Sensitivity of direct versus concentrated sputum smear microscopy in HIV-infected patients suspected of having pulmonary tuberculosis
- Equal contributors
1 Division of Pulmonary and Critical Care Medicine, University of California, San Francisco, CA, USA
2 MU-UCSF Research Collaboration, Kampala, Uganda
3 MU-UCSF Research Collaboration, CA, San Francisco, USA
4 Francis J. Curry National Tuberculosis Center, San Francisco, CA, USA
5 Department of Medicine, University of California, San Francisco, San Francisco, CA, USA
6 Faculty of Medicine, Makerere University, Kampala, Uganda
7 Department of Microbiology, Makerere University, Kampala, Uganda
8 HIV/AIDS Division, University of California, San Francisco, CA, USA
BMC Infectious Diseases 2009, 9:53 doi:10.1186/1471-2334-9-53Published: 6 May 2009
Sputum concentration increases the sensitivity of smear microscopy for the diagnosis of tuberculosis (TB), but few studies have investigated this method in human immunodeficiency virus (HIV)-infected individuals.
We performed a prospective, blinded evaluation of direct and concentrated Ziehl-Neelsen smear microscopy on a single early-morning sputum sample in HIV-infected patients with > 2 weeks of cough hospitalized in Kampala, Uganda. Direct and concentrated smear results were compared with results of Lowenstein-Jensen culture.
Of 279 participants, 170 (61%) had culture-confirmed TB. The sensitivity of direct and concentrated smear microscopy was not significantly different (51% vs. 52%, difference 1%, 95% confidence interval (CI): [-7%, 10%], p = 0.88). However, when results of both direct and concentrated smears were considered together, sensitivity was significantly increased compared with either method alone (64%, 95% CI: [56%, 72%], p < 0.01 for both comparisons) and was similar to that of direct smear results from consecutive (spot and early-morning) specimens (64% vs. 63%, difference 1%, 95% CI: [-6%, 8%], p = 0.85). Among 109 patients with negative cultures, one had a positive direct smear and 12 had positive concentrated smears (specificity 99% vs. 89%, difference 10%, 95% CI: [2%, 18%], p = 0.003). Of these 13 patients, 5 (38%) had improved on TB therapy after two months.
Sputum concentration did not increase the sensitivity of light microscopy for TB diagnosis in this HIV-infected population. Given the resource requirements for sputum concentration, additional studies using maximal blinding, high-quality direct microscopy, and a rigorous gold standard should be conducted before universally recommending this technique.