Investigation of Multidrug-Resistant Salmonella Serotype Typhimurium DT104 Infections Linked to Raw-Milk Cheese in Washington State
1999
ContextMultidrug-resistant Salmonella Typhimurium
DT104 has recently emerged as a cause of human and animal illness in
Europe and North America. In early 1997, health officials in Yakima
County, Washington, noted a 5-fold increase in salmonellosis among the
county's Hispanic population.ObjectivesTo characterize bacterial strains and identify risk
factors for infection with Salmonella Typhimurium in Yakima
County.DesignLaboratory, case-control, and environmental investigations.Setting and ParticipantsPatients with culture-confirmed
Salmonella Typhimurium infection living in Yakima County and
age- and neighborhood-matched control subjects.Main Outcome MeasuresFood vehicle implication based on
case-control study and outbreak control.ResultsBetween January 1 and May 5, 1997, 54
culture-confirmed cases of Salmonella Typhimurium were
reported. The median age of patients was 4 years and 91% were
Hispanic. Patients reported diarrhea (100%), abdominal cramps (93%),
fever (93%), bloody stools (72%), and vomiting (53%); 5 patients
(9%) were hospitalized. Twenty-two patients and 61 control subjects
were enrolled in the case-control study. Seventeen case patients (77%)
reported eating unpasteurized Mexican-style soft cheese in the 7 days
before onset of illness compared with 17 control subjects (28%)
(matched odds ratio, 32.3; 95% confidence interval, 3.0-874.6). All
case-patient isolates were phage definitive type 104 (DT104)
(n=10) or DT104b (n=12), and 20 (91%)
were resistant to ampicillin, chloramphenicol, streptomycin,
sulfamethoxazole, and tetracycline. The cheese produced and eaten by 2
unrelated patients was made with raw milk traced to the same local
farm. Milk samples from nearby dairies yielded Salmonella
Typhimurium DT104. The incidence of Salmonella Typhimurium
infections in Yakima County returned to pre-1992 levels following
interventions based on these findings.ConclusionsMultidrug-resistant Salmonella Typhimurium
DT104 emerged as a cause of salmonellosis in Yakima County, and
Mexican-style soft cheese made with unpasteurized milk is an important
vehicle for Salmonella Typhimurium DT104 transmission. We
postulate that recent increases in human salmonellosis reflect the
emergence of Salmonella Typhimurium DT104 among dairy cows in
the region. Continued efforts are needed to discourage consumption of
raw milk products, promote healthier alternatives, and study the
ecology of multidrug-resistant Salmonella
Typhimurium.
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