Salmonella Outbreaks in Low- and Middle-Income Countries over the Last Decade: A Systematic Review and Meta-Analysis of Transmission Dynamics, Clinical Outcomes, and Antimicrobial Resistance.

Abstract

Background: Salmonella outbreaks persist as a public health burden in low- and middle-income countries (LMICs), yet comprehensive synthesis of their epidemiology over the past decade remains limited.

Methods: Following PRISMA 2020 guidelines, we searched PubMed, Scopus, Web of Science, and Google Scholar for laboratory-confirmed Salmonella outbreaks in LMICs (1 January 2016-1 January 2026). Random-effects meta-analysis estimated pooled prevalence rates, with statistical heterogeneity quantified using I² statistic. Given extreme heterogeneity across most outcomes (I² > 90%), we present individual study ranges alongside pooled estimates.

Results: Twenty-four studies from 14 LMICs met inclusion criteria. Salmonella Typhi was the predominant pathogen (70.8% of outbreaks). Waterborne transmission was most frequent (37.5%), predominating in Africa (83.3%), whereas foodborne and fecal-oral routes were common in Asia. Pooled laboratory confirmation rate was 28.02% (95% CI: 12.2-52.1; observed range: 1.5-100%), varying by region: Southeast Asia 54.2% (95% CI: 4.3-96.9), Western Pacific 27.6% (95% CI: 8.0-56.9), and Africa 6.1% (95% CI: 5.3-6.9). The pooled case fatality rate was 7.0% (95% CI: 3.4-13.7; range: 3.6-10.0%). Fever (93.0%), abdominal pain (53.6%), and headache (52.0%) were most common symptoms. Pooled antimicrobial resistance reached 59.3% (95% CI: 26.6-85.4%), highest for trimethoprim-sulfamethoxazole (94.2%) and ciprofloxacin (61.3%). Extreme heterogeneity and wide confidence intervals were observed across some pooled estimates and should be interpreted with caution.

Conclusions: Salmonella outbreaks in LMICs are characterized by high S. Typhi prevalence and predominant waterborne transmission. Elevated mortality and widespread first-line antibiotic resistance show the need for improved WASH infrastructure, enhanced real-time outbreak surveillance, and revised empiric treatment protocols.