Abstract
BackgroundChest radiography to diagnose and screen for pulmonary tuberculosis has limitations, especially due to inter-reader variability. Automating the interpretation has the potential to overcome this drawback and to deliver objective and reproducible results. The CAD4TB software is a computer-aided detection system that has shown promising preliminary findings. Evaluation studies in different settings are needed to assess diagnostic accuracy and practicability of use.MethodsCAD4TB was evaluated on chest radiographs of patients with symptoms suggestive of pulmonary tuberculosis enrolled in two cohort studies in Tanzania. All patients were characterized by sputum smear microscopy and culture including subsequent antigen or molecular confirmation of Mycobacterium tuberculosis (M.tb) to determine the reference standard. Chest radiographs were read by the software and two human readers, one expert reader and one clinical officer. The sensitivity and specificity of CAD4TB was depicted using receiver operating characteristic (ROC) curves, the area under the curve calculated and the performance of the software compared to the results of human readers.ResultsOf 861 study participants, 194 (23%) were culture-positive for M.tb. The area under the ROC curve of CAD4TB for the detection of culture-positive pulmonary tuberculosis was 0.84 (95% CI 0.80–0.88). CAD4TB was significantly more accurate for the discrimination of smear-positive cases against non TB patients than for smear-negative cases (p-value<0.01). It differentiated better between TB cases and non TB patients among HIV-negative compared to HIV-positive individuals (p<0.01). CAD4TB significantly outperformed the clinical officer, but did not reach the accuracy of the expert reader (p = 0.02), for a tuberculosis specific reading threshold.ConclusionCAD4TB accurately distinguished between the chest radiographs of culture-positive TB cases and controls. Further studies on cost-effectiveness, operational and ethical aspects should determine its place in diagnostic and screening algorithms.
Highlights
The role and potential of chest radiography as a diagnostic and screening tool for pulmonary tuberculosis (PTB) has long been debated
Study Population This validation study was done on chest radiographs of participants from two cohort studies (TB Cohort and TB CHILD study) which have been conducted at the TB Clinic of the Ifakara Health Institute (IHI) in Bagamoyo, Tanzania
All adult patients from both studies were eligible for the CAD4TB validation study if they initially presented with persistent cough of 2 weeks or more and at least one of the following TB associated findings: haemoptysis, chest pain, fever, night sweats, constant fatigue, recent unexplained weight loss, loss of appetite, malaise or contact with a known TB case
Summary
The role and potential of chest radiography as a diagnostic and screening tool for pulmonary tuberculosis (PTB) has long been debated. As a rapid examination that can be interpreted on-site with a high sensitivity (between 74 and 90% for PTB related abnormalities, up to 97%, if any abnormality is considered [1,2,3,4]), it has a firm place in the diagnosis of pulmonary tuberculosis. Interpreting chest radiographs is complex and subjective: it is a two dimensional representation of a three dimensional structure, and there are varied manifestations of PTB. The complexity of the interpretation code and the structure of the report form affect the result [5,6]. Chest radiography to diagnose and screen for pulmonary tuberculosis has limitations, especially due to interreader variability. Evaluation studies in different settings are needed to assess diagnostic accuracy and practicability of use
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