The burden of subclinical TB in Nigeria

SETTING This study is a retrospective review of a large-scale systematic TB screening project conducted in six states of Nigeria. OBJECTIVE To determine the magnitude and characteristics of subclinical TB and the relative contributions of bacteriological versus clinical diagnosis in its identification in Nigeria. DESIGN Data were retrospectively analysed from six states of Nigeria, where parallel screening with any TB symptoms and chest X-ray (CXR) with artificial intelligence (AI) was used for active case finding. Diagnosis of TB among presumptive was confirmed using either bacteriological tests or clinical review of CXR. RESULTS Out of 8,516 presumptive identified during the project, 172 (2.0%) had no TB symptoms (males: 73.8%, females: 26.2%). The overall prevalence of TB among all presumptive was 21.9% (n = 1,867), including 62 (3.3%) subclinical TB and 1,805 (97.3%) active TB cases. The proportion of clinical diagnosis using CXR was significantly higher in the subclinical TB group than in the active TB group (79.0% vs. 63.5%; P = 0.012, OR = 2.2, 95% CI 1.17-4.03). CONCLUSION Subclinical TB contributed 3.3% of the large TB burden in this study (22 per 100 presumptive). These cases would have been missed if only symptom-based TB screening had been employed.