Abstract
Salmonella is one of the most important foodborne pathogens worldwide. Its main reservoirs are poultry and pigs, in which infection is endemic in many countries. Spain has one of the largest pig populations in the world. Even though Salmonella infection is commonly detected in pig farms, its spatial distribution at the national level is poorly understood. Here we aimed to report the spatial distribution of Salmonella-positive pig farms in Spain and investigate the presence of potential spatial trends over a 17-year period. For this, data on samples from pigs tested for Salmonella in 2002–2013, 2015, 2017, and 2019 as part of the Spanish Veterinary Antimicrobial Resistance Surveillance program, representing 3,730 farms were analyzed. The spatial distribution and clustering of Salmonella-positive pig farms at the province level were explored using spatial empirical Bayesian smoothing and global Moran's I, local Moran's I, and the Poisson model of the spatial scan statistics. Bayesian spatial regression using a reparameterized Besag-York-Mollié Poisson model (BYM2 model) was then performed to quantify the presence of spatially structured and unstructured effects while accounting for the effect of potential risk factors for Salmonella infection at the province level. The overall proportion of Salmonella-positive farms was 37.8% (95% confidence interval: 36.2–39.4). Clusters of positive farms were detected in the East and Northeast of Spain. The Bayesian spatial regression revealed a West-to-East increase in the risk of Salmonella infection at the province level, with 65.2% (50% highest density interval: 70–100.0%) of this spatial pattern being explained by the spatially structured component. Our results demonstrate the existence of a spatial variation in the risk of Salmonella infection in pig farms at the province level in Spain. This information can help to optimize risk-based Salmonella surveillance programs in Spain, although further research to identify farm-level factors explaining this pattern are needed.
Highlights
Salmonella infection is one of the most important foodborne zoonoses worldwide
The current study shows a notable increasing trend in the risks of Salmonella infection in pig farms located in provinces from West to East in Spain, evident still after the possible effect of the heterogeneous distribution of pigs in the country was accounted for
The increase in the percentage of Salmonella positive farms from 2012 and the S. 1,4,[5],12:i:- in Spain demonstrates the usefulness of surveillance to detect changes in the epidemiology of this foodborne pathogen in the animal reservoirs
Summary
Salmonella infection is one of the most important foodborne zoonoses worldwide. There were 91,662 confirmed human salmonellosis cases in 2017 in the European Union (EU) [1] and ∼1.2 million estimated cases occur every year in the US [2]. Salmonellosis, characterized by acute onset of fever, abdominal pain, diarrhea, and nausea, is usually self-limiting. Sometimes it can be life-threatening, especially in children, elderly and immunosuppressed patients, requiring antimicrobial therapy [3]. Typhimurium and its monophasic variant (1,4,[5],12:i:-), were among the top serotypes associated with human salmonellosis in Spain [1]. The European Food Safety Authority (EFSA) baseline reports on Salmonella infection in fattening and breeder pig farms in Europe demonstrated that Spain had one of the highest levels of infection in pigs among EU countries, further highlighting their potential role in the occurrence of human salmonellosis in Spain [8, 9]
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