Prevalence of Salmonella and multiple antimicrobial-resistant Salmonella in California dairies.

A cross-sectional survey was conducted on 75 randomly selected dairies in one California county. Salmonella was isolated from 12 (16%) dairies; S newport was isolated from 6 (8%). Chloramphenicol-resistant S newport and S dublin were isolated from 8 (10.7%) dairies. Dairies with Salmonella had higher average calf mortality rates (P = 0.064; odds ratio [OR], 3.8). Dairies with S newport had a greater than expected occurrence of illnesses in adult cows compared with dairies with no S newport (P = 0.048; OR, 6.7) or with no Salmonella serotypes isolated (P = 0.047; OR, 6.9). Dairies with chloramphenicol-resistant Salmonella were more likely to have used chloramphenicol during the preceding 18-month period compared with dairies with chloramphenicol-susceptible Salmonella or no Salmonella (P = 0.023; OR, 9.5).