Association of schistosomiasis with false positive HIV test

Association of schistosomiasis with false positive HIV test results in an African adolescent population.

The aim of the study was to investigate factors associated with the high rate of false positive test results observed on the 4(th) generation Murex HIV Ag/Ab Combination EIA when used in Tanzania. Clinical and socio-demographic factors associated with false positive HIV results were analysed in 6940 Tanzanian adolescents and young adults in the Northwestern region. Immunological factors, including IgG antibodies to malaria and schistosomiasis, heterophile antibody and rheumatoid factor titre, were analysed in a sub-sample of 284 Murex negative and 240 false positive sera. Conditional logistic regression was used to estimate odds ratios and 95% confidence intervals (CI). HIV false positive test results were associated with evidence of other infections. False positivity was strongly associated with increasing levels of Schistosoma haematobium worm IgG1, with adolescents with ODs in the top quartile at highest risk (adjusted OR=40.7, CI=8.5-194.2 compared with those in the bottom quartile). False positivity was also significantly associated with increasing S. mansoni egg IgG1, and RF titre >/= 80 (adjusted OR=8.2, CI=2.8-24.3). There was a significant negative association between Murex false positivity and levels of S. mansoni worm IgG1 and IgG2, and Plasmodium falciparum IgG1 and IgG4. In Africa, endemic infections may affect the specificity of immunoassays for HIV infection. Caution should be used when interpreting 4(th) generation HIV test results in African adolescent populations.

Editor’s note: Cross-reactivity between HIV-1 peptides and antibodies to Schistosoma appear to have contributed to the very high false positive HIV test results found among adolescents in this Tanzanian study. Pressure to develop highly sensitive HIV assays so that early infections are not missed has led to development of 4^th generation assays that detect both HIV antigen and HIV antibody. Such tests clearly don’t perform well in adolescents that are disproportionately affected by schistosomiasis. In this study, schistosomiasis IgG antibody was associated with Rheumatoid factor (RF) titres and these in turn were associated with false positive HIV test results. RF is found in autoimmune diseases such as rheumatoid arthritis but it is also associated with viral, bacterial, and other parasitic infections. Further research on the cross-reactivity of HIV diagnostic tests is warranted, with the findings used in the design and evaluation of tests specific for African populations.