Sputum microscopy for the diagnosis of HIV-associated pulmonary tuberculosis in Tanzania.
BACKGROUND
In many resource poor settings only sputum microscopy is employed for the diagnosis of HIV-associated pulmonary tuberculosis; sputum culture may not be available.


METHODS
We determined the diagnostic accuracy of sputum microscopy for active case finding of HIV-associated pulmonary tuberculosis using TB culture as the reference standard.


RESULTS
2216 potential subjects screened for a TB vaccine trial submitted 9454 expectorated sputum specimens: 212 (2.2%) were sputum culture positive for Mycobacterium tuberculosis (MTB), 31 (0.3%) for non-tuberculous mycobacteria, and 79 (0.8%) were contaminated. The overall sensitivity of sputum microscopy was 61.8% (131/212) and specificity 99.7% (9108/9132). Sputum microscopy sensitivity varied from 22.6% in specimens with < 20 colony forming units (CFU)/specimen to 94.2% in patients with > 100 CFU/specimen plus confluent growth. The incremental diagnostic value for sputum microscopy was 92.1%, 1.8% and 7.1% for the first, second and third specimens, respectively. The positive predictive value and negative predictive values for sputum microscopy were 84.5% and 99.1%, respectively. The likelihood ratio (LR) of a positive sputum microscopy was 235.1 (95% CI 155.8 - 354.8), while the LR of a negative test was 0.38 (95CI 0.32 - 0.45). The 212 positive sputum cultures for MTB represented 103 patients; sputum microscopy was positive for 57 (55.3%) of 103 patients.


CONCLUSIONS
Sputum microscopy on 3 expectorated sputum specimens will only detect 55% of culture positive HIV-infected patients in active screening for pulmonary tuberculosis. Sensitivity is higher in patients with greater numbers of CFUs in the sputum. Culture is required for active case finding of HIV- associated pulmonary tuberculosis.
Matee
Mecky
M
Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania. mmateerrr@yahoo.com
Mtei
Lillian
L
Lounasvaara
Tarja
T
Wieland-Alter
Wendy
W
Waddell
Richard
R
Lyimo
Johnson
J
Bakari
Muhammad
M
Pallangyo
Kisali
K
von Reyn
C Fordham
CF
D017088:AIDS-Related Opportunistic Infections / Q000175:diagnosis* / Q000382:microbiology; D015169:Colony Count, Microbial; D046508:Culture Techniques; D005260:Female; D015658:HIV Infections / Q000150:complications*; D015528:HIV Seroprevalence; D006801:Humans; D008297:Male; D008853:Microscopy; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D013636:Tanzania; D014397:Tuberculosis, Pulmonary / Q000150:complications / Q000175:diagnosis* / Q000382:microbiology