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Gastrointestinal Infections

Multistate Salmonella outbreak linked to unpasteurized milk

Some consumers believe that raw milk is better than pasteurized milk.

August 2003

ATLANTA — Consumption of raw milk and milk products is believed to be

the source of a large multistate outbreak of Salmonella typhimurium

in 2002, according to researchers from the CDC.

In 2002, intrastate sale of raw milk for human consumption was legal

in 28 states, including Ohio, where the initial reports of Salmonella

were seen in two hospitalized children infected with Salmonella

enterica serotype typhimurium.

CDC officials reported in the Morbidity and Mortality Weekly Report

that the dairy involved in the outbreak was the only place in Ohio

selling raw milk legally. However, after the Salmonella was detected,

the Ohio Department of Agriculture revised its guidelines about the

sale of raw milk, and the dairy voluntarily relinquished its license

for selling raw milk.

Between Nov. 30, 2002 and Feb. 18, 2003, the Ohio Department of

Health laboratory received 94 S. typhimurium clinical isolates for

pulsed-field gel electrophoresis (PFGE) testing. Of these, 60 had an

indistinguishable pattern.

In 2002, intrastate sale of raw milk for human consumption was

legal in 28 states, including Ohio, where the initial reports of

Salmonella were seen.

The researchers found 62 people with infection, including 40

customers, six household contacts and 16 (7.6%) of 211 dairy workers.

All patients were from four states. The most common symptoms

associated with illness were diarrhea, cramps, fever, chills, body

aches, nausea and vomiting.

A case-control study was conducted to verify the initial findings

implicating raw milk and to identify other potential sources of

infection. The 40 case-patients who were dairy customers were

included in the study. There were 56 controls.

Of the 32 food samples tested, five were positive for S. typhimurium,

including three raw skim milk samples, one sample of butter made from

raw milk and one sample of cream. The PFGE pattern for all five food

isolates matched the outbreak pattern. The investigation showed that

four barn workers had asymptomatic S. typhimurium infection.

The researchers wrote that molecular subtyping of S. typhimurium

isolates had an important role in identifying cases that were part of

this outbreak and defining its extent. " Typhimurium is one of the

most common Salmonella serotypes isolated from persons in Ohio, and

without the specificity of PFGE typing, identifying cases that were

part of the outbreak would have been difficult, " researchers noted.

Despite the known association of raw milk with disease-causing

organisms, some consumers believe that raw milk is better than

pasteurized milk. The researchers wrote that consumer education about

the hazards of raw milk consumption would help. In addition, they

wrote, " retail milk regulations should be reviewed and strengthened,

if needed, to minimize exposure of the public to the hazards of raw

milk consumption. "

For more information:

CDC. Multistate outbreak of Salmonella serotype typhimurium

infections associated with drinking unpasteurized milk – Illinois,

Indiana, Ohio and Tennessee, 2002-2003. MMWR. 2003;52(26): 613-615.