It’s not TB but what could it be? Abnormalities on chest X-rays taken during the Kenya National Tuberculosis Prevalence Survey

Abstract BackgroundThe prevalence of diseases other than tuberculosis (TB) detected during chest X-ray (CXR) screening is unknown in sub-Saharan Africa. This represents a missed opportunity for identification and treatment of potentially significant disease. Our aim was to quantify and characterise non-TB abnormalities identified by TB-focused CXR screening during the 2016 Kenya National TB prevalence survey. MethodsWe reviewed a random sample of 1140 adult (≥15 years) CXRs classified as “abnormal, suggestive of TB” or “abnormal other” during field interpretation from the TB Prevalence Survey. Each image was read (blinded to field classification and study radiologist read) by two expert radiologists, with images classified into one of four major anatomical categories and primary radiological diagnosis. A third reader resolved discrepancies. Prevalence and 95% confidence intervals of abnormalities diagnosis were estimated. FindingsCardiomegaly was the most common non-TB abnormality at 259/1123 (23.1%, 95% CI 20.6%-25.6%), while cardiomegaly with features of cardiac failure occurred in 17/1123 (1.5 %, 95% CI 0.9%-2.4%). We also identified chronic pulmonary pathology including suspected chronic obstructive pulmonary disease in 3.2% (95% CI 2.3%-4.4%) and non-specific patterns in 4.6% (95% CI 3.5%-6.0%). Prevalence of active-TB and severe post-TB lung changes was 3.6% (95% CI 2.6%-4.8%) and 1.4% (95% CI 0.8%-2.3%) respectively. InterpretationBased on radiological diagnosis, we identified a wide variety of non-TB diagnoses during population-based TB screening. TB prevalence surveys and active case finding activities using mass CXR offer an opportunity to integrate disease screening efforts. FundingNational Institute for Health Research (IMPALA-grant reference 16/136/35). Evidence before this studyTuberculosis (TB) remains the leading adult infectious killer in the world. The World Health Organization (WHO) recommends the use of chest X-ray (CXR) as a mass screening tool in TB prevalence surveys and active case finding activities to identify patients eligible for bacteriological investigation. Mathematical modelling suggests that an algorithm incorporating a screening CXR to direct subsequent Xpert MTB/RIF testing is the optimal pathway with lowest number needed to test at acceptable programme costs in active case finding mass screening activities. Increased digital X-ray availability, coupled with the development of Computer Aided Detection (CAD) software for identification of TB, could enable widespread use of CXR in screening for TB in areas with limited access to radiologists. In addition, CXR has an advantage of detecting conditions besides TB. However, the prevalence of diseases other than TB identified by CXR during TB mass screening or TB prevalence survey activities is unknown.We systematically searched MEDLINE, CINHAL, Global Health and Google scholar databases from 1940–2019 to identify studies that described the prevalence of non-TB CXR findings during TB prevalence surveys or mass screening activities. The WHO Stop TB Department website and reference lists from relevant reviews and studies were used to supplement the search. The search strategy included MESH terms: “Chest Xray” or “Chest-Xray” or “Chest radiograph” or “Mass screening” or “Mass radiography” AND “Tuberculosis screening” or “Tuberculosis triaging” or “TB screening” or “TB triaging” AND “Non-tuberculous” or “Non-TB pathology” or “other pathology”. Our search yielded a number of studies using CXR screening in prevalence surveys as well as active case finding activities. However, studies describing non-TB pathology during mass radiography were few and mostly in the 20th century. A report in Europe between 1946 and 1948 documented 35% non-TB pathology on mass miniature X-rays. Our search did not identify any evidence pertinent to the sub-Saharan African context.Added value of this studyIn this cross-sectional study, we analysed individual-level participant CXR data from the 2016 Kenya National TB Prevalence Survey. Our aim was to quantify and characterise non-TB abnormalities identified by TB-focused CXR screening during the survey. We hypothesised that non-TB abnormalities requiring further clinical review are highly prevalent and need to be considered when implementing CXR screening for TB. Our study identified multiple non-TB diagnoses. The most prevalent was cardiomegaly at 23.1% (95% CI 20.6%-25.6%). We also identified chronic pulmonary pathology including suspected chronic obstructive pulmonary disease (COPD) and non-specific interstitial patterns. Mediastinal masses, excluding goitres, occurred in 0.8% (95% CI 0.4%-1.5%). TB related abnormalities, which may cause chronic respiratory symptoms, such as severe bronchiectasis and/or destroyed lung were present in 1.4%(95% CI 0.8%-2.3%). Median CAD4TB scores were low for the non-TB abnormalities.Implications of all the available evidenceOur study demonstrated a high prevalence of CXR-identified non-TB abnormalities, including cardiomegaly, chronic pulmonary diseases, post-TB lung disease and non-specific lung diseases. Implementation of CXR TB screening in this context requires detailed health system planning to incorporate provision of care to people with non-TB abnormalities. This could include incorporation of additional tests such as blood pressure monitoring and spirometry as part of community TB screening interventions.