Impact of human immunodeficiency virus and CD4 count on tuberculosis diagnosis: analysis of city-wide data from Cape Town, South Africa

Abstract

The impact of human immunodeficiency virus (HIV) infection and CD4 count on the diagnosis of tuberculosis (TB) at population level is incompletely defined. To determine how HIV infection and CD4 count affect disease site, sputum smear status and overall rate of laboratory confirmation (sputum smear microscopy or culture) of TB cases under routine programme conditions. Retrospective analysis of the 2009 electronic TB register for Cape Town, South Africa. Of 29,478 TB cases notified in 2009, HIV status was known for 25,744 (87.3%) cases, of whom 13,237 (51.4%) were HIV-positive. Of these, 61.2% had CD4 cell counts of <200 cells/μl and 82.7% had counts of <350 cells/μl. Laboratory confirmation of TB (by smear or culture) was obtained less frequently in HIV-infected than non-HIV-infected adult cases (53.9% vs. 74.3%, P< 0.001). HIV infection was associated with a higher proportion of sputum smear-negative and extra-pulmonary TB and lower grades of sputum smear positivity even among those with CD4 counts of ≥ 500 cells/μl. However, the relationship between the proportion of smear-positive cases and CD4 count was non-linear. Much TB is not laboratory-confirmed in this setting despite good laboratory services. HIV-associated TB is more difficult to diagnose even at high CD4 cell counts of >500 cells/μl, suggesting early impact after HIV seroconversion.