Examination of the independent contribution of rheumatic heart disease and congestive cardiac failure to the development and outcome of melioidosis in Far North Queensland, tropical Australia

Abstract

Background Patients with rheumatic heart disease (RHD) and congestive cardiac failure (CCF) are believed to have an increased risk of melioidosis and are thought to be more likely to die from the infection. This study was performed to confirm these findings in a region with a high incidence of all three conditions. Principal findings Between January 1998 and December 2021 there were 392 cases of melioidosis in Far North Queensland, tropical Australia; 200/392 (51.0%) identified as an Indigenous Australian, and 337/392 (86.0%) had a confirmed predisposing comorbidity that increased risk for the infection. Overall, 46/392 (11.7%) died before hospital discharge; the case fatality rate declining during the study period (p for trend = 0.001). There were only 3/392 (0.8%) with confirmed RHD, all of whom had at least one other risk factor for melioidosis; all 3 survived to hospital discharge. Among the 200 Indigenous Australians in the cohort, 2 had confirmed RHD; not statistically greater than the prevalence of RHD in the local general Indigenous population (1.0% versus 1.2%, p = 1.0). RHD was present in only 1/193 (0.5%) cases of melioidosis diagnosed after October 2016, a period which coincided with prospective data collection. There were 26/392 (6.6%) with confirmed CCF, but all 26 had another traditional risk factor for melioidosis. Patients with CCF were more likely to also have chronic lung disease (OR (95% CI: 4.46 (1.93–10.31), pConclusions In this region of tropical Australia RHD and CCF do not appear to be independent risk factors for melioidosis and have limited prognostic utility. Author summary Melioidosis, a disease caused by Burkholderia pseudomallei, rarely develops in the absence of well-described predisposing conditions that include diabetes mellitus, hazardous alcohol intake, chronic kidney disease, chronic lung disease, malignancy, and immunosuppression. These comorbidities are also strongly linked to patients’ short and long-term outcomes. In the large Darwin Prospective Melioidosis Study (DPMS) performed in Australia’s Northern Territory, the presence of rheumatic heart disease (RHD) and/or congestive cardiac failure (CCF) were independently associated with pulmonary melioidosis and independently predicted death. Indeed, patients with RHD and/or CCF and melioidosis had the highest case-fatality rate in the DPMS cohort. The prevalence of RHD and/or CCF in cases of melioidosis in this study in Far North Queensland (FNQ), was similar to that seen in the Northern Territory. However, every patient had at least one other traditional risk factor for the disease. Furthermore, pulmonary involvement and mortality were not higher in patients with RHD and/or CCF. In FNQ, RHD and CCF are not independent risk factors for melioidosis and have limited prognostic utility. The high prevalence of these cardiac diseases in patients with melioidosis may be, at least partly, explained by the confounding presence of socioeconomic disadvantage that increases the incidence of all three conditions.