Risk factor analysis for Salmonella contamination of broiler chicken (Gallus gallus) hatcheries in Great Britain.

Salmonellosis is the second most commonly reported zoonosis in the European Union and contaminated meat from broiler chickens (Gallus gallus) is an important source of human infection. In Great Britain (GB), prevalence of Salmonella enterica in broiler flocks is low, having declined considerably since the introduction of the Salmonella National Control Programme in 2010. However, this decreasing trend has stabilised in recent years and serovars with known ability to persistently colonise hatcheries have been isolated from broiler flocks with increasing frequency, indicating that further controls on hatchery contamination are required. The broiler industry in GB has changed dramatically over the last 15 years, with greater intensification and dominance by a small number of very large companies which rely on relatively few hatcheries. An investigation of risk factors for Salmonella contamination in GB broiler hatcheries was therefore carried out so that relevant up-to-date advice on Salmonella control can be provided. Twenty-two hatcheries, representing most commercial scale GB broiler hatcheries, were visited between 2015 and 2018. Salmonella contamination was comprehensively investigated at each hatchery by collecting between 108 and 421 environmental swab samples per hatchery (6990 samples in total from all hatcheries). An in-depth questionnaire on hatchery operations was completed for each hatchery, and results were incorporated into a risk factor analysis (univariable followed by multivariable mixed effects logistic regression) to identify factors associated with Salmonella occurrence. Overall, 6.0 % (416/6990) of environmental samples were Salmonella-positive and Salmonella was isolated from 17/22 hatcheries. Ten different serovars were isolated, the most common being S. Senftenberg and S. Mbandaka which are known hatchery colonisers. Sixty-four risk factor variables were investigated. Twenty-two of these were initially retained based on univariable analyses (p ≤ 0.25) and six were ultimately left in the final multivariable model (p ≤ 0.05). Salmonella detection was positively associated with having ≥30 hatchers in regular use compared to fewer (Odds ratio [OR] 23.7, 95 % confidence interval [CI] 6.7-84.2), storing trays in process rooms (OR 28.8, CI 7.8-106.3), drying set-up trolleys in corridors (OR 15.6, CI 5.9-41.4) and having skips located in enclosed areas (OR 8.99, CI 5.89-41.35). Using a closed waste disposal system was negatively associated with Salmonella detection (OR 0.08, CI 0.04-0.18) and the odds of detecting Salmonella in hatcheries with 31-60 total workers was lower compared to hatcheries with ≤30 staff (OR 0.16, CI 0.06-0.40). Despite the complexities of hatchery enterprises, changes to a relatively small number of features may significantly reduce the occurrence of hatchery contamination.

Field investigations of multidrug-resistant Salmonella Infantis epidemic strain incursions into broiler flocks in England and Wales.

Salmonella Infantis is a major public health concern and has become established in the broiler sector in some European countries, as well as globally, and is frequently multidrug resistant (MDR). Three broiler farms in England and Wales, which had incursions of MDR S. Infantis between 2013 and 2017, were investigated longitudinally. The company feed mill and two associated hatcheries were intensively sampled. Following each visit, advice on cleaning, disinfection and other control measures for Salmonella was given to help eliminate S. Infantis from the premises. Four samples collected from inside the broiler houses after cleaning and disinfection were Salmonella-positive, indicating cleaning and disinfection within houses was generally effective. However, the exterior of persistently infected houses remained substantially contaminated and feeding systems could not be sampled. Clearance of S. Infantis from affected houses requires additional attention to decontamination of these aspects. Sixty S. Infantis isolates were tested for antimicrobial susceptibility by disk diffusion tests. All isolates were MDR, with resistance to at least nalidixic acid (Na), tetracycline (T), compound sulphonamide (Su), streptomycin (S) and furazolidone. This is a similar resistance pattern to the previously identified MDR (NaSSuT) clone in some European countries. The study shows that to remove S. Infantis from premises effectively, a combined approach to poultry houses and the surrounding farm environment is necessary. A revised cleaning and disinfection programme was developed that was associated with the clearance of MDR S. Infantis from persistently infected and newly infected broiler flocks, and UK livestock remains free of MDR S. Infantis. RESEARCH HIGHLIGHTS Standard cleaning and disinfection protocols did not completely eliminate infection. A revised cleaning and disinfection programme was developed. Disinfecting feeder lines and external areas was key to eliminating S. Infantis. Identified similar antimicrobial resistance pattern to MDR epidemic S. Infantis.