Temporal trends of Shigella outbreaks in the United States, 2009-2022

Shigella infections remain a significant public health threat in the United States because of their diverse outbreak patterns and high disease impact, particularly among young children. This study aimed to investigate the trends in Shigella outbreak incidence and demographic patterns by age and sex from 2009 to 2022 in order to inform targeted prevention strategies.

We performed a retrospective observational analysis of 1,208 Shigella outbreak surveillance data sourced from the Centers for Disease Control and Prevention (CDC) via the National Outbreak Reporting System (NORS). The incidence rates per 1 million population-years were calculated overall and by age and sex. Descriptive statistics were used to summarize the data, and joinpoint regression with 95% confidence intervals was used to identify trends.

The outbreak incidence rate was 0.27 (95% CI: 0.01-0.84) per 1 million population-years in 2009, peaking at 0.74 (95% CI: 0.65-0.84) in 2016 and declining to 0.03 (95% CI: 0.01-0.05) by 2022. Children aged 1-4 years had the highest incidence, and females had a slightly higher incidence rate than males, as indicated in outbreak-associated case data. Joinpoint incidence trends showed an annual percent change (APC) of 25.12% (95% CI: 11.47-53.76, p = 0.001) from 2009 to 2015, followed by a decline with an APC of -38.91% (95% CI: -60.07 to -29.57, p < 0.001). The outbreaks were predominantly person-to-person transmission, with the highest frequency occurring in childcare settings.

These findings underscore the need for targeted prevention strategies, such as ongoing hygiene education and sanitation enhancements in childcare, as well as reminders about Shigella prevention in shared educational facilities before the fall semester.