Polymerase Chain Reaction of secA1 on Sputum or Oral Wash Samples for the Diagnosis of Pulmonary Tuberculosis

Background. Nucleic acid amplification tests are sensitive and specific for identifying Mycobacterium tuberculosis in sputum smear-positive populations, but they are less sensitive in sputum smear-negative populations. Few studies have assessed their performance among patients infected with HIV, and no studies have assessed their performance with oral wash specimens, which may be easier to obtain than sputum samples. Methods. We performed a prospective study involving 127 adults from 2 populations who were undergoing evaluation for respiratory complaints at Mulago Hospital in Kampala, Uganda. We obtained and tested sputum samples for Mycobacterium tuberculosis, and we simultaneously obtained oral wash specimens to test for M. tuberculosis DNA by polymerase chain reaction (PCR) amplification of a novel locus, the secA1 gene. A positive mycobacterial culture of sputum was used to define cases of tuberculosis; we calculated the sensitivity and specificity of the PCR assay with sputum or oral wash specimens in reference to the standard of sputum culture results. Results. Tuberculosis (75 [59%] of 127 patients) and HIV infection (58 [46%] of 126 patients) were both common in the study population. PCR of sputum samples was highly sensitive (sensitivity, 99%; 95% confidence interval, 93%-100%) and specific (specificity, 88%; 95% confidence interval, 77%-96%) for detection of pulmonary tuberculosis and performed well among HIV-infected patients and among patients with negative sputum smear results. PCR of oral wash specimens was less sensitive (sensitivity, 73%; 95% confidence interval, 62%-83%) but also detected a substantial proportion of tuberculosis cases. Conclusions. PCR targeting the secA1 gene was highly sensitive and specific for identifying M. tuberculosis in sputum samples, independent of smear or HIV infection status. Oral washes showed promise as an easily obtained respiratory specimen for tuberculosis diagnosis. PCR of sputum for detection of the secA1 gene could be a rapid, effective diagnostic tool for tuberculosis referral centers.