Hospital-Based Cross-Sectional Study of Burkholderia pseudomallei Seroreactivity Among Febrile Patients in Northernmost Vietnam: Near-Neighbor Bloodstream Isolates, Environmental Correlates, and Spatial Clustering.

Melioidosis is a potentially fatal tropical disease caused by the environmentally mediated bacterium, Burkholderia pseudomallei. In Vietnam, melioidosis is not nationally reportable and little is known regarding its epidemiology and distribution in the northernmost mountainous provinces. To address this gap, a hospital-based cross-sectional study was conducted across six northernmost provinces of Vietnam: Son La, Dien Bien, Lai Chau, Lao Cai, Ha Giang, and Cao Bang. Objectives were to (a) elucidate the distribution and environmental correlates of B. pseudomallei seroreactivity, and (b) identify bacteria isolated from subset of admitted patients. Burkholderia pseudomallei-specific IgG ELISAs were used to identify elevated serological responses in febrile (≥38°C, unknown cause) hospital patients (n = 2,440; 2020-2023). Exploratory blood culturing and whole genome sequencing (WGS) from a small subset of patients was performed. A commune-scale presence-absence analysis examined environmental associations to seropositivity via a generalized linear model with Moran's eigenvector spatial filtering. Spatial distributions of the proportion of patients IgG seropositive (+2 SD above mean) to Hcp1/OPS were smoothed using spatial Bayes and clusters were detected with local Moran's I. WGS revealed B. pseudomallei near-neighbor species in some blood cultures; organisms that persist in similar environments, infect opportunistically, and are difficult to diagnose. A seasonal pattern was identified with more seropositivity among febrile hospital patients admitted in the wet season. At commune-scale, seropositivity correlated to higher rainfall averages, proximity to major waterways, and low soil nutrients. Seropositivity was spatially heterogeneous and several spatial clusters (seropositivity hotspots) were detected, indicating a need for local or regional surveillance.