BACKGROUND: The dangers of consuming unpasteurized milk are well documented. Numerous pathogens can contaminate raw milk and may subsequently cause illness, disease, and death. The majority of outbreaks involving unpasteurized dairy products have been caused by Campylobacter spp. followed by Shiga toxin–producing Escherichia coli and Salmonella spp. Outbreaks of Cryptosporidium associated with unpasteurized cow milk have not been well described. Instead, cryptosporidiosis is most often associated with recreational water. We characterize a Cryptosporidium outbreak associated with the consumption of unpasteurized cow milk.
METHODS: The New Mexico Department of Health initiated a multi-agency investigation on September 13, 2016 after 3 laboratory-confirmed cases of cryptosporidiosis associated with raw cow milk consumption were identified from routine case investigations. A supplemental questionnaire was developed to collect detailed information on exposures to unpasteurized dairy products. Laboratory-confirmed Cryptosporidiumand epidemiologically-linked cases identified from June to December 2016 were interviewed. Stool and milk specimens were collected and sent to the Centers for Disease Control and Prevention (CDC) for polymerase chain reaction (PCR) testing and/or microscopy and molecular typing by restriction fragment length polymorphism (RFLP) and DNA sequencing.
RESULTS: In total, 7 cases (6 laboratory-confirmed, 1 epidemiologically-linked) that consumed unpasteurized milk from a local New Mexico dairy were identified. One cluster of 6 cases was identified with illness onset ranging from August 28-September 2, 2016. One additional outbreak-associated case with illness onset of November 24, 2016 was also identified. The ages ranged from 1 year-60 years old (median=32 years); 5 cases were male. Of the 4 stool specimens submitted to CDC, 3 were positive for Cryptosporidium parvum by conventional PCR and RFLP testing, 2 of which were subtyped as IIaA18G3R1. Unpasteurized milk produced prior to illness onset was unavailable for testing. No Cryptosporidiumwas detected from milk specimens produced at the dairy after illness onset of cases.
CONCLUSIONS: Epidemiologic evidence indicated unpasteurized milk as the likely source of the Cryptosporidium outbreak. Potential sources of infection other than unpasteurized milk were not identified. Molecular typing of stool specimens further supported the evidence. As milk produced prior to illness onset dates was not available for testing, it was not possible to show evidence of a milk contamination. Nonetheless, considering the increase in the number of outbreaks associated with unpasteurized dairy products, Cryptosporidium should be considered as a potential source of contamination of raw milk and unpasteurized milk associated outbreaks.