Prevalence and risk factors associated with Campylobacter spp. and Salmonella enterica in livestock raised on diversified small-scale farms in California.

Diversified farms are operations that raise a variety of crops and/or multiple species of livestock, with the goal of utilising the products of one for the growth of the other, thus fostering a sustainable cycle. This type of farming reflects consumers' increasing demand for sustainably produced, naturally raised or pasture-raised animal products that are commonly produced on diversified farms. The specific objectives of this study were to characterise diversified small-scale farms (DSSF) in California, estimate the prevalence of Salmonella enterica and Campylobacter spp. in livestock and poultry, and evaluate the association between farm- and sample-level risk factors and the prevalence of Campylobacter spp. on DSSF in California using a multilevel logistic model. Most participating farms were organic and raised more than one animal species. Overall Salmonella prevalence was 1.19% (95% confidence interval (CI95) 0.6-2), and overall Campylobacter spp. prevalence was 10.8% (CI95 = 9-12.9). Significant risk factors associated with Campylobacter spp. were farm size (odds ratio (OR)10-50 acres: less than 10 acres = 6, CI95 = 2.11-29.8), ownership of swine (OR = 9.3, CI95 = 3.4-38.8) and season (ORSpring: Coastal summer = 3.5, CI95 = 1.1-10.9; ORWinter: Coastal summer = 3.23, CI95 = 1.4-7.4). As the number of DSSF continues to grow, evaluating risk factors and management practices that are unique to these operations will help identify risk mitigation strategies and develop outreach materials to improve the food safety of animal and vegetable products produced on DSSF.

Risk factors associated with persistence of Salmonella shedding in finishing pigs.

The objective of this study was to identify risk factors associated with persistence of Salmonella shedding in finishing swine. A longitudinal study was conducted in 18 cohorts of pigs from three finishing sites of one swine production company. Among the 446 Salmonella isolates (isolated from 187 pigs), there were 18 distinct serovars. The six most common serovars were S. enterica serovar Derby (47.3%), S. Agona (27.4%), S. Johannesburg (10.5%), S. Schwarzengrund (2.7%), S. Litchfield (2.5%) and S. Mbandaka (2.2%). Survival analysis techniques, Kaplan-Meier methods and Log-rank test were used to estimate the duration of Salmonella shedding in days and to evaluate differences in shedding associated with risk factors at different organizational levels: isolate (serovar), pig, cohort and site. The risk factors at the pig-level were: sex, age and individual health status; and the risk factors at the cohort-level were: health risk, treatment and "at risk pigs" proportions, nursery and barn environment Salmonella status and prior exposure to the same serovar in the nursery or barn environment. Survival analysis using acceleration failure time models, with a log-normal distribution, was applied to investigate risk factors associated with Salmonella persistence (175 pigs) and serovar-specific persistence (151 pigs) during the study period. Pigs detected Salmonella positive for the first time at 10 weeks of age had a longer duration of shedding, than pigs first detected at an older age. The duration of shedding was shorter among pigs infected with S. Derby, S. Johannesburg and other serovars as compared to pigs infected with S. Agona. A significant difference was observed among sites. Cohorts with pig treatment proportions greater than the median were more likely to have a shorter duration of Salmonella shedding. Pigs from cohorts with nursery positive pools greater than the overall mean had a longer duration of Salmonella shedding as compared to pigs from cohorts with nursery pools less than or equal to the mean. These results suggest that the duration of Salmonella shedding may depend on Salmonella serovar, pig age at the time of infection, farm site and cohort-level risk factors. Identification of risk factors associated with the duration of shedding may allow more targeted interventions for the control Salmonella by evaluation of control measures not only for prevalence reduction, but also to decrease the duration of shedding. Such measures may decrease the risk of contamination of pork and subsequent risk of foodborne illness.

Longitudinal study to evaluate the association between thermal environment and Salmonella shedding in a midwestern US swine farm.

The objective of this study was to document the association between the thermal environment in the barn and Salmonella shedding in finishing pigs. For this purpose, individual fecal samples from 900 finishing pigs (8 collections per pig) were repeatedly collected from 18 cohorts (50 pigs per cohort) on 3 sites of a multi-site farrow-to-finish production system in a longitudinal study. Pen temperature and humidity were measured every 2 min during the study period. The thermal parameters of interest were: hourly average temperature, minimum and maximum temperature, hourly temperature variation, temperature humidity index (THI) and cumulative number of hours/degree above and below the thermal neutral zone at the pen level prior to fecal sampling for 6 time periods (12h, 24h, 48 h, 72 h, 1 week and 1 month). Additional potential risk factors at the individual (e.g., sex, health events), cohort (e.g., mortality, morbidity, Salmonella status of the nursery) and pen level (e.g., type of pen) were also evaluated. Multilevel logistic models using generalized linear models, with random intercepts at pig, pen and cohort levels to account for clustering (individual samples nested within pigs, pigs nested within pens, pens within cohorts) were constructed. Site (A, B, C) was considered as a fixed effect in order to control for clustering within site. The outcome variable was Salmonella fecal status of the individual sample. Cold exposure (temperatures below the thermal neutral zone) and exposure to a THI>72 were both positively associated with risk Salmonella shedding. Nursery Salmonella status was positively associated with Salmonella shedding and pig age was negatively associated with Salmonella shedding. In the multilevel intercept-only model the largest proportion of model variance was associated with the individual fecal sample (44.8%) followed by cohort (24.5%), pen (20.5%) and pig (10.2%). The present study allowed the investigation of the association of time-variant thermal factors and Salmonella shedding. Interventions that target the thermal environment may have an effect on reducing Salmonella shedding in swine and also improve pig well-being and production efficiency. Alternatively, thermal parameters may be used to identify groups of pigs at high risk for Salmonella shedding. Future studies should be performed to investigate the cost-efficacy of interventions to improve the thermal environment of swine.

Longitudinal study of Salmonella shedding in naturally infected finishing pigs.

A 3-year longitudinal study was conducted on a multi-site farrow-to-finish production system. For each of 18 cohorts at three finishing sites, 50 pigs were randomly selected. Faecal samples were collected every 2 weeks for 16 weeks. Salmonella was cultured from 453 (6·6%) of 6836 faecal samples. The pig-level incidence of Salmonella was 20·8% (187/899 pigs). Salmonella prevalence varied between cohorts and within pigs. The adjusted Salmonella prevalence decreased over the finishing period from 6·4% to 0·8%. Intermittent detection of Salmonella was found in more than 50% of pigs that were positive at more than one collection. The finding that the majority of pigs shed intermittently has implications for surveillance and research study design when determining Salmonella status. The variability in shedding over time, as well as between and within cohorts and pigs suggests that there may be time-variant risk factors for Salmonella shedding in swine.