Michael L. Wilson
Clinical laboratories are an area of special concern in hospital infection control. Laboratory workers may be exposed to infectious agents during all steps of collection, transport, processing, and analysis of patients' specimens. The clinical microbiology staff in particular are at risk of occupational infection because the clinical specimens submitted for cultures are likely to contain infectious agents and the process of isolation and culture generates large numbers of pathogenic microor-ganisms.
The goals of this chapter are to provide an overview of the epidemiology of laboratory-acquired infections, to highlight those infections of special concern to laboratories, and to make specific recommendations for the prevention and control of laboratory-acquired infections. Not discussed in this chapter are the individual problems of clinical virology, research, anatomic pathology, commercial reference laboratories, or laboratories involved in the production or processing of large volumes of pathogenic microorganisms. The reader is referred to Collins' monograph for an extensive review of the subject of laboratory-acquired infections [1]. The roles of the clinical microbiology laboratory in infection surveillance, investigation of endemic and epidemic hospital infections, and the control of healthcare-associated infections are discussed in Chapters 6, 7, and 10, respectively.
Incidence, Causative Agents, and Cost
The true incidence of laboratory-acquired infections remains unknown. Early data were derived from surveys, personal communications, and literature reports, information that cannot be used to calculate incidence rates [2,3,4,5]. More recent data are derived from surveys, which again cannot be used to calculate true incidence rates. One survey [6] did report an annual incidence of three laboratory-acquired infections per 1,000 employees, and another [7] reported annual incidences of 1.4 and 3.5 per 1,000 employees among workers in hospital-based and public health laboratories, respectively. A recent survey from U.K. laboratories during 1994–1995 reported an incidence rate of 16.2 infections per 100,000 person-years, compared with a rate of 82.7 infections per 100,000 person-years during 1988–1989 [8]. Despite the limitations of the published data, it seems reasonable that the annual incidence of laboratory-acquired infections is between 1–5 infections per 1,000 employees. There is some evidence that the annual incidence is declining [2], particularly for hepatitis B virus (HBV) infections [9], owing to HBV immunization and adoption of standard precautions [10].
In years past, the most common laboratory-acquired infections were brucellosis, Q fever, typhoid fever, HBV,
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or tuberculosis [3,4]. More recent data show that the infections now most commonly acquired in clinical laboratories are HBV, shigellosis, or tuberculosis [6,11]. Other agents continue to pose a hazard to laboratory workers, however, as demonstrated by continuing reports of laboratory-acquired brucellosis [12,13,14,15,16,17], Escherichia coli 0157:H7 [18,19], salmonellosis [20,21,22,23], and meningococcemia [24,25,26].
The cost to healthcare systems for these infections is unknown. In one report [7], each laboratory-acquired infection resulted in an average of 1.2 lost work days for hospital-based laboratories and 1.3 lost work days for public health laboratories. The latter figure, however, does not include the 48 work days lost when one employee was hospitalized for a laboratory-acquired infection.
An accurate estimate of the cost to healthcare systems may not be possible without additional data or further studies, but it is clear that the cost to an infected individual can be high. It has been estimated that 200 to 300 healthcare workers (HCWs) die each year as a consequence of chronic HBV infection [27]. Because the risk to laboratorians of acquiring HBV equals or exceeds that of other HCWs [28,29], it seems reasonable that a substantial proportion of these deaths occur among laboratorians. There also are fatal laboratory-acquired infections caused by other pathogens [21,25]. Laboratory-acquired infection with human immunodeficiency virus (HIV), resulting in acquired immunodeficiency syndrome, has been reported in laboratory workers [30,31,32] who account for ~25% of reported occupational transmissions.
Sources of Infections
Pike [2,3] and others [6,7,33,34] have attempted to determine which laboratory procedures, accidents, or other exposures to infectious agents are the source of laboratory-acquired infections (Table 22-1). These data indicate that the source of infection is unknown in ≤20% of episodes and that the infected individual is known only to have worked with the agents in the past in another 21% of episodes [3]. Thus, the exact source, procedure, or breach in technique can be identified in just over 50% of episodes. Among the recognized sources are accidents, which account for 18% of episodes. The types of accidents that lead to laboratory-acquired infections are listed in Table 22-2.
Laboratory accidents associated with exposure to infectious materials include creation of aerosols from spatters or spills; exposure of skin defects (cuts, abrasions, ulcers, dermatitis, etc.), conjunctivas, or mucosal surfaces; accidental aspiration or ingestions; and traumatic implantation [3]. Needle-stick injuries (NSI) and cuts with broken glass and other sharp objects account for up to 50% of accidents associated with laboratory-acquired infections [35,36]. The microbiological hazards associated with injuries from needle sticks and sharp objects have recently been reviewed [35,36], despite the fact that such behavior is proscribed in all laboratories [37,38,39].
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TABLE 22-1 |
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Aerosol droplets vary in size, with larger droplets rapidly settling onto exposed surfaces. These droplets may carry infectious agents and can thus contaminate environmental surfaces. Smaller droplets remain suspended in the air for a longer period of time and, under the appropriate environmental conditions, can remain suspended indefinitely. Aerosols with droplets measuring <5 mm in diameter can be inhaled directly into alveoli; those measuring ~1 mm are the most likely to be retained within alveoli [40]. Many common laboratory procedures have been shown to produce aerosols in the size range [41,42,43,44]. Both Mycobacterium tuberculosis and nontuberculous mycobacteria may be transmitted by the aerosol route [45].
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TABLE 22-2 |
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Laboratory personnel have among the highest rates of NSI in HCWs [36,46]. Most NSI occur during disposal of used needles, assembly or disassembly of intravenous infusion sets, administration of parenteral injections or infusion therapy, drawing of blood, recapping of needles, or handling of waste that contains needles [36,46,47,48]. Recapping needles is particularly hazardous, causing 12%–30% of NSI [36,46]. It should be noted, however, that not recapping needles also may be hazardous [49]. The epidemiology of NSI among laboratory personnel has not been studied, but because activities such as intravenous infusion and handling infusion sets are not carried out in laboratories, recapping needles and handling waster are likely to be the most common causes of NSI among laboratory personnel. One-handed recapping before disposal of needles may reduce this risk.
Infectious Agents of Special Concern in Clincal Laboratories
The risk of acquiring infections in a clinical laboratory depends on several factors, the most important of which is the likelihood of exposure to an infectious agent [50]. The probability that such an exposure will result in infection depends on inoculum size, viability of the infectious agent, immune status of the exposed individual, and availability of effective postexposure prophylactic (PEP) therapy.
Human Immunodeficiency Virus (HIV)
Although the prevalence of HIV in laboratory specimens depends on the patient population served by that laboratory, a significant minority of clinical specimens will contain HIV in most healthcare settings. As a result, all clinical laboratory personnel can expect to eventually work with HIV-infected clinical specimens. Transmission of HIV during an occupational exposure occurs as a result of contact with contaminated material with nonintact skin or mucosal surfaces or as a result of traumatic implantation of infectious material. It is estimated that the risk of acquiring HIV infection from a NSI is ~0.3% to 0.5% [50,51,52]. The frequency of exposures among laboratory personnel has not been reported, but based on the epidemiology of HBV infection among laboratory personnel [29,51], it is likely that these personnel are among those HCWs most commonly exposed to HIV-contaminated specimens. The prevalence of HBV serological markers among clinical laboratory workers who handle blood or serum matches or exceeds that of other HCWs, including nurses and surgeons [53].
Although effective PEP protocols exist, prevention of HIV infection among HCWs depends primarily on prevention of exposure to the virus. Guidelines for preventing HIV exposure in the workplace have been published; they are based on the principle of standard precautions (see Chapter 42). These guidelines also are useful in preventing occupational exposure to other BBPs, particularly HBV. The guidelines are based on a common-sense approach to infection control, and there is evidence that occupational exposures to HIV in patient specimens have been reduced when standard precautions are used [10,54]. Even though the cost of implementing standard precautions is substantial (and may have been significantly underestimated heretofore [55,56]), standard precautions provide the most rational approach to minimizing the risk of acquiring BBPs [54].
Hepatitis B Virus
Despite the availability of safe and effective vaccines and of effective postexposure treatment regimens, HBV infection (see Chapters 4 and 42) remains a common HAI [7,14,28]. Surveys repeatedly have shown that laboratorians are among the most frequently infected HCWs [6,19,28,53], with seropositivity rates between 2–27 times that of the general population [53,56,57,58,59,60]. It is estimated that of the 300,000 new episodes of HBV infection in the United States each year, 1% to 6% (6,000 to 18,000) occur in HCWs [9,61]. One report estimates that 12% of HBV-infected persons require hospitalization for HBV infections [9].
Because the incidence of HBV infection in a given population of patients may be high and is often underestimated and because compliance with barrier precautions often is inconsistent, the easiest way to prevent occupational HBV infection is by vaccination (see Chapters 4 and 42). The reported decrease in the incidence of laboratory-acquired HBV infection has been attributed to the introduction of HBV vaccine in 1982, since the decrease has occurred despite continued exposures [6,9,29,62,63]. Since 1992, the Occupational Safety and Health Administration has required that all employers have an exposure plan [65]. As part of this plan, employees are categorized as to the likelihood of occupational exposure to blood; those with such exposure are to be provided with HBV vaccination at no cost to the employee [64].
Employers should focus vaccination strategies on those employees most likely to be exposed because vaccinating employees with little or no risk of occupational exposure diverts resources from those employees who are at the highest risk [63]. Similarly, there is no compelling evidence to routinely perform postvaccination testing or provide booster doses; employers should not divert resources for either purpose [63]. Until all HCWs are willing to complete HBV vaccination, HBV is likely to remain a serious infection control issue in healthcare settings. Requiring HBV vaccination as a condition of employment may be the simplest way to ensure compliance.
Most laboratory-acquired HBV infections probably are not acquired via NSI or cuts with infected instruments but via clinically inapparent cutaneous or mucosal exposure to blood or blood products [28,58,60,65,66]. Therefore, rigid adherence to standard precautions should be followed
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by all laboratory personnel. Percutaneous exposure is not limited to those employees working directly with body fluids. One outbreak of laboratory-acquired HBV infections occurred among clerical employees whose only risk factor was exposure to HBV-contaminated computer requisitions [67]; in another study, the highest prevalence of seropositivity in a laboratory was among persons employed as glassware washers [68].
Hepatitis C Virus
Hepatitis C virus (HCV) (see Chapter 32) is transmitted via the same routes as HBV. Unlike HBV, HCV is not readily transmitted via NSI; estimates of the risk of transmission following NSI are in the range of 0%–10% [51,69,70,71]. Nonetheless, exposure is to be avoided because ≥50% of HCV-infected persons progress to chronic liver disease and cirrhosis or hepatocellular carcinoma or both will develop in many of them. As with HBV and HIV, HCV infection is highly prevalent in some populations of patients, such as injection drug users [72].
Mycobacterium Tuberculosis
Employees involved in the processing of clinical specimens or cultures from patients with tuberculosis (TB) (see Chapter 33) are at a much greater risk of acquiring TB than is the general population [11,73]. Once thought to be controlled in the United States, TB has reemerged as an important public health problem. Two issues are of particular importance to laboratory employees: the increasing incidence of TB and the development of strains that are resistant to several or all first-line chemotherapeutic agents. All healthcare facilities should have a comprehensive plan for the prevention, control, and treatment of TB [74].
Bacteria and Fungi
Bacterial infections of special concern to laboratory personnel are primarily those caused by highly virulent pathogens, such as Brucella, N. meningitidis, or Francisella tularensis[5,3,12,13,14,15,16,24,25,26] and the enteric pathogens Shigella, Salmonella, or E. coli O157:H7 [5,17,18,19,20,21,22,23,75]. Fungal pathogens of significance to laboratory employees include Coccidioides immitis, Blastomyces, dermatitidis, or Histoplasma capsulatum [76]. Recommendations for the safe processing of clinical specimens and cultures suspected of containing these agents are given later herein.
Prevention of Laboratory–Acquired Infections
Each clinical laboratory must develop policies and procedures to prevent, document, and treat laboratory-acquired infections. The laboratory director, in conjunction with a designated laboratory safety officer, should take the lead role in developing and implementing these policies and should integrate them into the laboratory procedure manual [1,37,38,39,75,77]. All employees should receive the appropriate education and training necessary to perform their jobs safely. They should be aware of hazards associated with various infectious agents and exactly what should be done should an exposure take place. Immunization against HBV should be required for all laboratory workers. Initial and follow-up tuberculin skin testing or serologic testing for M. tuberculosis antibodies should be given according to current guidelines. Finally, a method for maintaining compliance with these policies and procedures must be implemented along with the appropriate documentation, counseling, and, if necessary, disciplinary action to ensure that employees work safely.
Biosafety Levels
The Centers for Disease Control and Prevention (CDC) and National Institute of Health have published a document defining four biosafety levels based on “the potential hazard of the agent and the laboratory function or activity” [37]. Laboratory design, equipment, and procedures necessary to achieve each biosafety level are detailed in that document. Most common pathogens may be handled under biosafety level 2 conditions. Cultures suspected of containing Brucella, F. tularensis, M. tuberculosis, C. immitis, B. dermatitidis, or H. capsulatum should be processed only under biosafety level 3 conditions. Biosafety level 4 conditions are not needed in general clinical microbiology laboratories.
Standard Precautions
Special policies and procedures are necessary for the safe handling and disposal of certain highly virulent pathogens. Rigorous adherence to standard precautions is sufficient to lessen or eliminate the risk of acquiring an infection from most patients' specimens processed in clinical laboratories. Implementation of standard precautions will be successful only if laboratory administrators and workers integrate standard precautions into routine laboratory operations and make every reasonable attempt to maintain and enforce such policies. Standard precautions have been shown to decrease the number of occupational exposures to blood and other body fluids among one group of HCWs [10,53]. The CDC recommendations for standard precautions for all HCWs and clinical laboratories are given in Tables 22-3 and 22-4, respectively.
Standard Microbiological Practices
When used in conjunction with standard precautions, the following practices should be effective in preventing
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most laboratory-acquired infections. These or equivalent procedures should be routine practice in all clinical laboratories [38,39,78,79,80,81,82,83,84].
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TABLE 22-3 |
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TABLE 22-4 |
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Laboratory Access
Only trained personnel should be allowed in a laboratory under ordinary circumstances. Maintenance personnel, delivery persons, and other visitors with legitimate reason for being in the laboratory should either be escorted or be closely supervised to prevent unnecessary exposure to infectious agents. Laboratory trainees, house staff, and students also should be supervised closely. Children should not be allowed in laboratories.
Personnel Policies
All HCWs should have training commensurate with the level of expertise needed to safely perform all necessary procedures. Suggested topics for such training are given in Table 22-5[39]. All HCWs should receive the necessary continuing education and training to ensure job safety. Employee job appraisals should document lapses in safety, techniques, or other behaviors that could result in occupational exposure to infectious agents. Persons exhibiting such behavior should be counseled and/or retrained.
Laboratory Facility
Laboratories should be designed to minimize traffic and unnecessary access to work areas. Laboratory furniture should be sturdy and easy to clean, and laboratories themselves should be uncluttered and easy to clean. Foot-, knee-, or elbow-operated hand-washing sinks or waterless agents for hand hygiene should be available and located near laboratory exits. The laboratory facility should be designed and constructed to meet criteria recommended for the appropriate biosafety level [37].
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TABLE 22-5 |
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Hygiene for Workers
Eating, drinking, smoking, and applying cosmetics should be strictly prohibited within the laboratory [37]. All HCWs should wear and button full-length white laboratory coats while in the laboratory. HCWs and visitors should perform hand hygiene before leaving the laboratory. Food and other personal items should not be stored in refrigerators or freezers used to store clinical specimens or cultures. Refrigerators, freezers, and microwave ovens used to store or prepare food must be located outside the laboratory.
Clinical Specimens
Specimens must be labeled with the patient's full name, hospital identification number, and date drawn. Specimens received in damaged, leaking, or contaminated containers should not be processed; the person who collected the specimen should be notified and the specimens recollected.
Microbiological Techniques
Mouth pipetting should be strictly prohibited; mechanical pipetting devices should be used for all pipetting. All procedures should be performed in a way to minimize or prevent aerosols. Procedures that generate aerosols should be performed in a biological safety cabinet. Cylindrical electric burners are preferable to flame burners for sterilizing inoculating loops or needles and the tips of other small instruments. If flame burners are used, care should be taken to avoid spattering. This can be achieved by slowly drawing loops or needles through the flame with the loop entering the flame last. Cool inoculating loops and needles should be used when touching plates, colonies, or broth cultures. Work surfaces should be decontaminated at least once a day with an acceptable germicide. Work surfaces also should be decontaminated after spills (discussed later). Infectious wastes and patients' specimens should be disinfected before disposal (see later herein). Needles, blades, and other sharp items should be disposed of in rigid, tamper-resistant, puncture-proof, marked containers. Materials removed from the laboratory should be free of infectious hazard. Clinical specimens, cultures, or other potentially infectious materials should be packaged, labeled, and shipped according to federal regulations [39,85].
Safety Procedure Manual
Every laboratory should have an up-to-date safety manual that includes the following information:
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Safety in Handling Accidents, Using Equipment, and Disposing of Wastes
Procedures for Spills and Accidents
Because of the potential for high concentration of microorganisms in patients' specimens and cultures in clinical laboratories, special procedures must be used to disinfect spills and other laboratory accidents [39,84]. The current CDC recommendation is to use “chemical germicides that are approved for use as ‘hospital germicides’ and are tuberculocidal when used at recommended dilutions” [50,63]. This recommendation applies to all types of spills or other laboratory accidents.
Written procedures should be in the laboratory safety manual. Employees should be trained to safely decontaminate and clean up spills involving those microorganisms cultured or studied in their laboratory. All necessary disinfectants and cleaning supplies must be readily available in the laboratory. Because spills may occur at any stage of transport, plating, processing, or storage of microbiological cultures, specific protocols should be available for spills occurring at each stage and for spills involving common-place moderate-risk microorganisms and those of higher risk, such as M. tuberculosis.
The hazard associated with a spill depends on the nature of the spilled agent, the volume of material spilled, the concentration of the agent within the material, and where the spill takes place. Spills involving microorganisms such as M. tuberculosis, F. tularensis, Brucella spp, C. immitis, or H. capsulatum may pose a major hazard to laboratory workers. Spills of large volumes of moderate-risk microorganisms or those occurring in such a manner that aerosols might be generated also should be treated as a major hazard to laboratory workers.
Procedures Used for Routine Spills of Small Volumes of Moderate-Risk Microorganisms
Procedures for Spills of Large Volumes of Moderate-Risk Agents or Highly Pathogenic Agents Outside a Biological Safety Cabinet
Procedures for Spills in Biological Safety Cabinets
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Laboratory Equipment
Laboratory safety and diagnostic equipment must be of the proper type and should be tested and maintained according to the manufacturer's recommendations. Equally important is its proper use by laboratory personnel. All personnel should be instructed on the proper use, care, and maintenance of laboratory equipment.
Biological Safety Cabinets
Biological safety cabinets are essential for the safe handling of infectious agents. Different BSCs are available; which one to use depends primarily upon the infectious agents to be handled [86]. Class I BSCs (Figure 22-1) have an open front into which room air flows. All of the exhaust air is discharged through HEPA filters to the outside environment. Although Class I BSCs protect the user from exposure to agents within the cabinet, they do not protect materials within the cabinet against contamination; Class I BSCs are unsuitable for use in clinical microbiology laboratories [39].
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Figure 22-1 Design of class I biological safety cabinet |
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Figure 22-2 Design of class II biological safety cabinets types A and B |
Class II BSCs (Figure 22-2) also have an open front into which room air flows. These BSCs differ from Class I BSCs in that a portion of the exhausted air passing through HEPA filters is recirculated into the cabinet. Then the filtered air is used to protect clinical specimens or cultures from contamination. Two basic types of Class II BSCs are available. Class II type A BSCs are the most commonly used in clinical laboratories and are sufficient for meeting biosafety level 2 or 3 criteria. Class II type B BSCs also may be used for this purpose but usually are more expensive to purchase and to operate [39,86]. Class III (Figure 22-3) BSCs provide the greatest protection to laboratory personnel, but their use usually is restricted to working with highly virulent pathogens in biosafety level 4 laboratories.
Laboratory workers must remember that BSCs are not chemical fume hoods. Toxic, noxious, or flammable chemicals must not be used in these hoods because the recirculation of exhaust air may allow these chemicals to reach dangerously high levels in the cabinet. BSCs should be installed, tested, and maintained only by qualified personnel. Regular testing and certification of BSCs is essential to ensure the safety of users. Laboratory personnel should be instructed in the proper use of BSCs and should be aware of their limitations in controlling aerosols. Personnel working in BSCs can adversely affect the ability of cabinets to contain infectious aerosols [82]. Users should consult the manufacturer on the potential effect of this and other factors (e.g., use of equipment within BSCs) before using a BSC. Finally, personnel should be aware that cabinet function depends on proper airflow patterns and that change in airflow patterns because of alterations in air supplies, temporary shutdowns for repairs, and so on, may adversely affect the functioning of BSCs.
Centrifuges
Centrifuges used to process clinical specimens or cultures should be equipped with sealable, autoclavable, breakage-resistant cups to prevent contamination of the centrifuge and the release of aerosols should centrifuge tubes break during processing. These cups must be removable from the centrifuge rotor so that they can be cleaned and autoclaved.
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Autoclaves
An autoclave should be readily accessible to clinical laboratories. Routine maintenance, testing, and cleaning are essential. Autoclaves should be tested for their ability to kill standard bacterial spores [39]. It should be emphasized that autoclave tape indicates that an object has been autoclaved but not necessarily sterilized [83,84].
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Figure 22-3 Design of class III biological safety cabinet |
Laboratory and Protective Equipment
Other laboratory equipment should be of a type and design that allows for easy cleaning and disinfection. Safety equipment for the cleanup and disinfection of laboratory spills should be readily available. Proper gloves, gowns, masks, and shoe covers should be handy.
Both latex and vinyl disposable gloves have been shown to vary widely in their permeability [78,80]. It has been found that washing and reusing gloves is inadvisable and that the proportion of hands contaminated with test microorganisms after gloves are removed varies from 5%–50% [79]. Therefore, HCWs should wash their hands/perform hand hygiene after removing gloves. The issue of wearing two pairs of gloves (“double-gloving”) is more contentious. Although it is logical to assume that two barriers offer more protection than one, concerns about loss of tactile sensation and dexterity have led to recommendations against double-gloving during routine laboratory procedures [80]. Wearing two pairs of gloves for autopsies and in other situations where large amounts of blood are present has been recommended [38].
Disposal of Infectious Materials
Materials contaminated with infectious agents must be disposed of properly to protect HCWs and the general public [39,83]. Safe disposal of infectious materials begins at the source where these materials are generated. The following procedures are recommended for the safe disposal of infectious materials and waste [39,83]:
Prevention, Postexposure Treatment, and Follow-Up
Vaccination
Laboratory workers may or may not have contact with patients, but they should still follow recommendations regarding vaccinations for all HCWs. All HCWs should be vaccinated against HBV. If possible, such vaccination should be given during the training years because the risk of occupational exposure to HBV appears to be greatest
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during that period. In addition, before employment, all HCWs should provide evidence of immunity to rubella. Persons lacking protective antibody to rubella virus should be vaccinated. Influenza, measles, mumps, and polio vaccines and tetanus-diphtheria toxoid immunization should comply with current guidelines from the Advisory Committee on Immunization Practices of the U.S. Public Health Service (see Chapter 4).
Postexposure Treatment and Prophylaxis
Specific treatment, prophylaxis, and counseling should be available for all HCWs after exposure to infectious agents. Of special importance to clinical laboratory workers are recommendations for prophylaxis or treatment of exposures to specimens taken from patients who are infected with HBV, HCV, or HIV. HCWs working in the mycobacteriology laboratories and those involved in the processing or disposal of materials likely to be contaminated with mycobacteria should receive pre-employment screening for M. tuberculosisand appropriate testing following a suspected exposure. The reader is referred to Chapter 4 for additional information.
Postexposure Investigation
Laboratory exposure of a HCW to a pathogen should prompt an immediate investigation into the reason(s) for the exposure. The investigation should include a review of relevant microbiologic practices, laboratory policies and procedures, and equipment and facilities. For example, when an HCW who works with mycobacteria has a tuberculin skin test conversion or develops active pulmonary TB, the BSC and air-handling systems should be checked, serviced, and balanced by qualified personnel. If the investigation does not provide a satisfactory explanation for the source of the exposure, it may be necessary to broaden the investigation. Using the same example, an HCW who works with mycobacteria but has other responsibilities outside the laboratory (e.g., phlebotomy) could conceivably have been exposed to a patient with active TB. If no source of exposure is found, the investigation should be expanded as appropriate to include potential sources of exposure outside the healthcare facility (e.g., family members).
Conclusions
Although the incidence of laboratory-acquired infections appears to be declining, infections still occur at a low rate and are associated with significant morbidity and mortality. Infections caused by HBV or HIV are of particular concern. Laboratory personnel should make every attempt to follow recommended guidelines, policies, and procedures designed to minimize the risk of working with infectious materials. Each laboratory must be designed and constructed to minimize accidents and facilitate cleanups. It must contain proper and well-maintained safety and diagnostic equipment. Most important, however, is the proper training and supervision of laboratory personnel and adherence to policies and procedures designed to provide a safe working environment. It is the obligation of laboratory directors and administrators to provide such an environment.
References
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