Background: Tuberculosis (TB) is a mycobacterial infection mainly affecting the lungs. Early and correct diagnosis of sputum smear negative patients by chest radiography (CXR) is challenging since it depends on reader's ability to detect abnormal findings and to interpret it correctly.
Objectives: To evaluate the validity and reliability of CXR the diagnosis of TB among smear negative pulmonary tuberculosis (PTB).
Methods: An institutional based cross-sectional study was conducted at seven selected health facilities from October 2011 to September 2012 on 159 adults aged 18 years and above who were newly diagnosed smear negative for PTB patients diagnosed using Chest X-ray (CXR). Morning sputum was collected and cultured from each patient using Lowenstein Jensen media. All the CXRs were revised by senior radiologists in conjunction with the principal investigator. A structured questionnaire was used to collect socio-demographic, clinical and radiological data. Sensitivity and specificity measures of the CXR findings were calculated in comparison to the gold standard sputum culture results.
Results: The mean (SD) age of patients involved in the study was 37.1 (16.7), ranging from 18 to 87 years. Of the total 159 smear negative PTB patients, the most common CXR finding was consolidation (40.3%) followed by cavitations (23.9%) and nodular lesions (17.0%). Sputum culture results showed that, 47 (29.6%) were culture positive, 103 (64.7%) were culture negative and 9 (5.6%) were contaminated. About 14% (22/159) of the study subjects were HIV positive. The sensitivity and specificity of CXR findings were 77.1% (37/48) and 36.9% (41/111), respectively. The positive and negative predictive values were 34.6% (3 7/107) and 78.8% (41/52), respectively.
Conclusion: CXR can be used as supportive investigative modality to diagnose smear negative Pulmonary TB in conditions where TB culture is no more feasible.