Performance of Interferon-Gamma and IP-10 Release Assays for Diagnosing Latent Tuberculosis Infections in Patients with Concurrent Malaria in Tanzania

Interferon-gamma (IFN-gamma) release assays (IGRAs) are used to detect cellular immune recognition of Mycobacterium tuberculosis. The chemokine IFN-gamma-inducible protein 10 (IP-10) is an alternative diagnostic biomarker to IFN-gamma. Several conditions interfere with IGRA test performance. We aimed to assess the possible influence of Plasmodium falciparum infection on the IGRA test QuantiFERON-TB GOLD In-Tube (QFT) test and an in-house IP-10 release assay. In total, 241 Tanzanian adults were included; 184 patients with uncomplicated malaria (88 human immunodeficiency virus [HIV] coinfected) and 57 HIV -infected patients without malaria infection. Malaria was treated with artemether-lumefantrine (Coartem (R)). QFT testing was performed before initiation of malaria treatment and at days 7 and 42. In total, 172 patients completed follow-up. IFN-gamma and IP-10 was measured in QFT supernatants. We found that during malaria infection IFN-gamma and IP-10 levels in the unstimulated samples were elevated, mitogen responsiveness was impaired, and CD4 cell counts were decreased. These alterations reverted after malaria treatment. Concurrent malaria infection did not affect QFT test results, whereas there were more indeterminate IP-10 results during acute malaria infection. We suggest that IGRA and IP-10 release assay results of malaria patients should be interpreted with caution and that testing preferably should be postponed until after malaria treatment.