Drinking Raw Milk: Worth the Risk?

Jennifer Garcia

December 11, 2013

The incidence of illness secondary to raw milk consumption is higher than previously recognized and highlights the need for more education in this area, according to a new study by the Minnesota Department of Health. The study findings were published online December 11 in Emerging Infectious Diseases.

Using surveillance data from the Minnesota Department of Health obtained between 2001 and 2010, Trisha J. Robinson, from the Minnesota Department of Health, St. Paul, and colleagues identified 6747 Campylobacter spp infections, 1742 Cryptosporidium spp infections, 1069 Shiga toxin–producing Escherichia coli (STEC) O157 infections, 354 non-O157 STEC infections, and 4427 Salmonella spp infections. Patients were interviewed regarding possible sources of infection, including raw milk consumption. Patients who declined to be interviewed, were part of an outbreak, or who had a recent history of international travel were excluded from the analysis (n = 6695).

Raw milk consumption was reported among 3.7% (530) of the 14,339 patients identified; 77% (407) of these were infected with Campylobacter spp, primarily C jejuni. Of those infected with STEC O157, 1.8% reported raw milk consumption, and "those reporting raw milk consumption had a median age of 5 years (range 11 months to 63 years), compared with a median age of 16 years (range 5 months to 92 years) among those who did not report raw milk consumption (p = 0.02)." Similarly, among the 3.4% of patients with non-O157 STEC infections and a history of raw milk consumption, the median age was 4 years (range, 1 - 63 years).

On the basis of population estimates, reported raw milk consumption data, and applying pathogen-specific multipliers to the 530 infections associated with raw milk consumption, the researchers estimate that 17.3% of people who consumed raw milk in Minnesota during the 10-year study period may have acquired an illness caused by 1 of these enteric pathogens.

"The results indicate that the number of sporadic raw milk–associated illnesses is likely substantial, greatly exceeding the number of cases linked to recognized raw milk–associated outbreaks," the authors write. "[T]he number of cases associated with reported raw milk consumption appears to be increasing, just as the movement to relax regulation of raw milk sales appears to be gaining momentum in many states."

The researchers found that hemolytic uremic syndrome occurred among 21% of the patients infected with STEC O157 who required hospitalization, including 2 of 4 children younger than 3 years. An 11-month-old infant with this infection died. In addition, hemolytic uremic syndrome occurred in 1 of the 12 patients with non-O157 STEC infection who required hospitalization.

Minnesota is among the 30 states in the United States that allows the sale of raw milk, and the majority (71%) of case-patients reported obtaining the raw milk either from their own dairy farm or from the farm of a relative. Other sources included nonrelative farmers (13%), the workplace (10%), drop-off sites (2%), and other sources including at daycare or school (3%).

The authors note limitations to the study such as the sporadic nature of the cases and the potential for overestimating illness caused by raw milk consumption. Conversely, patients who refused to answer questions about raw milk consumption were excluded from the study, which may have led to an underestimation of illnesses associated with raw milk consumption.

"During the study period, the number of patients with sporadic laboratory-confirmed infections who reported raw milk consumption (n = 530) was 25 times greater than the number of raw milk–associated outbreak cases (n = 21) among Minnesota residents," write the study authors. "Findings such as ours should be used to further educate potential raw milk consumers, as well as policy makers who might be asked by constituents to relax regulations regarding raw milk sales."

This work was supported in part through cooperative agreements with the Centers for Disease Control and Prevention.

Emerg Infect Dis. Published online December 11, 2013.

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