Background: Infection with the gram-negative bacterium Burkholderiapseudomallei can result in melioidosis, a life-threatening disease that can bedifficult to diagnose. Culture remains the gold standard for diagnosis butrequires laboratory resources not available in many endemic regions. A lateralflow immunoassay has shown promise for POC diagnostics but suffers from lowsensitivity when used on blood samples. PCR also has low sensitivity on blood,attributed to the low bacterial numbers in blood observed in melioidosis patients,even when bacteraemic.
Methods: A prototype i-STAT cartridge was developed to utilizethe monoclonal antibody specific for the capsule of pathogenic Burkholderiaspecies employed on the LFI. The resulting POC assay was evaluated on 414clinical specimens from Darwin, Australia and Cambodia.
Results: The i-STAT assay accurately distinguished Australian bloodculture positive melioidosis patients from Australian patients hospitalizedwith other infections (AUC = 0.91, 95% CI 0.817 - 1.0). We derived an assaycutoff with 76% sensitivity and 94% specificity that correctly classified 88%(n=74) of the Australian patients. Interestingly, only 46% (6/13) of theculture-positive melioidosis patients in Cambodia were classified correctly. Ofgreat importance however, the assay detected capsule from blood samples for 32%of blood culture negative melioidosis patients in both cohorts and previouslyundiagnosed melioidosis patients in Cambodia. In addition the assay showed highsensitivity and specificity for urine, pus and sputum.
Conclusions: Diagnostic tools that are not dependent upon the growthkinetics or the levels of bacteremia of B. pseudomallei represent thenext-generation of diagnostics and must be pursued further.