Apr 29, 2011 (CIDRAP News) – The US Centers for Disease Control and Prevention (CDC) said yesterday that it and public health partners in several states are investigating a Salmonella Typhimurium outbreak linked to lab exposure that has so far sickened 73 people in 35 states.
The illnesses involve a commercially available Salmonella enterica serotype Typhimurium strain used in laboratories, and health officials believe students or lab employees may have carried the bacteria to their homes on contaminated lab coats, pens, notebooks, or other items. Several of the patients are children who live in households with a person who studies or works in a microbiology lab.
Illness onset dates for patients with available information range from Aug 20, 2010, to March 8, 2011. Ages range from less than 1 year to 91 years, with a median age of 24. Sixty-three percent of the patients are female; 14% of the patients were hospitalized, and one death has been reported.
The CDC said the number of new cases involving the outbreak strain has dropped over the past several months and that levels have returned to the expected baseline of 0 to 4 per week.
The epidemiologic investigation, conducted during February and March, that compared exposures of 32 of the outbreak patients with 64 controls who were sick with other illnesses found that exposure to clinical and teaching microbiology lab exposure was a possible illness source. Some of the sick patients were students or employees in the labs, many of whom reported working with Salmonella.
Investigation activities are ongoing, and the CDC said the American Society for Microbiology and the Association of Public Health Laboratories are surveying lab directors, managers, and faculty to identify areas were biosafety and training can be improved to avoid similar future infections.
The CDC advised lab students and workers to observe biosafety practices when working with agents such as Salmonella and to avoid bringing home pens, notebooks, and other items used inside the lab. It also warned against bringing food, drinks, and personal items such as car keys and cell phones into the labs where they can become contaminated.
Joshua Rounds, MPH, an epidemiologist with the Minnesota Department of Health, said one of the first clues was a case cluster in New Mexico, where state health officials found that the outbreak strain was indistinguishable from the Salmonella Typhimurium strain used in lab settings. He said the strain, commonly used as a control in testing, isn't known to be unusually pathogenic.
Rounds said infections from the lab strain have been seen before, though an outbreak spanning several states is unusual. He said it's unclear if the outbreak signifies an emerging threat or if increased use of multistate foodborne illness conference calls has led to a more uniform evaluation of exposure to the pathogen.
Apr 28 CDC outbreak notice