Prevalence and molecular characterization of Salmonella spp. from clinical, food, and environmental sources in Addis Ababa and surrounding towns, Ethiopia.

INTRODUCTION

Salmonella spp. are a major cause of foodborne diarrheal disease, particularly in low- and middle-income countries. Poor sanitation and unsafe food handling facilitate the transmission and persistence of Salmonella in human, animal, and environmental sources. This study focused on assessing the prevalence of Salmonella spp. obtained from stool, food, and environmental samples in Addis Ababa and its surrounding towns.

METHODS

A total of 552 samples were collected, comprising 386 stool samples from diarrheic outpatients along with full demographic data and 166 food and environmental samples, including meat (n = 57) and sewage from slaughterhouses (n = 16), chicken intestines (n = 42), and chicken droppings (n = 51). Stool samples were transported in Cary-Blair transport media while food and environmental samples were collected in buffered peptone water. Samples were enriched in selenite broth and cultured on MacConkey and Xylose Lysine Deoxycholate (XLD) agar, and differentiated as lactose fermenting and non-lactose fermenting. Biochemical tests, including Triple Sugar Iron (TSI), Urea, Citrate, and Lysine Iron Agar (LIA), were performed for presumptive identification of the isolates, which were further confirmed using polyvalent Salmonella antisera. All biochemically identified isolates were further subjected to PCR test targeting invA gene and serovar-specific markers.

RESULTS

Behavioral analysis indicated that 26.8% of patients reported consumption of raw or undercooked food prior to illness, and a significant association was observed between Salmonella infection and raw food consumption (p < 0.001). Among the 386 stool samples analyzed, 8.56% (33/386) tested positive for Salmonella by PCR. Among food and environmental sources, the highest prevalence was observed in chicken intestinal samples (28.57%, 12/42), followed by meat samples, specifically cattle lymph nodes (21.88%, 7/31), chicken droppings (7.69%, 4/52), surface swabs (7.41%, 2/26), and wastewater samples (6.25%, 1/16). Generally, Salmonella was confirmed in 61 of 552 samples (11.05%) using PCR targeting the conserved invA gene. Screening revealed source-specific detection patterns, with higher positivity in animal intestinal samples compared with environmental sources, highlighting potential reservoirs of Salmonella within a One Health framework.

CONCLUSION

Salmonella spp. pose a significant public health threat across interconnected human, animal, and environmental settings in Addis Ababa and surrounding areas. Strengthening sanitation, improving food safety practices along the animal-to-human food chain, and enhancing integrated surveillance are essential to reduce transmission and mitigate the burden of salmonellosis within a One Health framework.