Comparative study of DR and CT in the application of close contacts screening for tuberculosis outbreaks

ObjectiveTo assess the value of direct digital radiography (DR) and CT in the screening of tuberculosis.MethodsIn a tuberculosis outbreak in May, 2014, both chest DR and CT were taken in the close contacts (n = 35 cases). The chi square test and ROC curve were used to evaluate and calculate the missed pulmonary lesions from DR and the natures of these lesions.ResultsAbnormal shadow detection rates of chest DR and CT were 22.9% (8/35) and 40% (14/35) respectively, the difference was statistically significant (χ2 = 16.154, P < 0.01). In the 6 missed cases from chest DR, 3 cases showed with anatomical occult or overlap, such as local area between azygos vein and esophagus (1 case), lung markings in the lower lobe (1 case) and diaphragmatic occlusion(1 case); and in the other 3 missed cases, early signs of small nodules or tree-in-bud were the major signs. ROC analysis showed that when the axis of tree-in-bud is less than 22 mm, it was prone to produce misdiagnosis by using the chest DR. The area under the ROC curve (AUC) was 0.925 with the sensitivity of 90% and specificity of 83.3%. In the 14 cases detected on CT, the lung was involved in 12 cases and the pleura was involved in 2 cases. For the 12 lung-involved cases, the lesions involving from one lung segment to five lung segments were occurred in 6 cases (50.0%), 2 cases (16.7%), 1 case (8.3%), 1 case (8.3%), and 2 cases (16.7%), respectively. Tree-in-bud signs were the main CT characteristics in close contacts, and accounted for about 91.7% (11/12). All the 4 pleura-involved cases showed pleural thickening and pleural tuberculoma after 3–4 months' anti-TB therapy. In the 14 cases detected by CT, 6 cases with micro-lesions were taken by anti-TB experimental treatment, only 2 cases was significantly absorbed of the lesions after 2 months, and all the lesions of the 6 cases absorbed after 6 months anti-TB treatment.ConclusionCT is more valuable in the screen of TB outbreak in school compared with DR. Subclinical cases detected by CT is recommended to take a formal anti-TB treatment.