Melioidosis Queensland: An analysis of clinical outcomes and genomic factors.

Background: The clinical and genomic epidemiology of melioidosis varies across regions. Aim: To describe the clinical and genetic diversity of B. pseudomallei across Queensland, Australia. Methods: Whole genome sequencing of clinical isolates stored at the melioidosis reference lab from 1996–2020 was performed and analysed in conjunction with available clinical data. Results: Isolates from 292 patients were analysed. Bacteraemia was present in 71% and pneumonia in 65%. The case-fatality rate was 25%. Novel sequence types (ST) accounted for 51% of all isolates. No association was identified between the variable virulence factors assessed and patient outcome. Over time, the proportion of First Nation's patients declined from 59% to 26%, and the proportion of patients aged >70 years rose from 13% to 38%. Conclusion: This study describes a genomically diverse and comparatively distinct collection of B. pseudomallei clinical isolates from across Queensland, Australia. An increasing incidence of melioidosis in elderly patients may be an important factor in the persistently high case-fatality in this region and warrants further investigation and directed intervention. Author summary: Burkholderia pseudomallei is an environmental bacteria found in the soil and water of tropical and subtropical regions. This organism causes melioidosis, an infectious disease that often results in pneumonia and bloodstream infections. Previous studies have suggested a relationship between specific bacterial genetic factors and disease outcomes. This study reports on the clinical and bacterial genetic factors associated with disease outcomes in Queensland, Australia. A total of 292 patients and the associated bacterial isolates obtained from them during their hospital admission were analysed. The majority of patients presented with pneumonia and had a bloodstream infection. The case-fatality rate improved slightly over time but remains higher than other regions in Australia. Over the period of the study the proportion of First Nation's people affected decreased significantly. Notably, for reasons yet to be determined, the proportion of patients aged over 70 years increased over time. The bacterial genetic data demonstrate a high level of diversity across the region, however there was no association between previously described virulence genes and clinical outcomes in our cohort. This study creates a platform for further state-wide melioidosis research in Queensland. [ABSTRACT FROM AUTHOR]