BACKGROUNDIn county-level tuberculosis (TB) dispensaries in China, the accurate diagnosis of sputum smear-negative pulmonary tuberculosis (SNPT) needs to be improved by developing and validating clinical and radiographic predictors.

METHODSThe study was conducted simultaneously in three counties per province in Chongqing Municipality and Liaoning Province in China between May 2005 and May 2006. A total of 432 new SNPT patients who are HIV-negative and more than 15 years old diagnosed by expert panels in county-level TB dispensaries were recruited. Their sputum samples were collected for culture before anti-TB treatment, and the treatment outcomes (changes of X-rays) were followed up at the end of the 6th month.

RESULTSOf the 432 SNPT patients, sputum culture positive (9.7%) or culture negative with good changes of X-rays at the end of the 6th month (73.6%) was validated as SNPT. Four predictive variables were associated with validated SNPT in the multivariate logistic regression model: age ≤55 years old (odds ratio (OR) 5.66; 95% CI 2.69-11.91), >60 days of cough (OR 3.73; 95% CI 1.10-12.65), ≥10% of pulmonary consolidation in the lungs (OR 5.40; 95% CI 2.90-10.06), and pulmonary consolidation in the upper lobe anterior segment (OR 3.00; 95% CI 1.57-5.72). The area under the receiver operating characteristic curve of the model was 0.77 (95% CI 0.71-0.83).

CONCLUSIONFour predictors of clinical and radiological characteristics that had a good diagnostic performance of SNPT deserve to be recommended as index indicators of SNPT diagnosis in county-level TB dispensaries in China.