Infectious Disease
Spatial, temporal, and space-time trends of reported Shigella spp. outbreaks in the United States, 2009-2022 Muhammad Rashid Bajwa* Muhammad Rashid Bajwa Bajwa Department of Pathobiology, University of Illinois Urbana Champaign, Urbana, IL, USA
Shigella spp. are the leading cause of acute gastroenteritis posing a public health concern in the United States. This study analyzed surveillance data on Shigella spp. outbreaks reported to the Centers for Disease Control and Prevention via the National Outbreak Reporting System from 2009 to 2022. A total of 1,208 outbreaks were reported across the 48 contiguous states and the District of Columbia, with outbreak incidence varying significantly across time and space. Incidence rates per million population 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. Moran’s I was used to identify local clusters and outliers, and Poisson spatial and space–time scan statistics were applied to detect areas and periods of significantly elevated or reduced outbreak rates. Shigella spp. outbreak incidence rates per 1 million population-years increased from 0.27 (95% CI: 0.01–0.84) in 2009 to a peak of 0.74 (95% CI: 0.65–0.84) in 2016, then declined to the lowest rate of 0.03 (95% CI: 0.01–0.05) by 2022. Joinpoint regression trends showed an annual percent change (APC) of 25.12% (95% CI: 11.47 to 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) from 2015 to 2022. Persistent high-rate spatial (relative risk, RR = 1.67–5.05) and space–time (RR = 2.28–12.87) clusters were identified in the Midwest, South, and Southwest, including Ohio, Texas, Minnesota, and Arizona. Collectively, these findings demonstrate that Shigella spp. outbreaks in the United States exhibit persistent and regionally distinct spatiotemporal clustering patterns. Identifying areas with sustained elevated outbreak risk can support targeted surveillance, prevention, and response efforts. These findings can guide public health authorities in exposure settings and region-specific Shigella spp. prevention policies across the US.