This week’s Morbidity and Mortality Weekly Report (MMWR), a publication from the Centers for Disease Control and Prevention, contains an outbreak report on a Salmonella Typhimurium outbreak associated with the consumption of raw milk and cheese produced at a Pennsylvania dairy beginning in February, 2007.
According to the report, several people who consumed raw unpasteurized dairy products from the dairy became ill with Salmonellosis and the strain of Salmonella isolated from ill people’s stool was indistinguishable from that isolated from a bulk dairy tank at the dairy. In all, 29 cases of Salmonella were identified as part of the outbreak.
The Pennsylvania Department of Health findings regarding the Salmonella outbreak are summarized in the report:
A total of 29 cases were identified, with illness onset occurring in three temporal clusters during February 3–July 14, 2007 (Figure). The first cluster consisted of 15 cases with onsets of illness from February 3 to March 5. Raw-milk samples were collected February 20 from a dairy A bulk milk tank and February 28 from the home of an ill person. Both sets of samples yielded the outbreak strain of S. Typhimurium. On March 2, PDA ordered dairy A to stop raw-milk sales and advised the public not to consume raw-milk products from dairy A.
On March 19, PDA allowed dairy A to resume sales of raw milk after PDA conducted inspections and recorded two consecutive negative cultures from milk-tank samples. However, a second cluster of three cases was detected when the outbreak strain of S. Typhimurium was identified in another patient, whose diarrheal illness began on March 21 and who had consumed raw milk from dairy A after sales resumed. The two additional cases were identified in persons with onsets of illness on March 19 and March 22. The first of these occurred in one of six ill persons who primarily spoke Spanish and who told investigators they had not consumed raw milk. However, when reinterviewed in early April, three of these six persons reported consuming queso fresco (a type of soft cheese) they bought at a grocery store serving the local Hispanic community. PDA learned that the queso fresco had been made by an unlicensed producer who purchased approximately 20 gallons of raw milk weekly from dairy A. Sale of raw-milk cheeses aged <60 days is illegal in Pennsylvania. Subsequently, in April, PDA inspectors seized 18 unlabeled retail containers of queso fresco from the grocery store. The cheese tested positive for alkaline phosphatase, indicating the cheese was produced from unpasteurized milk (2). Bacterial cultures were negative for pathogens.
On March 27, PDA again ordered dairy A to halt raw-milk sales and suspended its raw-milk permit. No additional cases were noted until June–July 2007, when a third cluster of 11 PFGE-matched S. Typhimurium cases was detected through routine electronic laboratory reporting. Of these, 10 occurred among residents of three counties near dairy A. On July 19, PDA confirmed that dairy A had been distributing raw milk to the public despite its suspended permit; the date when illegal milk distribution began could not be determined. The outbreak strain of S. Typhimurium was isolated from dairy A raw milk collected from a bulk milk tank on July 19 and from the home of an ill person on July 20. PDA ordered dairy A to halt distribution of raw milk on July 20 and subsequently revoked the raw-milk permit for this dairy.