Health Outcomes from Multi-Drug-resistant Salmonella Infections in High-Income Countries: A Systematic Review and Meta-Analysis

BACKGROUND Salmonella is a leading cause of foodborne enterocolitis worldwide. Antimicrobial use in food animals is the driving force for antimicrobial resistance among Salmonella particularly in high-income countries. Nontyphoidal Salmonella (NTS) infections that are multidrug resistant (MDR) (nonsusceptible to ≥1 agent in ≥3 antimicrobial categories) may result in more severe health outcomes, although these effects have not been systematically examined. We conducted a systematic review and meta-analysis to examine impacts of MDR NTS on disease outcomes in high-income settings. METHODS We systematically reviewed the literature from scientific databases, including PubMed, Scopus, and grey literature sources, using preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. We included peer-reviewed publications of case-control and cohort studies, outbreak investigations, and published theses, imposing no language restriction. We included publications from January 1, 1990 through September 15, 2016 from high-income countries as classified by the World Bank, and extracted data on duration of illness, hospitalization, morbidity and mortality of MDR, and pan-susceptible NTS infections. RESULTS After removing duplicates, the initial search revealed 4258 articles. After further screening, 16 eligible studies were identified for the systematic review, but, only 9 of these were included in the meta-analysis. NTS serotypes differed among the reported studies, but serotypes Typhimurium, Enteritidis, Newport, and Heidelberg were the most often reported MDR pathogens. Salmonella infections that were MDR were associated with excess bloodstream infections (odds ratio [OR] 1.73; 95% confidence interval [CI] 1.32-2.27), more frequent hospitalizations (OR 2.51; 95% CI 1.38-4.58), and higher mortality (OR 3.54; 95% CI 1.10-11.40) when compared with pan-susceptible isolates. CONCLUSIONS Our study suggests that MDR NTS infections have more serious health outcomes compared with pan-susceptible strains. With the emergence of MDR Salmonella strains in high-income countries, it is crucial to reduce the use of antimicrobials in animals and humans, and intervene to prevent foodborne infections.