Latent tuberculosis infection among close contacts of non-residential pulmonary tuberculosis patients in Shanghai, China

Background: Under the fast urbanization, Shanghai is hosting more and more domestic rural-to-urban migrants who do not have a certified local residence. Tuberculosis is more prevalent in rural population in China. In 2014, non-residential population has accounted for 42.9% of new pulmonary tuberculosis (PTB) patients in Shanghai. Close contacts of non-residential patients are at high risk of latent tuberculosis infection (LTBI). This study aimed to understand the prevalence of LTBI in close contacts of non-residential PTB patients, and to identify the risk factors associated with LTBI in Shanghai. Methods & Materials: A cross-sectional study was conducted among close contacts of non-residential PTB patients diagnosed in 2013-2014 in 4 districts of Shanghai. T-SPOT.TB was applied to detect the LTBI among contacts, together with a questionnaire for collecting information on demographics, socio-economic status, history of Bacille Calmette-Guérin (BCG) vaccination, symptoms of TB and details of contacting. The status of LTBI was defined as T-SPOT.TB positive plus no TB symptoms and a normal lung image by chest X-ray. Results: In this study, 460 close contacts were self-reported by 226 registered PTB patients. Of these contacts, 43.0% were male and 58.0% were BCG vaccinated. Overall, 83 contacts had positive T-SPOT.TB results without TB symptoms, which presented an 18.0% (95%CI: 14.5%∼21.6%) prevalence of LTBI. The prevalence of LTBI increased with age (X2liner trend=3.910, p=0.048), and exposure duration to PTB patients (X2liner trend=6.401, p=0.011). Stratified analysis by age (0-19, 20-39, 40-59, and ≥60 years) indicated that the association between LTBI prevalence and exposure duration was statistically significant at the age of 20-39 years (X2liner trend=4.947, p=0.026). Multivariate analysis showed that household contact significantly increased the risk of LTBI (aOR=9.030, 95%CI: 2.568-31.756); and contacts of PTB patients having cough (aOR=2.541, 95%CI: 1.258-5.133) and cavities in lung (aOR=1.698, 95%CI: 1.008-2.860) were more likely to be LTBI than those otherwise. Conclusion: Close contacts of non-residential PTB patients had a relatively high LTBI prevalence. Intervention for infection control among PTB close contacts should be concerned in the policy development for ending TB in 2035 in Shanghai.