Investigation of multidrug-resistant Salmonella serotype Typhimurium DT104infections linked to raw-milk cheese in Washington State

Context Multidrug-resistant Salmonella Typhimurium DT104 has recently emerg ed as a cause of human and animal illness in Europe and North America. In e arly 1997, health officials in Yakima County, Washington, noted a 5-fold in crease in salmonellosis among the county's Hispanic population. Objectives To characterize bacterial strains and identify risk factors for infection with Salmonella Typhimurium in Yakima County. Design Laboratory, case-control, and environmental investigations. Setting and Participants Patients with culture-confirmed Salmonella Typhimu rium infection living in Yakima County and age- and neighborhood-matched co ntrol subjects. Main Outcome Measures Food vehicle implication based on case-control study and outbreak control. Results Between January 1 and May 5, 1997, 54 culture-confirmed cases of Sa lmonella 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 enrol led in the case-control study. Seventeen case patients (77%) reported eatin g unpasteurized Mexican-style soft cheese in the 7 days before onset of ill ness compared with 17 control subjects (28%) (matched odds ratio, 32.3; 95% confidence interval, 3.0-874.6). All case-patient isolates were phage defi nitive type 104 (DT104) (n = 10) or DT104b (n = 12), and 20 (91%) were resi stant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and t etracycline. The cheese produced and eaten by 2 unrelated patients was made with raw milk traced to the same local farm. Milk samples from nearby dair ies yielded Salmonella Typhimurium DT104. The incidence of Salmonella Typhi murium infections in Yakima County returned to pre-1992 levels following in terventions based on these findings. Conclusions Multidrug-resistant Salmonella Typhimurium DT104 emerged as a c ause 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 salmonellos is reflect the emergence of Salmonella Typhimurium DT104 among dairy cows i n the region. Continued efforts are needed to discourage consumption of raw milk products, promote healthier alternatives, and study the ecology of mu ltidrug-resistant Salmonella Typhimurium.