Effect of Antiretroviral Therapy on the Diagnostic Accuracy of Symptom Screening for Intensified Tuberculosis Case Finding in a South African HIV Clinic

Background. Current symptom screening algorithms for intensified tuberculosis case finding or prior to isoniazid preventive therapy (IPT) in patients infected with human immunodeficiency virus (HIV) were derived from antiretroviral-naive cohorts. There is a need to validate screening algorithms in patients on antiretroviral therapy (ART). Methods. We performed cross-sectional evaluation of the diagnostic accuracy of symptom screening, including the World Health Organization (WHO) algorithm, to rule out tuberculosis in HIV-infected individuals pre-ART and on ART undergoing screening prior to IPT. Results. A total of 1429 participants, 54% on ART, had symptom screening and a sputum culture result available. Culture-positive tuberculosis was diagnosed in 126 patients (8.8%, 95% confidence interval [CI], 7.4%-10.4%). The WHO symptom screen in the on-ART compared with the pre-ART group had a lower sensitivity (23.8% vs 47.6%), but higher specificity (94.4% vs 79.8%). The effect of ART was independent of CD4(+) count in multivariable analyses. The posttest probability of tuberculosis following a negative WHO screen was 8.9% (95% CI, 7.4%-10.8%) and 4.4% (95% CI, 3.7%-5.2%) for the pre-ART and on-ART groups, respectively. Addition of body mass index to the WHO screen significantly improved discriminatory ability in both ART groups, which was further improved by adding CD4 count and ART duration. Conclusions. The WHO symptom screen has poor sensitivity, especially among patients on ART, in a clinic where regular tuberculosis screening is practiced. Consequently, a significant proportion of individuals with tuberculosis would inadvertently be placed on isoniazid monotherapy despite high negative predictive values. Until more sensitive methods of ruling out tuberculosis are established, it would be prudent to do a sputum culture prior to IPT where this is feasible.