lab.jpgUsually, it is microbiology laboratories that are in the forefront of solving outbreaks, not being the likely vector. However, according to the CDC, as of April 20, 2011, a total of 73 individuals infected with the outbreak strain of Salmonella Typhimurium have been reported from 35 states: AK (1), AL (3), AZ (2), CA (1), GA (5), IA (1), ID (2), IL (3), IN (1), KS (1), KY (3), MA (2), MD (2), MI (2), MN (4), MO (2), NC (1), ND (1), NE (2), NJ (2), NM (3), NV (1), NY (1), OH (1), OK (1), OR (1), PA (6), SC (2), SD (1), TN (2), TX (1), UT (3), WA (5), WI (3), WY (1). Among persons with available information, illness onset dates range from August 20, 2010 to March 8, 2011. Infected individuals range in age from less than 1 year to 91 years-old, and the median age is 24 years-old. Sixty-three percent of patients are female. Fourteen percent of patients have been hospitalized. One death has been reported.

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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 to those of 64 persons of similar age previously reported to state health departments with other illnesses (controls). Preliminary analysis of this study has suggested exposure to clinical and teaching microbiology laboratories is a possible source of illness. Illnesses have been 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 the illness began. Additionally, multiple ill persons reported working specifically with Salmonella bacteria in microbiology laboratories. The New Mexico Department of Health found that the outbreak strain was indistinguishable 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 is the source of some of these illnesses. Additionally, several children who live in households with a person who works or studies in a microbiology laboratory have become ill with the outbreak strain.

So, how did this happen?