Diagnosing smear-negative tuberculosis using case definitions and treatment response in HIV-infected adults

Abstract

Objective: To assess the diagnostic utility of expanded case definitions for HIV-associated smear-negative pulmonary tuberculosis (PTB) and extra-pulmonary TB (EPTB), and to derive objective criteria for response to anti-tuberculosis treatment.

Design: A prospective cohort study of HIV-infected adults who met expanded clinical case definitions for smear-negative PTB and EPTB.

Methods: All participants were started on rifampicin-based anti-tuberculosis treatment after mycobacterial cultures from multiple sites. At weeks 2, 4 and 8, response to treatment (RTT) was assessed by measuring changes in weight, haemoglobin, C-reactive protein, Karnofsky performance score and symptom count ratio.

Results: Of 147 participants enrolled, 105 (71%) were diagnosed with definite (culture-positive) or probable (histological features) TB and 25 (17%) with possible TB (treatment response). The positive predictive value for the most common case definitions ranged from 89% to 96%. Significant improvements in all the RTT parameters occurred in the subjects with confirmed TB (P < 0.001). Clinically relevant RTT criteria were derived, two or more of which were met at week 8 in 97.5% of subjects with confirmed TB, 91.3% of subjects with possible TB and none of the subjects without TB.

Conclusion: Expanded case definitions could enhance the diagnosis of PTB and EPTB in HIV-infected adults in resource-limited settings. Using objective criteria, RTT can be assessed within 8 weeks of initiating anti-tuberculosis treatment.