Screening for pulmonary tuberculosis in a Tanzanian prison and computer-aided interpretation of chest X-rays

Tuberculosis (TB) is responsible for at least 1.5 million deaths annually despite the existence of effective treatment. Data from national TB programmes report 6 million new cases per year, but this figure is probably still 3 million short of the actual number, as many cases are not properly diagnosed or reported.1 Tanzania is one of 22 high burden countries, with a TB prevalence of 295 per 100 000 population, as shown in the latest national TB prevalence survey.2 The problem is accentuated in prisons, where the incidence and prevalence of TB are many times higher than in the general population.3,4 In particular, prisons in sub-Saharan Africa have a high turnover of detainees, while factors such as overcrowding, poor nutrition and illegal drug use are likely causes for the high TB prevalence of up to 5%.5,6 Previous studies in prisons in Tanzania have shown a high proportion of new cases and smear-positive TB.7 Preliminary data from a study in Mbeya, Tanzania, estimate TB prevalence at 0.88–4.38% in Tanzanian prisons.8 Early detection is particularly important for the effective prevention and control of TB in prisons.9 The World Health Organization recommends systematic screening of prisoners in countries with high TB prevalence, proposing chest X-ray (CXR) as an initial examination.10 Radiography would detect more active TB cases than the clinical questionnaires that are currently used to discover TB cases in African prisons.3 Unfortunately, the diagnostic accuracy of CXRs for the detection of active pulmonary TB (PTB) is highly dependent on the reader,11,12 and health personnel with TB-specific radiology training are scarce in sub-Saharan Africa, especially in the health facilities of penitentiary institutions. Digital X-ray equipment and the automated reading of CXRs with computer-aided detection (CAD) have the potential to expand the use of radiology in the diagnosis of PTB and to increase its objectivity. Previous studies have established good diagnostic performance of the software Computer Aided Detection for Tuberculosis (CAD4TB, Delft Imaging Systems, Veenendaal, The Netherlands) in a patient population seeking care for TB-related symptoms.13–15 In this study, we examined the potential benefits of CAD4TB when screening a prison population for active PTB and assessed the diagnostic accuracy of CAD4TB in a predominantly asymptomatic prison population. In addition, we recorded parameters to assess the operational feasibility of such screening. All data were collected during ongoing TB screening of the entire prison population.