CDC urges caution for lab work with meningococcus

14 new cases found in labs, half of them fatal

Hospital laboratories are stepping up precautions for lab workers who handle meningococcal samples in the wake of two deaths in Michigan and Alabama.

Although the risk of death from handling Neisseria meningitidis isolates remains low, the Centers for Disease Control and Prevention (CDC) in Atlanta cautioned laboratory workers of this occupational hazard.1

An investigation into the deaths led CDC researchers to discover 14 previously unreported cases worldwide in the past 15 years. Six of those cases occurred in the United States between 1996 and 2001.

The fatality rate was high; lab workers died in half of the cases that researchers determined were probably laboratory-acquired meningoccal disease.

The higher-than-expected death rate "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 researchers state.

While the CDC has not changed its recommendations that N. meningitidis isolates be handled as a Biosafety Level 2, "strong consideration should be made to do all manipulations of this organism in a biosafety cabinet," says Jim Sejvar, MD, epidemiologist in the CDC’s meningitis and special pathogens branch.

"If [a safety cabinet] is not available or not able to be used, the organism should be transferred to a facility that does [have one]," he says. Vaccination should be considered as an "adjunctive measure," Sejvar says. The vaccine is effective against sero-groups A, C, Y, and W-135. "It doesn’t provide any protection against serogroup B, which was in fact represented in half of the U.S. cases that we saw," he says.

Lab workers followed CDC guidelines

Concerns about laboratory-acquired meningococcal disease arose in 2000 with the reports from Alabama and Michigan. Both involved experienced laboratory workers who were known for their careful technique. And in both cases, CDC testing confirmed that the strain was the same as the patient sample.

In the Alabama case, a 12-year-old girl came to a Huntsville hospital complaining of nausea, cough, headache, and high fever. She had some decreased alertness, and a physician ordered a lumbar puncture to test for meningitis.

The day after the hospital lab had taken the samples and cultured them, a laboratory worker came in to perform some additional tasks of subculturing, which he did in the containment hood, and removing additional blood samples for Gram stains — done outside a hood.

When the lab worker developed fever and joint aches three days later, it wasn’t immediately identified as possible meningitis. The next day, his symptoms of nausea, pain, lethargy, and weakness escalated and his body temperature dropped. He died within hours of coming to the hospital’s emergency department (ED).

The lab worker had followed recommended practices in handling the sample, notes state epidemiologist J.P. Lofgren, MD.

In the Michigan case, a longtime laboratory worker with the state Department of Community Health in Lansing was working with ear fluid from a 19-year-old Michigan State University student who had died of toxic shock syndrome. The ear fluid contained meningococcus, although the young woman did not have any symptoms of meningococcal infection.

Two days after working with the sample, the lab worker developed symptoms. The next day, she went to the ED with labored breathing and died hours later.

Biosafety Level 2 guidelines state that lab workers should wear gloves and lab coats and should use a biological safety cabinet when "mechanical manipulations that have high aerosol potential are performed." Workers who have a blood exposure should receive chemoprophylaxis with penicillin, and those with mucosal exposure should be treated with rifampin, according to the CDC.2

But just what types of procedures should be performed in a safety cabinet is somewhat unclear, Sejvar acknowledges. "Clearly, further research is needed to determine what the specific risk factors are," he says.

After the death, the Michigan Department of Community Health began treating meningococcus as a Level 3 organism, requiring lab work to occur under a biological containment hood with an air filter. Lab workers also were immunized. Alabama continues to follow current CDC guidelines.

Nationally, hospitals and public health laboratories encounter about 3,000 isolates of N. meningitidis each year. Since the clinical samples and isolates are handled by an average of three microbiologists in a laboratory investigation, CDC estimates that 9,000 microbiologists are exposed per year.

"The risk [of laboratory-acquired meningococcal disease] is still low," Sejvar says. "But as far as an occupational risk, laboratorians certainly seem to be much more at risk than people in general."

CDC is asking hospitals and laboratories to report any suspected cases of lab-acquired meningococcal disease through the state health department to CDC at (404) 639-3158.

References

1. Lofgren J, Whitley B, Johnson D, et al. Laboratory-acquired meningococcal disease —- United States, 2000. MMWR 2002; 51:141-144.

2. Takata KK, Hinton BG, Werner SB, et al. Epidemiologic notes and reports: Laboratory-acquired meningococcemia — California and Massachusetts. MMWR 1991; 40:46-47, 55.