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The importance of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) as an infectious agent for humans has increased in recent years in Germany. Although it is well known that the prevalence of MRSA in pig farms is high, risk factors for the presence of MRSA in herds of fattening pigs are still poorly understood. The aim of this study was to evaluate available data from previous studies on MRSA in fattening pigs in a meta-analysis to answer the question: What are the factors associated with the occurrence of MRSA in fattening pig herds?
The studies on MRSA in pigs that were identified by literature research were heterogeneous with respect to the risk factors investigated and the type of herds focused on. Therefore we decided to carry out a pooling analysis on herd level rather than a typical meta-analysis. Eligible herd data were identified based on the published literature and communication with the authors. The final data set covered 400 fattening pig herds from 10 different studies and 12 risk factors. The prevalence of MRSA in the 400 fattening pig herds was 53.5%.
Data were analyzed using generalized estimating equations (GEE). The resulting multi-variate model confirmed previously identified risk factors for MRSA in pig herds (herd size and herd type). It also identified further risk factors: group treatment of fattening pigs with antimicrobial drugs (OR=1.79) and housing fattening pig herds on at least partially slatted floors (OR=2.39) compared to plain floor. In contrast, according to the model, fattening pig herds on farms keeping other livestock along with pigs were less likely to harbor MRSA (OR=0.54).
The results underline the benefits from a pooling analysis and cooperative re-evaluation of published data. (C) 2014 The Authors. Published by Elsevier B.V.
Methicillin resistant Staphylococcus aureus (MRSA) is one of the most important antibiotic-resistant pathogens in hospitals and the community. Recently, a new generation of MRSA, the so called livestock associated (LA) MRSA, has emerged occupying food producing animals as a new niche. LA-MRSA can be regularly isolated from economically important live-stock species including corresponding meats. The present thesis takes a methodological approach to confirm the hypothesis that LA-MRSA are transmitted along the pork, poultry and beef production chain from animals at farm to meat on consumers` table. Therefore two new concepts were developed, adapted to differing data sets.
A mathematical model of the pig slaughter process was developed which simulates the change in MRSA carcass prevalence during slaughter with special emphasis on identifying critical process steps for MRSA transmission. Based on prevalences as sole input variables the model framework is able to estimate the average value range of both the MRSA elimination and contamination rate of each of the slaughter steps. These rates are then used to set up a Monte Carlo simulation of the slaughter process chain. The model concludes that regardless of the initial extent of MRSA contamination low outcome prevalences ranging between 0.15 and 1.15 % can be achieved among carcasses at the end of slaughter. Thus, the model demonstrates that the standard procedure of pig slaughtering in principle includes process steps with the capacity to limit MRSA cross contamination. Scalding and singeing were identified as critical process steps for a significant reduction of superficial MRSA contamination.
In the course of the German national monitoring program for zoonotic agents MRSA prevalence and typing data are regularly collected covering the key steps of different food production chains. A new statistical approach has been proposed for analyzing this cross sectional set of MRSA data with regard to show potential farm to fork transmission. For this purpose, chi squared statistics was combined with the calculation of the Czekanowski similarity index to compare the distributions of strain specific characteristics between the samples from farm, carcasses after slaughter and meat at retail. The method was implemented on the turkey and veal production chains and the consistently high degrees of similarity which have been revealed between all sample pairs indicate MRSA transmission along the chain.
As the proposed methods are not specific to process chains or pathogens they offer a broad field of application and extend the spectrum of methods for bacterial transmission assessment.