What causes smear-negative pulmonary tuberculosis in Malawi, an area of high HIV seroprevalence?

SETTING

The Central Hospital and the District Tuberculosis (TB) Registry in Lilongwe, the capital of Malawi. In this setting smear-negative pulmonary tuberculosis (PTB) is diagnosed using clinical and radiographic criteria for TB, and mycobacterial cultures are not routinely available.

OBJECTIVE

To determine the proportion of patients being registered for smear-negative PTB treatment in Lilongwe who have TB that can be confirmed microbiologically.

DESIGN

Prospective cohort study of patients about to start treatment under operational conditions for smear-negative PTB in Lilongwe between October 1997 and June 1998. Patients referred to the study team underwent a detailed clinical re-assessment, testing for human immunodeficiency virus (HIV), repeat sputum smear microscopy for acid-fast bacilli and mycobacterial cultures of sputum and blood. Bronchoscopy and bronchoalveolar lavage (BAL) were performed and BAL fluid was examined for TB, Pneumocystis carinii and other fungi.

RESULTS

Of 352 smear-negative PTB suspects assessed, the diagnosis of TB was confirmed in 137 (39%) cases. Eighty-nine per cent of patients assessed were HIV-positive, of whom 81% met the expanded case definition for the acquired immune-deficiency syndrome (AIDS).

CONCLUSION

TB was the most commonly confirmed diagnosis amongst patients about to start treatment for smear-negative PTB in an area of high background HIV seroprevalence.