Characteristics of the epidemic process of Salmonella infection among the residents of Saint Petersburg

Introduction: The incidence of salmonellosis in St. Petersburg remains at one of the highest levels in the Russian Federation.

Objective: To establish features of the epidemic process of Salmonella infection among the residents of St. Petersburg, including those in outpatients.

Materials and methods: The study was conducted in the years 2020 to 2023 and consisted of a retrospective epidemiological analysis of data retrieved from the register of infectious and parasitic diseases kept by the Center for Hygiene and Epidemiology in the city of St. Petersburg and the Leningrad Region for 2017–2021 and from medical records of cases receiving outpatient care at a health center of St. Peterburg in 2018–2019. Risk factors were established in a case-control study with 120 cases and 142 controls. We calculated the odds ratio (OR), confidence intervals, significance level (p), and Chi-square for each risk factor.

Results: Our findings showed that the long-term incidence rate of salmonellosis in 2017–2021 was 31.9 ± 3 per 100,000 population, with most cases (87.5 %) induced by S. Enteriditis and 65 % of the confirmed cases hospitalized. The risk group included children under 7 years of age. The incidence in children not attending preschools/schools (198.0; 95 % CI: 175.1–223.9) was higher than in their organized peers (122.2; 95 % CI: 108.5–136.1). The seasonal rise in the former and adults started in summer and ended in November, while in the latter it was noted only in August and September. Results of the case-control study demonstrated that eating in school canteens and catering facilities reduced the risk of Salmonella infection (OR = 0.57; 95 % CI: 0.36–0.90; p = 0.016 and OR = 0.52; 95 % CI: 0.32–0.86; p = 0.016, respectively). Contacts with amphibians and/or reptiles (OR = 6.85; 95 % CI: 0.81–57.6; p = 0.041) and acute intestinal infection symptoms in family members (OR = 51.0; 95 % CI: 6.88–378; p = 0.001) were found to be the risk factors for salmonellosis.

Conclusion: High incidence of salmonellosis in St. Petersburg with the majority of sporadic cases requires improvement of the epidemiological surveillance system.

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