Background: In 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.
Methods: The 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.
Results: Of 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).
Conclusion: Four 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.