Date of Award

January 2025

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

James Hadler

Second Advisor

Robert Heimer

Abstract

Background: Shiga toxin-producing Escherichia coli (STEC) causes over 265,000 infections, 3,600 hospitalizations, and 30 deaths annually in the U.S.. While STEC O157 is the most common serotype, the increased use of culture-independent diagnostic tests (CIDT) led to a rise in non-O157 serotypes detected. Nationally, STEC incidence declined during the COVID-19 pandemic but has since surpassed pre-pandemic levels. An analysis was conducted to determine the changes that occurred in STEC infections in Connecticut from pre-pandemic to post-pandemic and to identify differences between culture-confirmed cases and CIDT-only/untyped cases.Methods: A descriptive analysis using STEC surveillance data collected in Connecticut was performed to identify changes in STEC infections, comparing cases reported in 2018–2019 (N = 238) to 2023–2024 (N = 342) by demographic characteristics, testing method, and exposure history. A case-case analysis was conducted among post-pandemic infections to identify differences between serotyped/culture-confirmed cases (N = 126) and CIDT-only/untyped cases (N = 216). Results: The overall incidence of STEC infections increased post-pandemic (RR 1.44, 95% CI 1.22-1.70). Incidence in the Hispanics/Latinos doubled (RR 1.98, 95% CI 1.40-2.79), driven by adults 18-64 years of age, to a rate that was nearly double that of any race/ethnic group. The proportion of culture-confirmed infections halved from pre-pandemic to post-pandemic (OR 0.49, 95% CI 0.35-0.63). Among confirmed infections, O157 decreased (26.9% pre-pandemic to 15.1% post-pandemic) while non-O157 increased (71.5% pre-pandemic to 80.2% post-pandemic). Farm animal exposure increased (OR 4.15, 95% CI 1.20-14.34). CIDT-only infections compared to culture-confirmed infections were 27.0% as likely to have bloody diarrhea (27.0% vs 51.3%) but were just as likely to have HUS and to be hospitalized. CIDT-only cases were also more likely (p<0.05) to be ≥65 years old (29.6% vs 14.3%), less likely to have attended or worked at a daycare (3.3% vs 12.1%), and be outbreak-associated (0% vs 17.5%). Conclusions: STEC incidence increased post-pandemic, driven by a rise in non-O157 serotypes and greater use of CIDT methods, with the most substantial increases among Hispanic/Latino adults and older populations. Changes in incidence highlight the need for continued surveillance.

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