Use of the T-SPOT.TB assay to screen latent tuberculosis infection among the TB contacts in Shanghai, China

Background: There is limited information on the prevalence of latent tuberculosis infection (LTBI) and the risk factors among contacts of pulmonary TB, which might contribute significantly to TB burden and therefore become the major concern for TB control in Shanghai, China. Methods: A total of 45 diagnosed TB patients from each of 7 Shanghai districts were chosen and approximately 3 contacts per case were randomly selected. A structured questionnaire was used to acquire socio-demographic information and to assess the degree of exposure to index cases. LTBI screening was performed by T-SPOT.TB assay. Results: Of 969 enrolled contacts, 39% were men, average age was 45 ± 19.1 years, and 76.3% were household contacts. LTBI was identified in 29.6% of subjects. Those contacting smear-positive TB patients were 2.24 times (95%CI, 1.586-3.162) more likely to develop LTBI than those otherwise; household contact significantly increased the likelihood of LTBI by 1.52 times (95%CI, 1.061-2.180). Furthermore, among household contacts, the risk of LTBI was higher in spouses and first-degree relatives and increased with age and contact duration. Conclusions: A high prevalence of LTBI was observed among the TB contacts in Shanghai, highlighting the need of intervention among the household contacts and those contacting smear-positive TB patients.