Risk Factors Associated with the Carriage of Pathogenic Escherichia coli in Healthy Commercial Meat Chickens in Queensland, Australia †

Abstract

Avian pathogenic E. coli (APEC) can cause avian colibacillosis, an economically important disease that contributes to bird mortality and the high costs associated with prevention and treatment. Little is known about APEC in the context of Australian conditions. The current study aimed to estimate the prevalence of APEC and determine the risk factors associated with cloacal carriage of APEC among commercial healthy meat chickens in Queensland. Cloacal swabs were collected at slaughter from 400 healthy meat chickens (ten per farm) originating from 40 farms. A total of 2200 E. coli isolates were selected from cultured swabs and screened for the presence of five APEC-associated virulence genes (VGs). Farm-level data were collected using a questionnaire. Binominal general linear models were used to identify farm-level risk factors associated with bird-level APEC prevalence. Thirty-four per cent of the cultured E. coli isolates (n = 751) were classified as APEC, with all farms testing positive for APEC, and the overall bird-level prevalence of APEC was 63.0%. Higher APEC within-farm bird-level prevalence was positively associated with the usage of well water as a source of drinking water (OR = 6.2, 95% CI: 2.3, 16.5, p < 0.001); not having shower facilities available for farm visitors (OR = 3.6, 95% CI: 1.8, 7.1, p < 0.001); distances greater than 20 m between the car park and the poultry shed (OR = 2.2, 95% CI: 1.4, 3.4, p = 0.001); not applying water line disinfection after each flock cycle (OR = 2.2, 95% CI: 1.4, 3.5, p = 0.001); the presence of wild birds within 50 m of the poultry shed (OR = 2.3, 95% CI: 1.4, 3.7, p = 0.001). Chlorine combined with automatic drinking water filtration reduced within-farm bird-level APEC prevalence (OR = 0.07, 95% CI: 0.02, 0.34, p = 0.001). This study identified a number of important factors associated with APEC and showed that improving biosecurity and water treatments might reduce the prevalence of APEC. The notable high APEC prevalence on all farms requires further epidemiological investigations.