Lab workers face risk of deadly meningitis
Lab workers face risk of deadly meningitis
Lack of biosafety cabinet is a major risk factor
Although the exact mechanism of transmission is unclear, failure to use a biosafety cabinet during manipulation of sterile site isolates of Neisseria meningitidis threatens lab workers with an occupational infection that has a 50% mortality rate, the Centers for Disease Control and Prevention (CDC) reports.
"What we found that in nearly all of these cases involved manipulation of the isolate outside of a biosafety cabinet," says Jim Sejvar, MD, medical epidemiologist in the CDC’s meningitis and special pathogens branch. "We don’t understand enough about the transmission to say definitively that this is what causes the laboratory-acquired infections. But it certainly suggests that by manipulating these isolates outside of those enclosures, the laboratorians are putting themselves at greater risk."
Despite the deaths of two lab workers in Michi-gan and Alabama two years ago, the CDC decided not to officially recommend routine immunization of lab workers for N. meningitidis. While urging laboratorians to make "an informed decision" about immunization, the CDC is emphasizing laboratory safety measures with generated aerosols and drop-lets as the best method to prevent future cases.1
The primary problem is that the vaccine does not cover N. meningitidis serogroup B, which caused half of the fatal cases recently reviewed by the CDC. The vaccine currently available in the United States covers groups A, Y, and W-135 and C, the type of meningitis that killed the two laboratorians in 2000. In its recently published official report of the cases, the CDC concluded: "Although primary prevention should focus on laboratory safety, laboratory workers also should make informed decisions about vaccination. The quadrivalent meningococcal polysaccharide vaccine . . . will decrease but not eliminate the risk for infection. Research and industrial laboratory scientists who are exposed routinely to N. meningitidis in solutions that might be aerosolized also should consider vaccination. In addition, vaccination might be used as an adjunctive measure by microbiologists in clinical laboratories."
Two cases lead to 16 others
As previously reported in Hospital Infection Control, the unrelated cases shocked medical communities in Huntsville, AL, and Lansing, MI, because two experienced and highly regarded laboratorians died after occupational exposures to the pathogen. (See HIC, April 2001 under archives at www.HIConline.com.) The CDC found in investigating the two deaths that 16 previously unreported cases of probable N. meningitidis infection occurred in laboratories over the prior 15 years.
Of those, nine (56%) were caused by N. meningitidis serogroup B, and seven (44%) were caused by serogroup C. Overall, eight cases (50%) were fatal, three from serogroup B and five from serogroup C, the CDC reported.1
"[The vaccine] does not protect against sero-group B, which in this [report] was responsible for half of the laboratory-acquired cases," Sejvar says. "I think as opposed to focusing on vaccination as the primary method of prevention, we need to be focusing on laboratory safety. Anecdotally, of the laboratorians I have talked to, most of them are choosing to receive the vaccine. I think that is a very wise decision, but we felt that the more reasonable approach was to emphasize the laboratory safety issues and not the vaccine issues."
The identification of the previously unreported cases suggests that either cases of laboratory-acquired meningococcal disease are underreported or on the increase, the CDC concluded. In addition, the case-fatality rate of 50% is substantially higher than that observed among community-acquired cases. That might reflect underreporting of mild cases or might be a result of the highly virulent strains and high concentration of organisms encountered in the laboratory setting, the CDC speculated. Is there another group out there of less serious, unreported laboratory infections?
"We have no idea," he says. "That’s partially the issue. If anything, this is probably an underestimation. In general, where you do passive surveillance like this, you are going to catch the severe cases because they come to people’s attention."
In 15 of the 16 cases, the laboratory workers reportedly did not perform procedures within a biosafety cabinet. It appears that exposure to isolates of N. meningitidis — and not patient samples — increases the risk for infection. Nearly all the microbiologists were manipulating isolates and performing subplating with an inoculation loop on an open laboratory bench. N. meningitidis is classified as a biosafety level 2 organism.
Current lab guidelines do not recommend the routine use of a biosafety cabinet for isolate manipulation. A biosafety cabinet is recommended for mechanical manipulations of samples that have a "substantial risk" for droplet formation or aerosolization such as centrifuging, grinding, and blending, the CDC notes.
The nation’s major lab groups such as the Washington, DC-based American Society for Microbiology will discuss possible guideline revisions based on the findings, according to the CDC. In light of the cases, the CDC currently recommends that "if a biosafety cabinet or other means of protection is unavailable, manipulation of these isolates should be minimized, and workers should consider sending specimens to laboratories possessing this equipment."
The CDC recommends also that lab workers’ percutaneous exposure to an invasive N. meningitidis isolate from a sterile site should receive treatment with penicillin. Those with known mucosal exposure should receive antimicrobial chemoprophylaxis. (See table.)
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Schedule for Administering Chemoprophylaxis |
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Source: Centers for Disease Control and Prevention. Laboratory-Acquired Meningococcal Disease — United States, 2000. MMWR 2002 51:141-144. |
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Microbiologists who manipulate invasive N. meningitidis isolates in a manner that could induce aerosolization or droplet formation (including plating, subculturing, and serogrouping) on an open bench top and in the absence of effective protection from droplets or aerosols also should consider antimicrobial chemoprophylaxis. The CDC continues prospective surveillance for laboratory-acquired meningococcal disease. Hospitals, laboratories, and public health departments that are aware of suspected cases should report these cases through their state public health department to the CDC at (404) 639-3158.
Reference
1. Centers for Disease Control and Prevention. Laboratory-Acquired Meningococcal Disease — United States, 2000. MMWR 2002 51:141-144.
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