Background: Tuberculosis (TB) diagnosis in most resource-limited settings still depends on smear microscopy for identification of acid-fast bacilli (AFB). However, recently developed molecular diagnostics that test for the presence of Mycobacterium tuberculosis (Mtb) DNA have been shown to be superior for confirmation of TB diagnosis.
Methods: At regular clinical visits over a 12-month period, we collected sputa from HIV-infected patients presenting with signs or symptoms of TB at 2 Nigerian clinics. Sputa were stained for AFB and tested using the Genotype MTBDRplus to confirm the presence of Mtb. Other species were identified using 16S rRNA sequence.
Results: In 56% (233/415) of AFB-positive patients, Mtb was confirmed. The patients on antiretroviral therapy were less likely than those not on antiretroviral therapy to be infected with Mtb [odds ratio (OR) = 0.25, P = 0.003]. In a multivariate logistic regression model using clinical features and diagnostic results, abnormal respiratory findings on auscultation (OR = 3.28, P = 0.03) and a direct sputum smear grade >3/100 (OR = 6.4, 4.6, P < 0.02) were significant predictors of Mtb infection. Concentrated sputum smear was predictive of Mtb infection only at the highest grades (2+, 3+). Interestingly, among 65 samples that could not be confirmed for Mtb, 32 (49%) were found to contain other, possibly novel, actinomycetes, including atypical Mycobacteria, Rhodococcus spp, Nocardia spp, and Corynebacterium spp.
Conclusions: We conclude that concentrated sputum smears may misidentify other bacteria as Mtb in HIV-infected patients. The use of molecular diagnostics could reduce unnecessary or inappropriate treatment and improve identification of pathogens in resource-limited settings with high HIV burden.
*Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA;
†Research Division and
‡Clinical Sciences Division, Nigerian Institute of Medical Research (NIMR) Lagos, Nigeria;
§AIDS Prevention Initiative in Nigeria, Abuja, Nigeria; and
the Departments of ‖Medicine and
¶Medical Microbiology, Jos University Teaching Hospital, Jos, Nigeria.
Correspondence to: Phyllis J. Kanki, DVM, SD, Department of Immunology and Infectious Diseases, Harvard School of Public Health, 651 Huntington Avenue, FXB 405, Boston, MA 02115 (e-mail: firstname.lastname@example.org).
Supported by the US Department of Health and Human Services, Health Resources and Services Administration (U51HA02522-01-01). Support for L. Dinic was provided by the Zlatko and Balokovic Scholarship, the Uwe Brinkmann Travel Grant, and the Harvard University Science and Engineering Committee.
The authors have no conflicts of interest to disclose.
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Presented at the AIDS 2012, XIX International AIDS conference in Washington, DC, on July 25, 2012 (Abstract WEPE038), and ASLM in Cape Town South Africa on December 6, 2012 (Abstract 1238).
Received October 29, 2012
Accepted January 23, 2013