of the HCW while
  ensuring that the HCW who has TB receives appropriate therapy and is non-
  infectious before returning to duty

• the higher risks associated with TB infection in persons who have HIV infection or
  other causes of severely impaired cell-mediated immunity, including (a) the more
  frequent and rapid development of clinical TB after infection with M. tuberculosis, (b)
  the differences in the clinical presentation of disease and (c) the high mortality rate associated with multiple drug resistant-TB in such persons

• the potential development of cutaneous anergy as immune function (as measured by CD4+ T-lymphocyte counts) declines

• information regarding the efficacy and safety of BCG vaccination and the principles of PPD screening among BCG recipients

• the facility’s policy on voluntary work reassignment options for immunocompromised HCWs.

10.    Developing and implementing a programme for routine periodic counselling and screening of HCWs for active TB and latent TB infection. A TB counselling, screening and prevention programme for HCWs should be established to protect both HCWs and patients. HCWs who have positive PPD test results, PPD test conversions or symptoms suggestive of TB should be identified, evaluated to rule out a diagnosis of active TB and started on therapy or preventive therapy if indicated. In addition, the results of the HCW PPD screening programme will contribute to evaluation of the effectiveness of current infection-control practices. Because of the increased risk for rapid progression from latent TB infection to active TB in human immunodeficiency virus, HIV-infected or otherwise severely immunocompromised persons, all HCWs should know if they have a medical condition or are receiving a medical treatment that may lead to severely impaired cell-mediated immunity. HCWs who may be at risk for HIV infection should know their HIV status (i.e., they should be encouraged to voluntarily seek counselling and testing for HIV antibody status). Existing guidelines for counselling and testing should be followed routinely. Knowledge of these conditions allows the HCW to seek the appropriate preventive measures and to consider voluntary work reassignments.

11.    ll HCWs should be informed about the need to follow existing recommendations for infection control to minimize the risk for exposure to infectious agents; implementation of these recommendations will greatly reduce the risk for occupational infections among HCWs. All HCWs should also be informed about the potential risks to severely immunocompromised persons associated with caring for patients who have some infectious diseases, including TB. It should be emphasized that limiting exposure to TB patients is the most protective measure that severely immunosuppressed HCWs can take to avoid becoming infected with M. tuberculosis. HCWs who have severely impaired cell-mediated immunity and who may be exposed to M. tuberculosis may consider a change in job-setting to avoid such exposure. HCWs should be advised of the legal option in many jurisdictions that severely immunocompromised HCWs can choose to transfer voluntarily to areas and work activities in which there is the lowest possible risk for exposure to M. tuberculosis. This choice should be a personal decision for HCWs after they have been informed of the risks to their health.

12.    Employers should make reasonable accommodations (e.g., alternative job assignments) for employees who have a health condition that compromises cell-mediated immunity and who work in settings where they may be exposed to M. tuberculosis. HCWs who are known to be immunocompromised should be referred to employee health professionals who can individually counsel the employees regarding their risk for TB. Upon the request of the immunocompromised HCW, employers should offer, but not compel, a work setting in which the HCW would have the lowest possible risk for occupational exposure to M. tuberculosis.

13.    All HCWs should be informed that immunosuppressed HCWs should have appropriate follow-up and screening for infectious diseases, including TB, provided by their medical practitioner. HCWs who are known to be HIV-infected or otherwise severely immunosuppressed should be tested for cutaneous anergy at the time of PPD testing. Consideration should be given to retesting, at least every 6 months, those immunocompromised HCWs who are potentially exposed to M. tuberculosis because of the high risk for rapid progression to active TB if they become infected.

14.    Information provided by HCWs regarding their immune status should be treated confidentially. If the HCW requests voluntary job reassignment, the privacy of the HCW should be maintained. Facilities should have written procedures on confidential handling of such information.

15.    Promptly evaluating possible episodes of M. tuberculosis transmission in health care facilities, including PPD skin-test conversions among HCWs, epidemiologically associated cases among HCWs or patients and contacts of patients or HCWs who have TB and who were not promptly identified and isolated. Epidemiological investigations may be indicated for several situations. These include, but are not limited to, the occurrence of PPD test conversions or active TB in HCWs, the occurrence of possible person-to-person transmission of M. tuberculosis and situations in which patients or HCWs with active TB are not promptly identified and isolated, thus exposing other persons in the facility to M. tuberculosis. The general objectives of the epidemiological investigations in these situations are as follows:

• to determine the likelihood that transmission of and infection with M. tuberculosis has occurred in the facility

• to determine the extent to which M. tuberculosis has been transmitted

• to identify those persons who have been exposed and infected, enabling them to receive appropriate clinical management

• to identify factors that could have contributed to transmission and infection and to implement appropriate interventions

• to evaluate the effectiveness of any interventions that are implemented and to ensure that exposure to and transmission of M. tuberculosis have been terminated.

16.    Coordinating activities with the local public health department, emphasizing reporting and ensuring adequate   discharge follow-up and the continuation and completion of therapy. As soon as a patient or HCW is known or suspected to have active TB, the patient or HCW should be reported to the public health department so that appropriate follow-up can be arranged and a community contact investigation can be performed. The health department should be notified well before patient discharge to facilitate follow-up and continuation of therapy. A discharge plan coordinated with the patient or HCW, the health department and the inpatient facility should be implemented.

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Prevention of occupational transmission of bloodborne pathogens (BBP) including the human immunodeficiency virus (HIV), hepatitis B virus (HBV) and more recently hepatitis C virus (HCV), has received significant attention. Although HCWs are the primary occupational group at risk of acquisition of infection, any worker who is exposed to blood or other potentially infectious body fluids during the performance of job duties is at risk. Populations at risk for occupational exposure to BBP include workers in health care delivery, public safety and emergency response workers and others such as laboratory researchers and morticians. The potential for occupational transmission of bloodborne pathogens including HIV will continue to increase as the number of persons who have HIV and other bloodborne infections and require medical care increases.

In the US, the Centers for Disease Control and Prevention (CDC) recommended in 1982 and 1983 that patients with the acquired immunodeficiency syndrome (AIDS) be treated according to the (now obsolete) category of “blood and body fluid precautions” (CDC 1982; CDC 1983). Documentation that HIV, the causative agent of AIDS, had been transmitted to HCWs by percutaneous and mucocutaneous exposures to HIV-infected blood, as well as the realization that the HIV infection status of most patients or blood specimens encountered by HCWs would be unknown at the time of the encounter, led CDC to recommend that blood and body fluid precautions be applied to all patients, a concept known as “universal precautions” (CDC 1987a, 1987b). The use of universal precautions eliminates the need to identify patients with bloodborne infections, but is not intended to replace general infection control practices. Universal precautions include the use of handwashing, protective barriers (e.g., goggles, gloves, gowns and face protection) when blood contact is anticipated and care in the use and disposal of needles and other sharp instruments in all health care settings. Also, instruments and other reusable equipment used in performing invasive procedures should be appropriately disinfected or sterilized (CDC 1988a, 1988b). Subsequent CDC recommendations have addressed prevention of transmission of HIV and HBV to public safety and emergency responders (CDC 1988b), management of occupational exposure to HIV, including the recommendations for the use of zidovudine (CDC 1990), immunization against HBV and management of HBV exposure (CDC 1991a), infection control in dentistry (CDC 1993) and the prevention of HIV transmission from HCWs to patients during invasive procedures (CDC 1991b).

In the US, CDC recommendations do not have the force of law, but have often served as the foundation for government regulations and voluntary actions by industry. The Occupational Health and Safety Administration (OSHA), a federal regulatory agency, promulgated a standard in 1991 on Occupational Exposure to Bloodborne Pathogens (OSHA 1991). OSHA concluded that a combination of engineering and work practice controls, personal protective clothing and equipment, training, medical surveillance, signs and labels and other provisions can help to minimize or eliminate exposure to bloodborne pathogens. The standard also mandated that employers make available hepatitis B vaccination to their employees.

The World Health Organization (WHO) has also published guidelines and recommendations pertaining to AIDS and the workplace (WHO 1990, 1991). In 1990, the European Economic Council (EEC) issued a council directive (90/679/EEC) on protection of workers from risks related to exposure to biological agents at work. The directive requires employers to conduct an assessment of the risks to the health and safety of the worker. A distinction is drawn between activities where there is a deliberate intention to work with or use biological agents (e.g., laboratories) and activities where exposure is incidental (e.g., patient care). Control of risk is based on a hierarchical system of procedures. Special containment measures, according to the classification of the agents, are set out for certain types of health facilities and laboratories (McCloy 1994). In the US, CDC and the National Institutes of Health also have specific recommendations for laboratories (CDC 1993b).

Since the identification of HIV as a BBP, knowledge about HBV transmission has been helpful as a model for understanding modes of transmission of HIV. Both viruses are transmitted via sexual, perinatal and bloodborne routes. HBV is present in the blood of individuals positive for hepatitis B e antigen (HBeAg, a marker for high infectivity) at a concentration of approximately 10⁸ to 10⁹ viral particles per millilitre (ml) of blood (CDC 1988b). HIV is present in blood at much lower concentrations: 10³ to 10⁴ viral particles/ml for a person with AIDS and 10 to 100/ml for a person with asymptomatic HIV infection (Ho, Moudgil and Alam 1989). The risk of HBV transmission to a HCW after percutaneous exposure to HBeAg-positive blood is approximately 100-fold higher than the risk of HIV transmission after percutaneous exposure to HIV-infected blood (i.e., 30% versus 0.3%) (CDC 1989).

Hepatitis

Hepatitis, or inflammation of the liver, can be caused by a variety of agents, including toxins, drugs, autoimmune disease and infectious agents. Viruses are the most common cause of hepatitis (Benenson 1990). Three types of bloodborne viral hepatitis have been recognized: hepatitis B, formerly called serum hepatitis, the major risk to HCWs; hepatitis C, the major cause of parenterally transmitted non-A, non-B hepatitis; and hepatitis D, or delta hepatitis.

Hepatitis B. The major infectious bloodborne occupational hazard to HCWs is HBV. Among US HCWs with frequent exposure to blood, the prevalence of serological evidence of HBV infection ranges between approximately 15 and 30%. In contrast, the prevalence in the general populations averages 5%. The cost-effectiveness of serological screening to detect susceptible individuals among HCWs depends on the prevalence of infection, the cost of testing and the vaccine costs. Vaccination of persons who already have antibodies to HBV has not been shown to cause adverse effects. Hepatitis B vaccine provides protection against hepatitis B for at least 12 years after vaccination; booster doses currently are not recommended. The CDC estimated that in 1991 there were approximately 5,100 occupationally acquired HBV infections in HCWs in the United States, causing 1,275 to 2,550 cases of clinical acute hepatitis, 250 hospitalizations and about 100 deaths (unpublished CDC data). In 1991, approximately 500 HCWs became HBV carriers. These individuals are at risk of long-term sequelae, including disabling chronic liver disease, cirrhosis and liver cancer.

The HBV vaccine is recommended for use in HCWs and public safety workers who may be exposed to blood in the workplace (CDC 1991b). Following a percutaneous exposure to blood, the decision to provide prophylaxis must include considerations of several factors: whether the source of the blood is available, the HBsAg status of the source and the hepatitis B vaccination and vaccine-response status of the exposed person. For any exposure of a person not previously vaccinated, hepatitis B vaccination is recommended. When indicated, hepatitis B immune globulin (HBIG) should be administered as soon as possible after exposure since its value beyond 7 days after exposure is unclear. Specific CDC recommendations are indicated in table 1 (CDC 1991b).

Table 1. Recommendation for post-exposure prophylaxis for percutaneous or permucosal exposure to hepatitis B virus, United States

¹ HBsAg = Hepatitis B surface antigen. ² HBIG = Hepatitis B immune globulin; dose 0.06 mL/kg IM. ³ HB vaccine = hepatitis B vaccine.  ⁴ Anti-HBs = antibody to hepatitis B surface antigen. ⁵ Adequate anti-HBs is ≥10 mIU/mL.

Table 2. Provisional US Public Health Service recommendations for chemoprophylaxis after occupational exposure to HIV, by type of exposure and source of material, 1996

¹ Any exposure to concentrated HIV (e.g., in a research laboratory or production facility) is treated as percutaneous exposure to blood with highest risk.  ² Recommend—Postexposure prophylaxis (PEP) should be recommended to the exposed worker with counselling. Offer—PEP should be offered to the exposed worker with counselling. Not offer—PEP should not be offered because these are not occupational exposures to HIV.  ³ Regimens: zidovudine (ZDV), 200 mg three times a day; lamivudine (3TC), 150 mg two times a day; indinavir (IDV), 800 mg three times a day (if IDV is not available, saquinavir may be used, 600 mg three times a day). Prophylaxis is given for 4 weeks. For full prescribing information, see package inserts. ⁴ Risk definitions for percutaneous blood exposure: Highest risk—BOTH larger volume of blood (e.g., deep injury with large diameter hollow needle previously in source patient’s vein or artery, especially involving an injection of source-patient’s blood) AND blood containing a high titre of HIV (e.g., source with acute retroviral illness or end-stage AIDS; viral load measurement may be considered, but its use in relation to PEP has not been evaluated). Increased risk—EITHER exposure to larger volume of blood OR blood with a high titre of HIV. No increased risk—NEITHER exposure to larger volume of blood NOR blood with a high titre of HIV (e.g., solid suture needle injury from source patient with asymptomatic HIV infection).  ⁵ Possible toxicity of additional drug may not be warranted. ⁶ Includes semen; vaginal secretions; cerebrospinal, synovial, pleural, peritoneal, pericardial and amniotic fluids.  ⁷ For skin, risk is increased for exposures involving a high titre of HIV, prolonged contact, an extensive area, or an area in which skin integrity is visibly compromised. For skin exposures without increased risk, the risk for drug toxicity outweighs the benefit of PEP.

Article 14(3) of EEC Directive 89/391/EEC on vaccination required only that effective vaccines, where they exist, be made available for exposed workers who are not already immune. There was an amending Directive 93/88/EEC which contained a recommended code of practice requiring that workers at risk be offered vaccination free of charge, informed of the benefits and disadvantages of vaccination and non-vaccination, and be provided a certificate of vaccination (WHO 1990).

The use of hepatitis B vaccine and appropriate environmental controls will prevent almost all occupational HBV infections. Reducing blood exposure and minimizing puncture injuries in the health care setting will reduce also the risk of transmission of other bloodborne viruses.

Hepatitis C. Transmission of HCV is similar to that of HBV, but infection persists in most patients indefinitely and more frequently progresses to long-term sequelae (Alter et al. 1992). The prevalence of anti-HCV among US hospital-based health care workers averages 1 to 2% (Alter 1993). HCWs who sustain accidental injuries from needlesticks contaminated with anti-HCV-positive blood have a 5 to 10% risk of acquiring HCV infection (Lampher et al. 1994; Mitsui et al. 1992). There has been one report of HCV transmission after a blood splash to the conjunctiva (Sartori et al. 1993). Prevention measures again consist of adherence to universal precautions and percutaneous injury prevention, since no vaccine is available and immune globulin does not appear to be effective.

Hepatitis D. Hepatitis D virus requires the presence of hepatitis B virus for replication; thus, HDV can infect persons only as a coinfection with acute HBV or as a superinfection of chronic HBV infection. HDV infection can increase the severity of liver disease; one case of occupationally acquired HDV infection hepatitis has been reported (Lettau et al. 1986). Hepatitis B vaccination of HBV-susceptible persons will also prevent HDV infection; however, there is no vaccine to prevent HDV superinfection of an HBV carrier. Other prevention measures consist of adherence to universal precautions and percutaneous injury prevention.

HIV

The first cases of AIDS were recognized in June of 1981. Initially, over 92% of the cases reported in the United States were in homosexual or bisexual men. However, by the end of 1982, AIDS cases were identified among injection drug users, blood transfusion recipients, haemophilia patients treated with clotting factor concentrates, children and Haitians. AIDS is the result of infection with HIV, which was isolated in 1985. HIV has spread rapidly. In the United States, for example, the first 100,000 AIDS cases occurred between 1981 and 1989; the second 100,000 cases occurred between 1989 and 1991. As of June 1994, 401,749 cases of AIDS had been reported in the United States (CDC 1994b).

Globally, HIV has affected many countries including those in Africa, Asia and Europe. As of 31 December 1994, 1,025,073 cumulative cases of AIDS in adults and children had been reported to the WHO. This represented a 20% increase from the 851,628 cases reported through December 1993. It was estimated that 18 million adults and about 1.5 million children have been infected with HIV since the beginning of the pandemic (late 1970s to early 1980s) (WHO 1995).

Although HIV has been isolated from human blood, breast milk, vaginal secretions, semen, saliva, tears, urine, cerebrospinal fluid and amniotic fluid, epidemiological evidence has implicated only blood, semen, vaginal secretions and breast milk in the transmission of the virus. The CDC has also reported on the transmission of HIV as the result of contact with blood or other body secretions or excretions from an HIV-infected person in the household (CDC 1994c). Documented modes of occupational HIV transmission include having percutaneous or mucocutaneous contact with HIV-infected blood. Exposure by the percutaneous route is more likely to result in infection transmission than is mucocutaneous contact.

There are a number of factors which may influence the likelihood of occupational bloodborne pathogen transmission, including: the volume of fluid in the exposure, the virus titre, the length of time of the exposure and the immune status of the worker. Additional data are needed to determine precisely the importance of these factors. Preliminary data from a CDC case-control study indicate that for percutaneous exposures to HIV-infected blood, HIV transmission is more likely if the source patient has advanced HIV disease and if the exposure involves a larger inoculum of blood (e.g., injury due to a large-bore hollow needle) (Cardo et al. 1995). Virus titre can vary between individuals and over time within a single individual. Also, blood from persons with AIDS, particularly in the terminal stages, may be more infectious than blood from persons in earlier stages of HIV infection, except possibly during the illness associated with acute infection (Cardo et al. 1995).

Occupational exposure and HIV infection

As of December 1996, CDC reported 52 HCWs in the United States who have seroconverted to HIV following a documented occupational exposure to HIV, including 19 laboratory workers, 21 nurses, six physicians and six in other occupations. Forty-five of the 52 HCWs sustained percutaneous exposures, five had mucocutaneous exposures, one had both a percutaneous and a mucocutaneous exposure and one had an unknown route of exposure. In addition, 111 possible cases of occupationally acquired infection have been reported. These possible cases have been investigated and are without identifiable non-occupational or transfusion risks; each reported percutaneous or mucocutaneous occupational exposures to blood or body fluids, or laboratory solutions containing HIV, but HIV seroconversion specifically resulting from an occupational exposure was not documented (CDC 1996a).

In 1993, the AIDS Centre at the Communicable Disease Surveillance Centre (UK) summarized reports of cases of occupational HIV transmission including 37 in the United States, four in the UK and 23 from other countries (France, Italy, Spain, Australia, South Africa, Germany and Belgium) for a total of 64 documented seroconversions after a specific occupational exposure. In the possible or presumed category there were 78 in the United States, six in the UK and 35 from other countries (France, Italy, Spain, Australia, South Africa, Germany, Mexico, Denmark, Netherlands, Canada and Belgium) for a total of 118 (Heptonstall, Porter and Gill 1993). The number of reported occupationally acquired HIV infections is likely to represent only a portion of the actual number due to under-reporting and other factors.

HIV post-exposure management

Employers should make available to workers a system for promptly initiating evaluation, counselling and follow-up after a reported occupational exposure that may place a worker at risk of acquiring HIV infection. Workers should be educated and encouraged to report exposures immediately after they occur so that appropriate interventions can be implemented (CDC 1990).

If an exposure occurs, the circumstances should be recorded in the worker’s confidential medical record. Relevant information includes the following: date and time of exposure; job duty or task being performed at the time of exposure; details of exposure; description of source of exposure, including, if known, whether the source material contained HIV or HBV; and details about counselling, post-exposure management and follow-up. The source individual should be informed of the incident and, if consent is obtained, tested for serological evidence of HIV infection. If consent cannot be obtained, policies should be developed for testing source individuals in compliance with applicable regulations. Confidentiality of the source individual should be maintained at all times.

If the source individual has AIDS, is known to be HIV seropositive, refuses testing or the HIV status is unknown, the worker should be evaluated clinically and serologically for evidence of HIV infection as soon as possible after the exposure (baseline) and, if seronegative, should be retested periodically for a minimum of 6 months after exposure (e.g., six weeks, 12 weeks and six months after exposure) to determine whether HIV infection has occurred. The worker should be advised to report and seek medical evaluation for any acute illness that occurs during the follow-up period. During the follow-up period, especially the first six to 12 weeks after the exposure, exposed workers should be advised to refrain from blood, semen or organ donation and to abstain from, or use measures to prevent HIV transmission, during sexual intercourse.

In 1990, CDC published a statement on the management of exposure to HIV including considerations regarding zidovudine (ZDV) post-exposure use. After a careful review of the available data, CDC stated that the efficacy of zidovudine could not be assessed due to insufficient data, including available animal and human data (CDC 1990).

In 1996, information suggesting that ZDV post-exposure prophylaxis (PEP) may reduce the risk for HIV transmission after occupational exposure to HIV-infected blood (CDC 1996a) prompted a US Public Health Service (PHS) to update a previous PHS statement on management of occupational exposure to HIV with the following findings and recommendations on PEP (CDC 1996b). Although failures of ZDV PEP have occurred (Tokars et al. 1993), ZDV PEP was associated with a decrease of approximately 79% in the risk for HIV seroconversion after percutaneous exposure to HIV-infected blood in a case-control study among HCWs (CDC 1995).

Although information about the potency and toxicity of antiretroviral drugs is available from studies of HIV-infected patients, it is uncertain to what extent this information can be applied to uninfected persons receiving PEP. In HIV-infected patients, combination therapy with the nucleosides ZDV and lamivudine (3TC) has greater antiretroviral activity than ZDV alone and is active against many ZDV-resistant HIV strains without significantly increased toxicity (Anon. 1996). Adding a protease inhibitor provides even greater increases in antiretroviral activity; among protease inhibitors, indinavir (IDV) is more potent than saquinavir at currently recommended doses and appears to have fewer drug interactions and short-term adverse effects than ritonavir (Niu, Stein and Schnittmann 1993). Few data exist to assess possible long-term (i.e., delayed) toxicity resulting from use of these drugs in persons not infected with HIV.

The following PHS recommendations are provisional because they are based on limited data regarding efficacy and toxicity of PEP and risk for HIV infection after different types of exposure. Because most occupational exposures to HIV do not result in infection transmission, potential toxicity must be carefully considered when prescribing PEP. Changes in drug regimens may be appropriate, based on factors such as the probable antiretroviral drug resistance profile of HIV from the source patient, local availability of drugs and medical conditions, concurrent drug therapy and drug toxicity in the exposed worker. If PEP is used, drug-toxicity monitoring should include a complete blood count and renal and hepatic chemical function tests at baseline and two weeks after starting PEP. If subjective or objective toxicity is noted, drug reduction or drug substitution should be considered, and further diagnostic studies may be indicated.

Chemoprophylaxis should be recommended to exposed workers after occupational exposures associated with the highest risk for HIV transmission. For exposures with a lower, but non-negligible risk, PEP should be offered, balancing the lower risk against the use of drugs having uncertain efficacy and toxicity. For exposures with negligible risk, PEP is not justified (see table 2 ). Exposed workers should be informed that knowledge about the efficacy and toxicity of PEP is limited, that for agents other than ZDV, data are limited regarding toxicity in persons without HIV infection or who are pregnant and that any or all drugs for PEP may be declined by the exposed worker.

PEP should be initiated promptly, preferably with 1 to 2 hours post-exposure. Although animal studies suggest that PEP probably is not effective when started later than 24 to 36 hours post-exposure (Niu, Stein and Schnittmann 1993; Gerberding 1995), the interval after which there is no benefit from PEP for humans is undefined. Initiating therapy after a longer interval (e.g., 1 to 2 weeks) may be considered for the highest risk exposures; even if infection is not prevented, early treatment of acute HIV infection may be beneficial (Kinloch-de-los et al. 1995).

If the source patient or the patient’s HIV status is unknown, initiating PEP should be decided on a case-by-case basis, based on the exposure risk and likelihood of infection in known or possible source patients.

Other Bloodborne Pathogens

Syphilis, malaria, babesiosis, brucellosis, leptospirosis, arboviral infections, relapsing fever, Creutzfeldt-Jakob disease, human T-lymphotropic virus type 1 and viral haemorrhagic fever have also been transmitted by the bloodborne route (CDC 1988a; Benenson 1990). Occupational transmission of these agents has only rarely been recorded, if ever.

Prevention of Transmission of Bloodborne Pathogens

There are several basic strategies which relate to the prevention of occupational transmission of bloodborne pathogens. Exposure prevention, the mainstay of occupational health, can be accomplished by substitution (e.g., replacing an unsafe device with a safer one), engineering controls (i.e., controls that isolate or remove the hazard), administrative controls (e.g., prohibiting recapping of needles by a two-handed technique) and use of personal protective equipment. The first choice is to “engineer out the problem”.

In order to reduce exposures to bloodborne pathogens, adherence to general infection control principles, as well as strict compliance with universal precaution guidelines, is required. Important components of universal precautions include the use of appropriate personal protective equipment, such as gloves, gowns and eye protection, when exposure to potentially infectious body fluids is anticipated. Gloves are one of the most important barriers between the worker and the infectious material. While they do not prevent needlesticks, protection for the skin is provided. Gloves should be worn when contact with blood or body fluids is anticipated. Washing of gloves in not recommended. Recommendations also advise workers to take precautions to prevent injuries by needles, scalpels and other sharp instruments or devices during procedures; when cleaning used instruments; during disposal of used needles; and when handling sharp instruments after procedures.

Percutaneous exposures to blood

Since the major risk of infection results from parenteral exposure from sharp instruments such as syringe needles, engineering controls such as resheathing needles, needleless IV systems, blunt suture needles and appropriate selection and use of sharps disposal containers to minimize exposures to percutaneous injuries are critical components of universal precautions.

The most common type of percutaneous inoculation occurs through inadvertent needlestick injury, many of which are associated with recapping of needles. The following reasons have been indicated by workers as reasons for recapping: inability to properly dispose of needles immediately, sharps disposal containers too far away, lack of time, dexterity problems and patient interaction.

Needles and other sharp devices can be redesigned to prevent a significant proportion of percutaneous exposures. A fixed barrier should be provided between hands and the needle after use. Worker’s hands should remain behind the needle. Any safety feature should be an integral part of the device. The design should be simple and little or no training should be required (Jagger et al. 1988).

Implementing safer needle devices must be accompanied by evaluation. In 1992, the American Hospital Association (AHA) published a briefing to assist hospitals with the selection, evaluation and adoption of safer needle devices (AHA 1992). The briefing stated that “because safer needle devices, unlike drugs and other therapies, do not undergo clinical testing for safety and efficacy before they are marketed, hospitals are essentially ‘on their own’ when it comes to selecting appropriate products for their specific institutional needs”. Included in the AHA document are guidance for the evaluation and adoption of safer needle devices, case studies of the use of safety devices, evaluation forms and listing of some, but not all, products on the US market.

Prior to implementation of a new device, health care institutions must ensure that there is an appropriate needlestick surveillance system in place. In order to accurately assess the efficacy of new devices, the number of reported exposures should be expressed as an incidence rate.

Possible denominators for reporting the number of needlestick injuries include patient days, hours worked, number of devices purchased, number of devices used and number of procedures performed. The collection of specific information on device-related injuries is an important component of the evaluation of the effectiveness of a new device. Factors to be considered in collecting information on needlestick injuries include: new product distribution, stocking and tracking; identification of users; removal of other devices; compatibility with other devices (especially IV equipment); ease of use; and mechanical failure. Factors which may contribute to bias include compliance, subject selection, procedures, recall, contamination, reporting and follow-up. Possible outcome measures include rates of needlestick injuries, HCW compliance, patient care complications and cost.

Finally, training and feedback from workers are important components of any successful needlestick prevention programme. User acceptance is a critical factor, but one that seldom receives enough attention.

Elimination or reduction of percutaneous injuries should result if adequate engineering controls are available. If HCWs, product evaluation committees, administrators and purchasing departments all work together to identify where and what safer devices are needed, safety and cost effectiveness can be combined. Occupational transmission of bloodborne pathogens is costly, both in terms of money and the impact on the employee. Every needlestick injury causes undue stress on the employee and may affect job performance. Referral to mental health professionals for supportive counselling may be required.

In summary, a comprehensive approach to prevention is essential to maintaining a safe and healthy environment in which to provide health care services. Prevention strategies include the use of vaccines, post-exposure prophylaxis and prevention or reduction of needlestick injuries. Prevention of needlestick injuries can be accomplished by improvement in the safety of needle-bearing devices, development of procedures for safer use and disposal and adherence to infection control recommendations.

Acknowledgements: The authors thank Mariam Alter, Lawrence Reed and Barbara Gooch for their manuscript review.

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