Diagnosing pulmonary tuberculosis (PTB) remains a major public health challenge partly because of slow culture growth. Because sputum acid fast bacilli (AFB) smear may be negative despite active infection, many cases of TB remain unidentified at the time of initial screening. This is of greater concern in high risk HIV/AIDS patients. Therefore, we sought to evaluate the correlation between sputum AFB smear and sputum MTB culture to determine the effect of HIV infection on this screening strategy.
Retrospective chart review of PTB infections in a major county hospital in the southeastern USA during the period of January 2006 to December 2008. Overall sensitivity and specificity of sputum AFB smear were determined using sputum MTB culture results as the gold standard. We also assessed the effects of HIV status, gender and race on both sensitivity and specificity.
A total of 89 patients were included in the final analysis. The mean age was 47.1years; 56.2% had HIV infection; 61.8% of patiens were men; and 80.9% were black. Overall sensitivity of sputum AFB smear versus sputum MTB culture was 67.7% [95% confidence interval 48.5% –82.7%] and the specificity was 82.8% [95% confidence interval 70.1% –91.0%]. A non-significant diagnostic discordance was noted between sputum AFB smear versus sputum MTB culture for HIV(+) and HIV(−) patients, sensitivity 58.3% versus 70.6%, p = 0.561 and specificity 84.2% versus. 73.3%, respectively. Diagnostic discordance was not present in the analyses stratified by gender or race.
Our study suggests that AFB sputum smears in HIV patients may be less sensitive when screening for PTB compared to screening in non-HIV patients. Although the differences were not statistically significant, our study was retrospective. We conclude that a larger propsective investigation is needed to assess the screening of HIV patients for PTB.
Amongst our HIV patients, more cases of PTB are missed based on sputum smear screening alone, potentially resulting in more exposure of health care personnel and the general population.
Eric Flenaugh, No Financial Disclosure Information; No Product/Research Disclosure Information