In 2022, Burkholderia pseudomallei was first identified in continental United States (U.S.) environmental samples from the Mississippi Gulf Coast following two autochthonous infections. To better understand the extent of exposure to this emerging bacterium, we tested a convenience sample of 825 residual sera samples (550 from the Mississippi Gulf Coast, 275 from the northern U.S.) from a commercial diagnostic laboratory for the presence of antibodies to B. pseudomallei, using an indirect hemagglutination assay. We estimated seroprevalence of antibodies to B. pseudomallei in Mississippi Gulf Coast residents and in controls from northern regions of the U.S. where B. pseudomallei is less likely to persist in the environment. At a titer cut-off of ≥1:40, we observed a similar seropositivity between Mississippi Gulf Coast residents (14%, 95% CI: 11%, 17%) and controls (17%, 95% CI: 13%, 18%). Similarities in seropositivity suggest environmental exposure to B. pseudomallei in the Mississippi Gulf Coast may be limited; however, a lack of accompanying illness and exposure information limits our ability to conclusively interpret these findings. These estimates can serve as a baseline of seropositivity in the U.S. for future studies and to track the spread of B. pseudomallei in the U.S. over time.

Background: Hepatitis C is a public health threat with national elimination targets, yet prevalence is challenging to measure. We utilized a novel approach to estimate hepatitis C prevalence among adults using residual sera from a large commercial laboratory. Methods: We conducted a cross-sectional study in 50 states and the District of Columbia using a convenience sample of residual serum specimens (n = 81 483) among routine clinical specimens from adults aged 18–≤75 years. We randomly sampled within 2 age groups (18–≤49 years and 50–≤75 years) during November 2023–September 2024. Specimens were tested for hepatitis C virus (HCV) antibodies; reactive or equivocal results were reflexed to HCV ribonucleic acid (RNA) testing. We performed nested raking on the age–sex distribution of the United States. Results: Among adults aged 18–≤75 years, we estimated that the HCV antibody prevalence was 2.9% (95% CI, 2.8%–3.0%), corresponding to 6 887 000 (95% CI, 6 622 000–7 166 000) persons ever infected, and the HCV RNA prevalence was 0.7% (95% CI, .7%–.8%), corresponding to 1 698 000 (95% CI, 1 554 000–1 845 000) persons currently infected. Viral clearance was lower among younger adults (63.8% [95% CI, 60.6%–66.9%]) than older adults (81.1% [95% CI, 78.9%–83.3%]). Conclusions: In this analysis of residual sera from a commercial laboratory, we estimated that approximately 1.70 million adults were diagnosed with HCV infection during November 2023–September 2024. Although underlying selection bias limits generalizability to the US population, the substantial burden estimated after a decade of available curative treatment underscores the need for concerted nationwide hepatitis C elimination efforts.