Multiresistant Salmonella Typhimurium DT104 infections of humans and domestic animals in the Pacific Northwest of the United States

Salmonella Typhimurium definitive type 104 with chromosomally encoded resis tance to five or more antimicrobial drugs (R-type ACSSuT+) has been reporte d increasingly frequently as the cause of human and animal salmonellosis si nce 1990, Among animal isolates from the northwestern United States (NWUS), R-type ACSSuT+ Typhimurium isolates increased through the early 1990s to c omprise 73 % of Typhimurium isolates by 1995, but subsequently decreased to comprise only 30 % of isolates during 1998. NWUS S. Typhimurium R-type ACS SuT+ were consistently (99 %) phage typed as DT104 or the closely related D Tu302, S. Typhimurium isolates from cattle with primary salmonellosis, rand omly selected from a national repository, from NWUS were more likely to exh ibit R-type ACSSuT+ (19/24, 79 %) compared to isolates from other quadrants (17/71, 24 %; P < 0.01). Human patients infected with R-type ACSSuT+ resid ed in postal zip code polygons of above average cattle farm density (P < 0. 05), while patients infected with other R-types showed no similar tendency. Furthermore, humans infected with R-type ACSSuT+ Typhimurium were more lik ely to report direct contact with livestock (P < 0.01) than humans infected with other R-types.