18 January 2012
On October 30, 2010, PulseNet, the national molecular subtyping network for foodborne disease surveillance, detected a multistate cluster of Salmonella Typhimurium infections with a particular pulsed-field gel electrophoresis (PFGE) pattern and other genetic characteristics, referred to here as strain X. In December, the New Mexico Department of Health identified 3 ill persons infected with strain X. One was a student and the 2 others were children of students in microbiology courses held at two different community college campuses. CDC collaborated with public health officials in several states to investigate this multistate cluster of Salmonella Typhimurium infections associated with exposure to clinical and teaching microbiology laboratories. Investigators used DNA analysis of Salmonella bacteria obtained through diagnostic testing to identify cases of illness that might be related.
Between August 20, 2010 and June 29, 2011, a total of 109 individuals infected with strain X of Salmonella Typhimurium were reported from 38 states.
In an epidemiologic study conducted during February and March 2011, 32 ill persons answered questions about exposures during the days before becoming ill. Investigators compared their responses with those of 64 persons of similar age previously reported to state health departments with other illnesses (controls). Preliminary analysis of this study suggested that exposure to clinical and teaching microbiology laboratories was a possible source of illness. Illnesses were identified among students in microbiology teaching laboratories and employees in clinical microbiology laboratories. Ill persons (60%) were significantly more likely than control persons (2%) to report exposure to a microbiology laboratory in the week before illness began. Additionally, multiple ill persons reported working specifically with Salmonella bacteria in microbiology laboratories. The New Mexico Department of Health found that the strain isolated from patients was indistinguishable by PFGE pattern from a commercially available Salmonella Typhimurium strain used in laboratory settings. This commercially available strain was known to be present in several teaching or clinical laboratories associated with ill students or employees infected with the outbreak strain. These data suggest this strain was the source of some of these illnesses. Additionally, several children who live in households with a person who worked or studied in a microbiology laboratory became ill with the outbreak strain.
See also: CDC Links Salmonella Outbreak to Lab Work