Traditional Salmonella Typhimurium typing tools (phage typing and MLVA) are sufficient to resolve well-defined outbreak events only.

Between 1991 and 2014 the per capita notification rate of salmonellosis in Australia increased from 31.9 to 69.7 cases per 100,000 people. Salmonella Typhimurium accounted for nearly half the human cases until the end of 2014. In this study, we used cluster analysis tools to compare S. Typhimurium isolates from a chicken-meat study with those reported to the National Enteric Pathogen Surveillance System (NEPSS) from the coincident human and non-human populations. There was limited phage type diversity within all populations and a lack of specificity of MLVA profiling within phage types. The chicken-meat study isolates were not significantly clustered with the human cases and at least 7 non-human sources, based on typing profiles (PT/MLVA combination), could be implicated as a source of human cases during the same period. In the absence of a strong surveillance system representative of all putative sources, MLVA and phage typing alone or in combination are insufficient to identify the source of human cases.

Does only the age of the hen matter in Salmonella enterica contamination of eggs?

Contamination of eggs with Salmonella enterica is a significant risk factor contributing to foodborne disease. Periods of peak egg contamination were identified by conducting longitudinal environmental and egg sampling in 7 layer flocks until they were 50 weeks of age. A total of 714 environmental samples and 8958 eggs were cultured using standard methods for the detection of salmonellae. Pooled egg contamination with Salmonella Typhimurium or Salmonella Infantis was detected at a true prevalence (TP) of 0.002 (95% CI = 0.001, 0.004) or 0.005 (95% CI = 0.004, 0.007), respectively. S. Typhimurium and S. Infantis were detected in individual egg components; in shell rinse at a TP of 0.014 (95% CI = 0.005, 0.038), in shell and membrane at a TP of 0.01 (95% CI = 0.003, 0.032), and in albumen and yolk content at a TP of 0.007 (95% CI = 0.001, 0.027). The concentration of salmonellae in all fractions was <1 CFU/mL. The TP of Salmonella enterica in eggs was highest at the onset of lay. Higher egg prevalence was associated with a lower body weight, higher egg production, higher egg weight and mass than the breed standard for age, and poorer feed conversion efficiency. Flock physiology appears to have an important influence on the detection of eggs contaminated with Salmonella enterica.

Salmonella spp. transmission in a vertically integrated poultry operation: Clustering and diversity analysis using phenotyping (serotyping, phage typing) and genotyping (MLVA).

The transmission of Salmonella enterica within a vertically integrated poultry operation was investigated longitudinally over an 18-month period (2013-2014). Thirty six percent of all samples collected (1503 of 4219) were positive for salmonellae with seven Salmonella enterica subsp. enterica serovars, and one Salmonella enterica subsp. salamae serovar detected. Both Salmonella enterica subsp. enterica serovars Infantis and Typhimurium were detected in all locations sampled. Salmonella Typhimurium was the most frequently detected serovar (63% of serotyped samples) with 8 phage types (PT) and 41 multiple-locus variable-number tandem-repeats analysis (MLVA) profiles identified. The most frequently identified phage types were PT135a and DT135. A total of 62 PT/MLVA combinations were observed. MLVA profiles 03-14-10-09-525 and 03-15-11-11-525 were the most frequently identified and 83% of the isolates shared at least one MLVA profile with an isolate from another phage type. The use of phage typing and MLVA profiling, on their own or in combination, were insufficient to understand the complexity of the epidemiological relationships between locations within this production system. Despite the high level of apparent diversity, cluster analysis was unable to differentiate the transmission pathways of all S. Typhimurium variants detected within the integrated enterprise. Using additional epidemiological information, the parent breeder rearing site was identified as the most likely point of introduction of two S. Typhimurium isolates into the production system with subsequent dissemination to the broiler flocks via the hatchery. This complexity is unable to be resolved in the absence of intensive sampling programs at all generations of the production system.

The use of social network analysis to examine the transmission of Salmonella spp. within a vertically integrated broiler enterprise.

To better understand factors influencing infectious agent dispersal within a livestock population information is needed on the nature and frequency of contacts between farm enterprises. This study uses social network analysis to describe the contact network within a vertically integrated broiler poultry enterprise to identify the potential horizontal and vertical transmission pathways for Salmonella spp. Nodes (farms, sheds, production facilities) were identified and the daily movement of commodities (eggs, birds, feed, litter) and people between nodes were extracted from routinely kept farm records. Three time periods were examined in detail, 1- and 8- and 17-weeks of the production cycle and contact networks were described for all movements, and by commodity and production type. All nodes were linked by at least one movement during the study period but network density was low indicating that all potential pathways between nodes did not exist. Salmonella spp. transmission via vertical or horizontal pathways can only occur along directed pathways when those pathways are present. Only two locations (breeder or feed nodes) were identified where the transmission of a single Salmonella spp. clone could theoretically percolate through the network to the broiler or processing nodes. Only the feed transmission pathway directly connected all parts of the network.