Importance of blood samples for diagnosis and drug sensitivity testing in HIV positive patients with suspected tuberculosis.

Diagnosis of tuberculosis is difficult in HIV positive patients since they often present with atypical symptoms and are susceptible to pulmonary infections that mimic tuberculosis. Sputum collection may not be possible even in patients with pulmonary involvement since a productive cough is not always present. In such patients blood smear and culture for AFB apart from serving as a diagnostic tool can be used for testing drug sensitivity. This study was undertaken to explore the value of blood culture for diagnosis in patients with suspected TB. In addition a comparison of drug sensitivity patterns of blood and sputum isolates in 10 of these patients was also carried out. Methods: Blood and sputum samples were processed cultured and isolates tested for their drug susceptibility and for niacin production nitrate reduction as well as catalase activity at 68°C. All 24 blood samples were culture positive although only 6 were smear positive. On the basis of the biochemical investigations 22 strains were identified as Mycobacterium tuberculosis. All the 10 sputum samples were culture positive despite 4 being smear negative. Comparison of drug sensitivity profiles from blood and sputum revealed concordance to five first or second line drugs in 5 of 10 patients. Additionally 2 patients demonstrated discordance for only one first or second line drug. The study demonstrates the importance of blood culture in confirming diagnosis of tuberculosis and testing for drug sensitivity in HIV positive patients without a productive cough. The level of discordance in drug sensitivity profiles between blood and sputum the same individual is suggestive of infection with multiple strains. Testing for the occurrence of multistrain infections through individual colony examination of a single isolate is necessary since such infections would affect treatment of non-responder patients having HIV-TB dual infections. (authors)