Evaluation of a Histoplasma antigen Lateral Flow Assay for the rapid diagnosis of progressive disseminated histoplasmosis in AIDS patients

Objectives: Histoplasmosis is an important cause of mortality in persons living with HIV and AIDS (PLWHA), especially in countries where patients have limited access to antiretroviral therapies and diagnostic testing. In PLWHA, the progressive disseminated form of histoplasmosis (PDH) can be fatal without treatment. Early diagnosis is critical for providing proper treatment, however, current diagnosis by culture can take weeks and serology may be falsely negative early in infection or as a result of immunosuppression in these patients. Detection of Histoplasma antigen in patient specimens improves sensitivity and timeliness of diagnosis, but the current method by enzyme immunoassay must be performed by highly trained personnel in specialty laboratories.  Recently, the development of the lateral flow technology has provided a method that is simple to use and can be performed in a setting closer to the patient. In this study, a lateral flow assay (LFA) was evaluated for the detection of Histoplasma antigen in sera. 

Methods: Using a MiraVista Diagnostics LFA for detection of Histoplasma antigen, we evaluated 47 serum samples: 19 from patients with AIDS and culture-proven PDH and 28 from patients with other fungal and bacterial infections, as well as healthy people. LFA devices were read by human eye and automated reader. 

Results: When the LFA test was read by human eye, sensitivity was 95% and specificity was 82%. Using an automated reader, sensitivity was 89% and specificity was 89%. The Kappa index compared human eye and automated reader was 0.87. Cross-reactions were observed principally in samples from patients with proven diagnosis of paracoccidioidomycosis. 

Conclusion: The MiraVista Diagnostics LFA had high analytical performance and good agreement between human eye and automated reader. This LFA allows Histoplasma antigen testing with minimal laboratory equipment and infrastructure requirements. Based on these results, this new method is a viable option for rapid diagnosis of PDH. LFA provides highly sensitive results in <1 hour, being faster and more sensitive for PDH than other immunological assays, such as ELISA (three to five hours; >90% sensitivity), immunodiffusion and complement fixation (two days; ~65% sensitivity), and conventional microbiological tests, including histopathologic examination (one to two days; ~75% sensitivity) and culture (two to four weeks; ~80% sensitivity). Prompt diagnosis of PDH could impact public health by initiating early treatment thereby reducing mortality.