West Nile a new threat to laboratory workers
Two cases result from sharps injuries
West Nile virus is emerging as a new threat to laboratory workers as its presence grows in the United States. Infection control precautions should be reemphasized in light of two occupational cases of West Nile virus infection in research laboratorians, the Centers for Disease Control and Prevention (CDC) emphasizes.
"Both of these laboratory workers were working with materials that had high concentrations of West Nile virus in them, whereas people who are working in clinical labs are dealing generally with samples that have a very low likelihood of having high concentrations of West Nile virus," says Roy Campbell, MD, PhD, medical epidemiologist in the CDC vector-borne infections branch. "But the message for clinical laboratory workers is that you can get West Nile virus from laboratory accidents. They are uncommon, and your risk is much lower than the two laboratory workers that we describe, but it is not zero," he says.
West Nile virus, a mosquito-borne flavivirus introduced recently to North America, is a human, equine, and avian neuropathogen. The majority of human infections with West Nile virus are mosquito-borne.
Lab infections documented
However, laboratory-acquired infections with West Nile and arboviruses have occurred historically. The most recent reports came late last year in two separate incidents.
"One of them was a needlestick, and one was a scalpel injury," Campbell says. "One was working on an infected bird, and the other was working on infected mice. We didn’t conclude that there was any particular break in procedure."
In the first case, in August 2002, a microbiologist was performing a necropsy on a blue jay submitted as part of a state’s West Nile virus surveillance program. The microbiologist — working in a Class II laminar flow biosafety cabinet under biosafety level 2 conditions — lacerated a thumb while using a scalpel to remove the bird’s brain.
The superficial cut was cleansed and bandaged. Four days later the lab worker had acute symptoms of headache, myalgias, and malaise followed by chills, sweats, dysesthesias, recurring hot flashes, swelling of the post-auricular lymph nodes, and anorexia. Two days later, the microbiologist noted a maculopapular rash that began on the face. The rash extended to the trunk, arms, and legs during the next three days; and then disappeared gradually. The microbiologist continued to work during illness and had intermittent chills, sweats, dysesthesias, and hot flashes for approximately one week before recovering fully, the CDC reports.
The second case occurred in October 2002. A laboratorian who was harvesting West Nile-infected mouse brains in a Class II laminar flow biosafety cabinet under BSL-3 conditions punctured a finger with a contaminated needle. The wound was cleansed and bandaged. Three days after injury, the lab worker had upper respiratory infection symptoms without fever or chills. The next day, symptoms continued with malaise, fatigue, chills, and a low-grade fever. Although the worker missed only one day of work, respiratory symptoms, dry cough, and hoarseness continued for more than a week.
"We didn’t recommend any changes in lab workers based on these two cases. Both of these case involved laboratories following proper procedures. Sometimes, these things happen regardless of how many precautions you take.
Lab workers handling fluids or tissues known or suspected to be infected with West Nile virus should minimize their risk for exposure and should report injuries and illnesses of suspected occupational origin to their supervisor. Illnesses in both laboratory workers were mild and self-limited, which is typical of illnesses in WNV-infected persons. But the cases confirm that laboratory workers are at risk for occupationally-acquired WNV infection, including West Nile meningoencephalitis.
"There have been 18 cases [of lab-acquired West Nile virus] in the literature summarized in various review articles, the most recent of which was in 1980," Campbell says. Other cases may be on the horizon, because the number of laboratories and laboratory workers involved in arboviral diagnostic and reference activities has increased dramatically since West Nile emerged in the United States.
"More laboratories — be they clinical, research, or reference laboratories — are dealing with West Nile virus than ever before," Campbell says. "There is an unprecedented number of laboratories and laborationians working with West Nile virus in the United States," he says. "So it is not surprising to find a few cases like this. We don’t know if this is a trend or whether these cases will be very few and far between."
A universal or standard precautions approach with all specimens is the best protection for clinical lab workers, Campbell adds. "Anybody who is dealing with clinical lab specimens has to assume that those are infected with any number of agents, and West Nile virus would be one of the least of their worries, he says. "Every sample needs to be treated as if it were infectious."
Laboratory workers involved in necropsies or other procedures involving materials potentially infected with the virus should use every precaution to minimize their risk for exposure to fluids or tissues during handling, including standard droplet and contact precautions; using and disposing of needles, scalpels, and other sharp instruments safely; and minimizing the generation of aerosols.
Reference
1. Centers for Disease Control and Prevention. Laboratory-acquired West Nile virus infections —- United States. MMWR 2002; 51(50):1,133-1,135.
West Nile virus is emerging as a new threat to laboratory workers as its presence grows in the United States. Infection control precautions should be reemphasized in light of two occupational cases of West Nile virus infection in research laboratorians, the Centers for Disease Control and Prevention (CDC) emphasizes.
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