Can urinary histoplasma antigen test improve the diagnosis of histoplasmosis in a tuberculosis endemic region?

Background: Many patients with histoplasmosis are treated with anti-tubercular therapy (ATT) in tuberculosis endemic regions as diagnosis of histoplasmosis requires invasive sampling. We sought to study the utility of urinary Histoplasma antigen detection test.

Methods: Case records of patients with a diagnosis of histoplasmosis prior to (Period A) and after (Period B) introduction of urinary Histoplasma antigen detection test were analysed in this single centre retrospective study.

Results: Thirty-seven patients (18 in Period A, and 19 patients in Period B) were studied. There was nearly a threefold increase in diagnoses (from 0.39 cases to 1.18 cases per month) after the introduction of antigen test. Nine patients (24.3%) were immunocompromised (6 had HIV infection and 3 were on steroids), and 28 (75.6%) were immunocompetent. Empirical ATT had been given to 10 patients prior to histoplasmosis diagnosis. Invasive tissue sampling was required in only two patients in Period B to confirm the diagnosis. Immunocompromised patients were younger, were more likely to have skin and mucosal findings, anaemia and leucopenia as compared to immune-competent patients.

Conclusion: This study emphasises that histoplasmosis cases may be missed and patients may receive ATT unnecessarily. Histoplasma antigen increased the diagnostic yield by almost threefold in our study.