Relationship between in vitro sensitivity of coliform pathogens in the udder and the outcome of treatment for clinical mastitis

The relationship between in vitro sensitivity to antimicrobials and the outcome of treatment was studied in 228 cows with coliform mastitis. All the cows were treated with a preparation containing sulphonamide and trimethoprim, and 197 of them were also treated with a non-steroidal anti-inflammatory drug (NSAID). The relationship between in vitro sensitivity to sulphonamide/trimethoprim and recovery was analysed by multivariate logistic regression. The possible confounding effects of treatment with an NSAID, days in lactation, parity, herd, and type of infecting organism were tested. Only treatment with an NSAID had a significant confounding effect and was included in the final statistical model. The recovery rate of the 165 cows infected by coliforms that were sensitive to sulphonamide/trimethoprim (89·1 per cent) was higher than that of the 63 cows infected by coliforms that were resistant to sulphonamide/trimethoprim (74·6 per cent). The odds ratio of recovery for the cases associated with organisms that were sensitive to sulphonamide/trimethoprim relative to the cases associated with organisms that were resistant to sulphonamide/trimethoprim was 2·75, with a 95 per cent confidence from 1·25 to 5·85. The odds ratio of recovery for the cases treated with an NSAID relative to the cases treated with sulphonamide/trimethoprim only was 2·76 with a 95 per cent confidence interval from 1·12 to 6·79.