The Enteric Diseases programs at CDC have been collaborating with state public health officials, the USDA-Food Safety and Inspection Service, and the US Food and Drug Administration (FDA) to investigate a multi-state outbreak of human infections due to Salmonella serotype Typhimurium affecting almost 400 persons. There are numerous interesting features of this outbreak that highlight the complex issues I discussed recently for foodborne outbreaks. In this case, there was an early unrelated, but overlapping outbreak, several PulseNet patterns involved in the outbreak, a State Health Department being the first to pull the trigger for a product advisory, and a contaminated ingredient that is in many foods.
- Multiple concurrent outbreaks. Early in this outbreak there was a restaurant cluster of Salmonella Typhimurium illness in Ohio due to chicken. However, additional laboratory testing suggested that this cluster was a different strain of Salmonella Typhimurium from the outbreak strain.
- Multiple PulseNet patterns. The current national outbreak involves two closely related pulsed-field gel electrophoresis (PFGE) DNA patterns that would usually have been considered separate clusters. More sophisticated testing by multilocus variable number tandem repeat analysis (MLVA) confirmed that these clusters should be combined and treated as part of the same outbreak.
- Nothing beats a great epidemiologic investigation to complement the nifty laboratory testing. While CDC was conducting a national case-control study, a process where we compare what sick persons ate with what healthy persons ate, Minnesota health officials were conducting a similar study amongst their residents as well as collecting and testing various products the ill persons ate. Their results suggested King Nut Peanut Butter which is served in institutional settings.
- States must and do act independently from CDC. Based on their epidemiology study, Minnesota authorities first looked for and found Salmonella Typhimurium in a jar of peanut butter and instituted a product advisory for King Nut peanut butter. Although well-coordinated with federal authorities, they did not need to wait for the results of CDC’s case-control study or the FDA’s inspection of the plant to act to protect their residents.
- More to come…
Figure 1: Typhimurium Curve