The effect of HIV and antiretroviral therapy on characteristics of pulmonary tuberculosis in northern Malawi: a cross-sectional study

Background: HIV infection reduces the likelihood that individuals with pulmonary tuberculosis are smear positive and that they have cavitatory disease. Antiretroviral therapy (ART) may shift the pattern of disease to be more similar to that of HIV negative patients. This would aid diagnosis- which often depends on sputum smears – but would also increase infectiousness. We assessed the effect of HIV and ART on smear positivity and cavitatory disease in laboratory-confirmed pulmonary TB patients. Methods: Three sputum samples were collected per pulmonary TB suspect and were examined using microscopy and culture. Chest radiographs were available for a subset of patients as part of another study. The effect of HIV and ART status on sputum smear positivity and lung cavitation were evaluated using multivariable logistic regression. Results: Of 1024 laboratory-confirmed pulmonary TB patients who were identified between January 2005 and December 2011, 766 had HIV and ART status available. Positive sputum smears were significantly more common among HIV negative individuals than HIV positive individuals (adjusted OR = 2.91, 95% CI 1.53 – 5.55). Compared to those HIV positive but not on ART, patients on ART were more likely to be smear positive (adjusted OR = 2.33, 95% CI 1.01 – 5.39) if they had been on ART ≤ 6 months, but only slightly more likely to be smear positive (adjusted OR = 1.43, 95% CI 0.68 – 2.99) if they were on ART > 6 months. HIV negative patients were more likely than HIV positive patients to have cavitatory disease (adjusted OR = 1.97, 95% CI 1.20 – 3.23). Patients on ART > 6 months had a slight increase in cavitatory disease compared to HIV positive patients not on ART (adjusted OR = 1.68, CI 0.78 – 3.63). Conclusions: HIV infection is associated with less smear positivity and cavitation in pulmonary TB patients. Among HIV positive patients, the use of ART shifts the presentation of disease towards that seen in HIV-negative individuals, which facilitates diagnosis but which also could increase infectiousness