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Section VII

Agent Summary Statements

AGENT: Bacillus anthracis

Forty (40) cases of laboratory-associated anthrax, occurring primarily at facilities conducting anthrax research, have been reported (66, 151). No laboratory-associated cases of anthrax have been reported in the United States since the late 1950's when human anthrax vaccine was introduced.

Naturally and experimentally infected animals pose a potential risk to laboratory and animal care personnel.

LABORATORY HAZARDS: The agent may be present in blood, skin lesion exudates, cerebrospinal fluid, pleural fluid, sputum, and rarely, in urine and feces. Direct and indirect contact of the intact and broken skin with cultures and contaminated laboratory surfaces, accidental parenteral inoculation, and rarely, exposure to infectious aerosols are the primary hazards to laboratory personnel.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities using clinical materials and diagnostic quantities of infectious cultures. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for studies utilizing experimentally infected laboratory rodents. A licensed vaccine is available through the Centers for Disease Control and Prevention; however, immunization of laboratory personnel is not recommended unless frequent work with clinical specimens or diagnostic cultures is anticipated (e.g., animal disease diagnostic laboratory). Biosafety Level 3 practices, containment equipment and facilities are recommended for work involving production volumes or concentrations of cultures, and for activities which have a high potential for aerosol production. In these facilities immunization is recommended for all persons working with the agent, all persons working in the same laboratory room where the cultures are handled, and persons working with infected animals.

AGENT: Bordetella pertussis

Bordetella pertussis, a human respiratory pathogen of worldwide distribution, is the causative agent of whooping cough. The disease is typically a childhood illness; however, the agent has been associated, with increased frequency, in adult illness (106, 112, 130). Several outbreaks in health-care workers have been reported in the literature (106, 112). Adolescents and adults with atypical or undiagnosed disease can serve as reservoirs of infection and transmit the organism to infants and children (135). Eight cases of infection with B. pertussis in adults have been documented at a large research institution. The individuals involved did not work directly with the organism, but had access to common laboratory spaces where the organism was manipulated. One case of secondary transmission to a family member was documented (122). A similar incident occurred at a large midwestern university resulting in two documented cases of laboratory-acquired infection and one documented case of secondary transmission (146). Other laboratory-acquired infections with B. pertussis have been reported, as well as adult-to-adult transmission in the workplace (19, 35). Laboratory-acquired infections resulting from the manipulation of clinical specimens or isolates have not been reported. The attack rate of this airborne infection is influenced by intimacy and frequency of exposure of susceptible individuals.

LABORATORY HAZARDS: The agent may be present in respiratory secretions, but is not found in blood or tissues. Since the natural mode of transmission is by the respiratory route, the greatest potential hazard is aerosol generation during the manipulation of cultures or concentrated suspensions of the organism.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment, and facilities are recommended for all activities involving the use or manipulation of known or potentially infectious clinical materials or cultures. Animal Biosafety Level 2 should be used for the housing of infected animals. Primary containment devices and equipment (e.g., biological safety cabinets, centrifuge safety cups, or specially designed safety centrifuges) should be used for activities likely to generate potentially infectious aerosols. Biosafety Level 3 practices, procedures, and facilities are appropriate when engaged in large scale production operations. The current pertussis vaccine may not provide complete and permanent immunity; however, a booster dose of pertussis vaccine is not recommended for use in persons who have passed their seventh birthday (50).

AGENT: Brucella (B. abortus, B. canis, B. melitensis, B. suis)

B. abortus, B. canis, B. melitensis, and B. suis have all caused illness in laboratory personnel (129, 151, 176). Brucellosis is the most commonly reported laboratory-associated bacterial infection (127, 143, 151). Hypersensitivity to Brucella antigens is also a hazard to laboratory personnel. Occasional cases have been attributed to exposure to experimentally and naturally infected animals or their tissues.

LABORATORY HAZARDS: The agent may be present in blood, cerebrospinal fluid, semen, and occasionally urine. Most laboratory-associated cases have occurred in research facilities and have involved exposure to Brucella organisms being grown in large quantities. Cases have also occurred in a clinical laboratory setting: direct skin contact with cultures or with infectious clinical specimens from animals (e.g., blood, uterine discharges) are commonly implicated in these cases. Aerosols generated during laboratory procedures have caused large outbreaks (95). Mouth pipetting, accidental parenteral inoculations, and sprays into eyes, nose and mouth have also resulted in infection.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices are recommended for activities with clinical specimens of human or animal origin containing or potentially containing pathogenic Brucella spp. Biosafety Level 3 and Animal Biosafety Level 3 practices, containment equipment and facilities are recommended, respectively, for all manipulations of cultures of the pathogenic Brucella spp. listed in this summary, and for experimental animal studies. Vaccines are not available for use in humans.

AGENT: Campylobacter (C. jejuni/C. coli, C. fetus subsp. fetus)

C. jejuni/C. coli gastroenteritis is rarely a cause of laboratory associated illness. Three laboratory-acquired cases have been documented (138, 149, 155). Numerous domestic and wild animals, including poultry, pets, farm animals, laboratory animals, and wild birds are known reservoirs and are a potential source of infection for laboratory and animal care personnel. Experimentally infected animals are also a potential source of infection (155).

LABORATORY HAZARDS: Pathogenic campylobacters may occur in fecal specimens in large numbers. C. fetus subsp. fetus may also be present in blood, exudates from abscesses, tissues, and sputa. Ingestion or parenteral inoculation of C. jejuni constitute the primary laboratory hazards. The oral ingestion of 500 organisms caused infection in one individual (163). The importance of aerosol exposure is not known.

RECOMMENDED PRECAUTIONS: Biosafety level 2 practices, containment equipment and facilities are recommended for activities with cultures or potentially infectious clinical materials. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with naturally or experimentally infected animals. Vaccines are not available for use in humans.

AGENT: Chlamydia psittaci, C. pneumoniae, C. trachomatis

Infections with psittacosis, lymphogranuloma venereum (LGV), and trachoma are documented hazards and among the most commonly reported laboratory-associated bacterial infection. In one report, (151) the majority of cases were psittacosis, occurred before 1955, and had the highest case fatality rate of all groups of infectious agents. Additional cases of laboratory-acquired psittacosis have been documented more recently (127). Contact with and exposure to infectious aerosols in the handling, care, or necropsy of naturally or experimentally infected birds are the major sources of laboratory-associated psittacosis. Infected mice and eggs are less important sources of C. psittaci. Laboratory animals are not a reported source of human infection with C. trachomatis.

LABORATORY HAZARDS: C. psittaci may be present in the tissues, feces, nasal secretions and blood, of infected birds and in blood, sputum, and tissues of infected humans. C. trachomatis may be present in genital, bubo, and conjunctival fluids of infected humans. Exposure to infectious aerosols and droplets, created during the handling of infected birds and tissues, are the primary hazards to laboratory personnel working with psittacosis. The primary laboratroy hazards of C. trachomatis are accidental parenteral inoculation and direct and indirect exposure of mucous membranes of the eyes, nose, and mouth to genital, bubo, or conjunctival fluids, cell culture materials, and fluids from infected eggs. Infectious aerosols may also pose a potential source of infection.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities involving the necropsy of infected birds and the diagnostic examination of tissues or cultures known or potentially infected with C. psittaci or C. trachomatis. Wetting the feathers of infected birds with a detergent-disinfectant prior to necropsy can appreciably reduce the risk of aerosols of infected feces and nasal secretions on the feathers and external surfaces of the bird. Animal Biosafety Level 2 practices, containment equipment and facilities and respiratory protection are recommended for personnel working with naturally or experimentally infected caged birds. Gloves are recommended for the necropsy of birds and mice, the opening of inoculated eggs, and when there is the likelihood of direct skin contact with infected tissues, bubo fluids, and other clinical materials. Additional primary containment and personnel precautions, such as those recommended for Biosafety Level 3, may be indicated for activities with high potential for droplet or aerosol production and for activities involving production quantities or concentrations of infectious materials. Vaccines are not available for use in humans.

AGENT: Clostridium botulinum

While there is only one report (177) of botulism associated with the handling of the agent or toxin in the laboratory or working with naturally or experimentally infected animals, the consequences of such intoxications must still be considered quite grave.

LABORATORY HAZARDS: C. botulinum or its toxin may be present in a variety of food products, clinical materials (serum, feces) and environmental samples (soil, surface water). Exposure to the toxin of C. botulinum is the primary laboratory hazard. The toxin may be absorbed after ingestion or following contact with the skin, eyes, or mucous membranes, including the respiratory tract (93). Accidental parenteral inoculation may also represent a significant exposure to toxin. Broth cultures grown under conditions of optimal toxin production may contain 2,000,000 mouse LD(50) per mL (177).

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities with materials known or potentially containing the toxin. A pentavalent (ABCDE) botulism toxoid is available through the Centers for Disease Control and Prevention, as an investigational new drug (IND). This toxoid is recommended for personnel working with cultures of C. botulinum or its toxins. Solutions of sodium hypochlorite (0.1%) or sodium hydroxide (0.1N) readily inactivate the toxin and are recommended for decontaminating work surfaces and spills of cultures or toxin. Additional primary containment and personnel precautions, such as those recommended for Biosafety Level 3, are indicated for activities with a high potential for aerosol or droplet production, and those involving production quantities of toxin. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for diagnostic studies and titration of toxin.

AGENT: Clostridium tetani

Although the risk of infection to laboratory personnel is negligible, Pike (151) has recorded 5 incidents related to exposure of personnel during manipulation of the toxin.

LABORATORY HAZARDS: Accidental parenteral inoculation and ingestion of the toxin are the primary hazards to laboratory personnel. It is uncertain if tetanus toxin can be absorbed through mucous membranes; consequently, the hazards associated with aerosols and droplets remain unclear.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities involving the manipulation of cultures or toxin. While the risk of laboratory-associated tetanus is low, the administration of an adult diphtheria-tetanus toxoid at 10-year intervals further reduces the risk to laboratory and animal care personnel of toxin exposures and wound contamination, and is therefore highly recommended (32).

AGENT: Corynebacterium diphtheria

Laboratory-associated infections with C. diphtheria are documented. Pike (151) lists 33 cases reported in the world literature. Laboratory animal-associated infections have not been reported.

LABORATORY HAZARDS: The agent may be present in exudates or secretions of the nose, throat (tonsil), pharynx, larynx, wounds, in blood, and on the skin. Inhalation, accidental parenteral inoculation, and ingestion are the primary laboratory hazards.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities utilizing known or potentially infected clinical materials or cultures. Animal Biosafety Level 2 facilities are recommended for studies utilizing infected laboratory animals. While the risk of laboratory-associated diphtheria is low, the administration of an adult diphtheria-tetanus toxoid at 10-year intervals may further reduce the risk to laboratory and animal care personnel of toxin exposures and work with infectious materials (32).

AGENT: Francisella tularensis

Tularemia is the third most commonly reported laboratory associated bacterial infection (151). Almost all cases occurred at facilities involved in tularemia research. Occasional cases have been related to work with naturally or experimentally infected animals or their ectoparasites. Although not reported, cases have occurred in clinical laboratories.

LABORATORY HAZARDS: The agent may be present in lesion exudate, respiratory secretions, cerebrospinal fluid, blood, urine, tissues from infected animals, and fluids from infected arthropods. Direct contact of skin or mucous membranes with infectious materials, accidental parenteral inoculation, ingestion, and exposure to aerosols and infectious droplets have resulted in infection. Cultures have been more commonly associated with infection than clinical materials and infected animals. The human 25% to 50% infectious dose is approximately 10 organisms by the respiratory route (16).

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with clinical materials of human or animal origin containing or potentially containing Francisella tularensis. Biosafety Level 3 and Animal Biosafety Level 3 practices, containment equipment and facilities are recommended, respectively, for all manipulations of cultures and for experimental animal studies. An investigational live attenuated vaccine (16) is available. It is recommended for persons working with the agent or infected animals, and for persons working in or entering the laboratory or animal room where cultures or infected animals are maintained.

AGENT: Leptospira interrogans - all serovars

Leptospirosis is a well-documented laboratory hazard. Pike (151) reported 67 laboratory-associated infections and 10 deaths, and three additional cases have been reported elsewhere (127).

An experimentally infected rabbit was identified as the source of an infection with L. interrogans serovar icterohemorrhagiae (159). Direct and indirect contact with fluids and tissues of experimentally or naturally infected mammals during handling, care, or necropsy is a potential source of infection. In animals with chronic kidney infections, the agent is shed in the urine in enormous numbers for long periods of time.

LABORATORY HAZARDS: The agent may be present in urine, blood, and tissues of infected animals and humans. Ingestion, accidental parenteral inoculation, and direct and indirect contact of skin or mucous membranes with cultures or infected tissues or body fluids -- especially urine -- are the primary laboratory hazards. The importance of aerosol exposure is not known.

RECOMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities involving the use or manipulation of known or potentially infectious tissues, body fluids, and cultures, and for the housing of infected animals. Gloves are recommended for the handling and necropsy of infected animals, and when there is the likelihood of direct skin contact with infectious materials. Vaccines are not available for use in humans.

AGENTS: Legionella pneumophila; other Legionella-like agents

A single documented nonfatal laboratory-associated case of legionellosis due to presumed aerosol or droplet exposure during animal challenge studies with Pontiac Fever agent (L. pneumophila) has been recorded (24). Human-to-human spread has not been documented.

Experimental infections are readily produced in guinea pigs and embryonated chicken eggs (121). Challenged rabbits develop antibodies but not clinical disease. Mice are refractory to parenteral exposure. Unpublished studies by Kaufmann, Feeley and others at the Centers for Disease Control and Prevention have shown that animal-to-animal transmission did not occur in a variety of experimentally infected mammalian and avian species.

LABORATORY HAZARDS: The agent may be present in pleural fluid, tissue, sputum, and environmental sources (e.g., cooling tower water). Because the natural mode of transmission appears to be airborne, the greatest potential hazard is the generation of aerosols during the manipulation of cultures or of other materials containing high concentrations of infectious microorganisms (e.g., infected yolk sacs and tissues).

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities involving the use or manipulation of known or potentially infectious clinical materials or cultures, and for the housing of infected animals. Biosafety Level 3 practices with primary containment devices and equipment (e.g., biological safety cabinets, centrifuge safety cups) are used for activities likely to generate potentially infectious aerosols and for activities involving production quantities of microorganisms. Vaccines are not available for use in humans.

AGENT: Mycobacterium leprae

Inadvertent parenteral human to human transmission of leprosy following an accidental needle stick in a surgeon (115) and the use of a presumably contaminated tattoo needle (147) have been reported. There are no cases reported as a result of working in a laboratory with biopsy or other clinical materials of human or animal origin. While naturally occurring leprosy or leprosy-like diseases have been reported in armadillos (189) and in nonhuman primates (63, 126) humans are the only known important reservoir of this disease.

LABORATORY HAZARDS: The infectious agent may be present in tissues and exudates from lesions of infected humans and experimentally or naturally infected animals. Direct contact of the skin and mucous membranes with infectious materials, and accidental parenteral inoculation, are the primary laboratory hazards associated with handling infectious clinical materials.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities with known or potentially infectious clinical materials from infected humans and animals. Extraordinary care should be taken to avoid accidental parenteral inoculation with contaminated sharp instruments. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for animal studies utilizing rodents, armadillos, and nonhuman primates.

AGENT:Mycobacterium spp. other than M. tuberculosis, M. bovis or M. leprae

Pike reported 40 cases of nonpulmonary "tuberculosis" thought to be related to accidents or incidents in the laboratory or autopsy room (151). Presumably these infections were due to mycobacteria other than M. tuberculosis or M. bovis. A number of mycobacteria which are ubiquitous in nature are associated with diseases, other than tuberculosis or leprosy, in humans, domestic animals, and wildlife. Characteristically, these organisms are infectious but not contagious. Clinically, the diseases associated with infections by these "atypical" mycobacteria can be divided into three general categories:

LABORATORY HAZARDS: The agents may be present in sputa, exudates from lesions, tissues, and in environmental samples (e.g., soil and water). Direct contact of skin or mucous membranes with infectious materials, ingestion, and accidental parenteral inoculation are the primary laboratory hazards associated with clinical materials and cultures. Infectious aerosols, created during the manipulation of broth cultures or tissue homogenates of these organisms associated with pulmonary disease, also pose a potential infection hazard to laboratory personnel.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with clinical materials and cultures of Mycobacterium spp. other than M. tuberculosis or M. bovis. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for animal studies with mycobacteria other than M. tuberculosis, M. bovis, or M. leprae.

AGENT:Mycobacterium tuberculosis, M. bovis

Mycobacterium tuberculosis and M. bovis infections are a proven hazard to laboratory personnel as well as others who may be exposed to infectious aerosols in the laboratory (79, 127, 131, 151, 154). The incidence of tuberculosis in laboratory personnel working with M. tuberculosis has been reported to be three times higher than those not working with the agent (156). Naturally or experimentally infected nonhuman primates are a proven source of human infection (e.g., the annual tuberculin conversion rate in personnel working with infected nonhuman primates is about 70/10,000 compared with less than 3/10,000 in the general population) (102). Experimentally infected guinea pigs or mice do not pose the same problem since droplet nuclei are not produced by coughing in these species; however, litter from infected animals may become contaminated and serve as a source of infectious aerosols.

LABORATORY HAZARDS: Tubercle bacilli may be present in sputum, gastric lavage fluids, cerebrospinal fluid, urine, and in lesions from a variety of tissues (6). Exposure to laboratory-generated aerosols is the most important hazard encountered. Tubercle bacilli may survive in heat-fixed smears1, and may be aerosolized in the preparation of frozen sections and during manipulation of liquid cultures. Because of the low infective dose of M. tuberculosis for humans (i.e., ID(50) (10 bacilli) (160, 161) and in some laboratories a high rate of isolation of acid-fast organisms from clinical specimens (>10%), (77) sputa and other clinical specimens from suspected or known cases of tuberculosis must be considered potentially infectious and handled with appropriate precautions.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are required for activities at American Thoracic Society (ATS) laboratory level I, (3, 4) preparation of acid-fast smears, and culturing of sputa or other clinical specimens, provided that aerosol generating manipulations of such specimens are conducted in a Class I or II biological safety cabinet. Liquification and concentration of sputa for acid-fast staining may also be conducted safely on the open bench by first treating the specimen (in a Class I or II safety cabinet) with an equal volume of 5% sodium hypochlorite solution (undiluted household bleach) and waiting 15 minutes before centrifugation (142, 174).

Biosafety Level 3 practices, containment equipment and facilities are required for laboratory activities of ATS levels II and III) (3, 4) in the propagation and manipulation of cultures of M. tuberculosis or M. bovis, and for animal studies utilizing nonhuman primates experimentally or naturally infected with M. tuberculosis or M. bovis. Animal studies utilizing guinea pigs or mice can be conducted at Animal Biosafety Level 3. Skin testing with purified protein devivatie (PPD) of previously skin-tested-negative laboratory personnel can be used as a surveillance procedure. A licensed attenuated live vaccine (BCG) is available but is not routinely ued in the United States for laboratory personnel.

AGENT: Neisseria meningitidis

Meningococcal meningitis is a demonstrated but rare hazard to laboratory workers (8, 49, 153).

LABORATORY HAZARDS: The agent may be present in pharyngeal exudates, cerebrospinal fluid, blood, and saliva. Parenteral inoculation, droplet exposure of mucous membranes, infectious aerosol and ingestion are the primary hazards to laboratory personnel.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities utilizing known or potentially infectious body fluids, tissues, and cultures. Additional primary containment and personnel precautions such as those described for Biosafety Level 3, may be indicated for activities with high potential for droplet or aerosol production, and for activities involving production quantities or concentrations of infectious materials. The use of licensed polysaccharide vaccines (27) should be considered for personnel regularly working with large volumes or high concentrations of infectious materials.

AGENT: Pseudomonas pseudomallei

Two laboratory-associated cases of melioidosis are reported: one associated with a massive aerosol and skin exposure; (78) the second resulting from an aerosol created during the open-flask sonication of a culture presumed to be Ps. cepacia (166a).

LABORATORY HAZARDS: The agent may be present in sputum, blood, wound exudates and various tissues depending on the infection's site of localization. Direct contact with cultures and infectious materials from humans, animals, or the environment, ingestion, autoinoculation, and exposure to infectious aerosols and droplets are the primary laboratory hazards. The agent has been demonstrated in blood, sputum, and abscess materials and may be present in soil and water samples from endemic areas.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities utilizing known or potentially infectious body fluids, tissues, and cultures. Gloves should be worn when handling infected animals, during their necropsy, and when there is the likelihood of direct skin contact with infectious materials. Additional primary containment and personnel precautions, such as those described for Biosafety Level 3, may be indicated for activities with a high potential for aerosol or droplet production, and for activities involving production quantities or concentrations of infectious materials.

AGENT: Salmonella - all serotypes except typhi

Salmonellosis is a documented hazard to laboratory personnel (80, 127, 151). Primary reservoir hosts include a broad spectrum of domestic and wild animals, including birds, mammals, and reptiles, all of which may serve as a source of infection to laboratory personnel.

LABORATORY HAZARDS: The agent may be present in feces, blood, urine, and in food, feed, and environmental materials. Ingestion or parenteral inoculation are the primary laboratory hazards. The importance of aerosol exposure is not known. Naturally or experimentally infected animals are a potential source of infection for laboratory and animal care personnel, and for other animals.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with clinical materials and cultures known or potentially containing the agents. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with experimentally or naturally infected animals.

AGENT: Salmonella typhi

Typhoid fever is a demonstrated hazard to laboratory personnel (13, 80, 153).

LABORATORY HAZARDS: The agent may be present in feces, blood, gallbladder (bile) and urine. Humans are the only known reservoir of infection. Ingestion or parenteral inoculation of the organism represent the primary laboratory hazards. The importance of aerosol exposure is not known.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities utilizing known or potentially infectious clinical materials and cultures. Biosafety Level 3 practices and procedures are recommended for activities likely to generate aerosols or for activities involving production quantities of organisms.

Licensed vaccines, which have been shown to protect 70-90% of recipients, may be a valuable adjunct to good safety practices in personnel regularly working with cultures or clinical materials which may contain S. typhi (13).

AGENT: Shigella spp.

Shigellosis is a demonstrated hazard to laboratory personnel with dozens of cases reported in the United States and Great Britain alone (79, 80, 97, 151). While outbreaks have occurred in captive nonhuman primates, humans are the only significant reservoir of infection. However, experimentally infected guinea pigs, other rodents, and nonhuman primates are also proven sources of infection.

LABORATORY HAZARDS: The agent may be present in feces, and rarely, in blood of infected humans or animals. Ingestion or parenteral inoculation of the agent are the primary laboratory hazards. The oral 25%-50% infectious dose of S. flexneri for humans is approximately 200 organisms (191). The importance of aerosol exposure is not known.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities utilizing known or potentially infectious clinical materials or cultures. Animal Biosafety Level 2 facilities and practices are recommended for activities with experimentally or naturally infected animals. Vaccines are not available for use in humans.

AGENT: Treponema pallidum

Syphilis is a documented hazard to laboratory personnel who handle or collect clinical material from cutaneous lesions. Pike lists 20 cases of laboratory-associated infection (151). Humans are the only known natural reservoir of the agent. Syphilis has been transmitted to laboratory personnel working with a concentrated suspension of T. pallidum obtained from an experimental rabbit orchitis (74). Hematogenous transfer of syphilis has occurred from the transfusion of a unit of fresh blood obtained from a patient with secondary syphilis. T. pallidum is present in the circulation during primary and secondary syphilis. The minimum number (LD(50)) of T. pallidum organisms needed to infect by subcutaneous injection is 23 (114). The concentration of T. pallidum in patients' blood during early syphilis, however, has not been determined.

No cases of laboratory animal-associated infections are reported; however, rabbit-adapted strains of T. pallidum (Nichols and possibly others) retain their virulence for humans.

LABORATORY HAZARDS: The agent may be present in materials collected from primary and secondary cutaneous and mucosal lesions and in blood. Accidental parenteral inoculation, contact of mucous membranes or broken skin with infectious clinical materials, and possibly infectious aerosols, are the primary hazards to laboratory personnel.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities involving the use or manipulation of blood or lesion materials from humans or infected rabbits. Gloves should be worn when there is a likelihood of direct skin contact with lesion materials. Periodic serological monitoring should be considered in personnel regularly working with infectious materials. Vaccines are not available for use in humans.

AGENT: Vibrionic enteritis (Vibrio cholerae, V. para-haemolyticus)

Vibrionic enteritis due to Vibrio cholerae or Vibrio parahaemolyticus is a documented but rare cause of laboratory-associated illness (153). Naturally and experimentally infected animals are a potential source of infection.

LABORATORY HAZARDS: All pathogenic vibrios may occur in feces. Ingestion of V. cholerae, and ingestion or parenteral inoculation of other vibrios constitute the primary laboratory hazard. The human oral infecting dose of V. cholerae in healthy non-achlorhydric individuals is approximately 1,000,000 organisms (111). The importance of aerosol exposure is not known. The risk of infection following oral exposure may be increased in achlorhydric individuals.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with cultures or potentially infectious clinical materials. Animal Biosafety Level 2 practices, containment equipment and facilities are recommended for activities with naturally or experimentally infected animals. Although vaccines have been shown to provide partial protection of short duration (3-6 months) to nonimmune individuals in highly endemic areas,13 the routine use of cholera vaccine in laboratory staff is not recommended.

AGENT: Yersinia pestis

Plague is a proven but rare laboratory hazard. Four cases have been reported in the United States (17, 151).

LABORATORY HAZARDS: The agent may be present in bubo fluid, blood, sputum, cerebrospinal fluid (CSF), feces, and urine from humans, depending on the clinical form and stage of the disease. Primary hazards to laboratory personnel include: direct contact with cultures and infectious materials from humans or rodents; infectious aerosols or droplets generated during the manipulation of cultures, infected tissues, and in the necropsy of rodents; accidental autoinoculation; ingestion; and bites by infected fleas collected from rodents.

RECOMMENDED PRECAUTIONS: Biosafety Level 2 practices, containment equipment and facilities are recommended for all activities involving the handling of potentially infectious clinical materials and cultures. Special care should be taken to avoid the generation of aerosols from infectious materials, and during the necropsy of naturally or experimentally infected rodents. Gloves should be worn when handling field-collected or infected laboratory rodents, and when there is the likelihood of direct skin contact with infectious materials. Necropsy of rodents is ideally conducted in a biological safety cabinet. Although field trials have not been conducted to determine the efficacy of a licensed inactivated vaccine, experience with this product has been favorable.22 Immunization is recommended for personnel working regularly with cultures of Y. pestis or infected rodents (34).

Additional primary containment and personnel precautions, such as those described for Biosafety Level 3, are recommended for activities with high potential for droplet or aerosol production, for work with antibiotic-resistant strains and for activities involving production quantities or concentrations of infectious materials.

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