The Use of Positive Serological Tests as Evidence of Exposure to Burkholderia pseudomallei

We note with interest Rolim and colleagues’ cross-sectional serosurvey of residents of Tejuçuoca and Banabuiu in Ceará, Brazil to provide evidence of exposure to Burkholderia pseudomallei , the causative agent of melioidosis. 1 Although there is definitive evidence of culture-confirmed melioidosis in that region, 2 we caution against the use of an unvalidated enzyme-linked immunosorbent assay (ELISA) such as that used by Rolim and others to provide evidence of widespread exposure. Although all serological tests are of relatively limited value for the diagnosis of melioidosis in patients living in areas where melioidosis is endemic (primarily because of seropositivity in the healthy population), the indirect hemagglutination assay (IHA) is widely accepted as the serological test of choice. The diagnostic performance of the IHA has been defined by several studies that used different cutoffs to take account of variable rates of background seropositivity. In the endemic region of Australia, the diagnostic sensitivity of an IHA titer of ≥ 1:40 was 56% at the time of admission (using culture as the gold standard), with evidence of subsequent seroconversion on serial IHA testing in 68% of patients who were initially IHA negative. 3 In northeast Thailand, the diagnostic sensitivity of the much higher IHA titer of ≥ 1:160 was 72% and the specificity 64%. 4 Other assays have been evaluated but have only been found to offer a marginal improvement on the IHA. 5