Risk of developing tuberculosis in T-cell spot test of tuberculosis infection positive close contacts of tuberculosis patients in Shanghai: a prospective observational study / 中华传染病杂志

ABSTRACT

Objective:To investigate the risk and temporal characteristics of tuberculosis (TB) in persons with latent tuberculosis infection (LTBI) among close contacts of TB patients in Shanghai.Methods:This was a prospective observational study, the study subjects were the close contacts of TB patients who tested positive for Mycobacterium tuberculosis infection by T-cell spot test of tuberculosis infection (T-SPOT.TB) among the registered population in seven districts of Shanghai from 2009 to 2010. Questionnaire interview was applied to investigate the basic information and contact history.The LTBI cases during nine consecutive years were identified through the TB registration and reporting system.Cumulative incidence rate and incidence density of TB in tuberculosis-infected close contacts were estimated. Chi-square test was used to compare the incidence rate among different sex and age groups. Results:In total, 376 pulmonary TB patients and their 982 close contacts were enrolled in the baseline survey from 2009 to 2010. Of them, 287 close contacts were tested positive for Mycobacterium tuberculosis infection by T-SPOT.TB.The median age of persons with LTBI at the time of survey was 54 years old, and 36.6%(105/287) were male. By the end of December 2019, five new TB cases were detected among the 287 close contacts with LTBI. The two-year and five-year cumulative incidence were 0.35% and 1.05%, respectively. The nine-year cumulative incidence was 1.74%(95% confidence interval 0.57%-4.02%). The median duration for TB occurrence was 3.67 years. The incidence density of TB was 1.875/1 000 person-years with a total of 2 666.75 observation person-years. There were no significant differences in the nine-year cumulative incidence of TB among close contacts with LTBI by age and sex ( χ2=0.600, <0.001, respectively, both P>0.05). Conclusion:The occurrence of TB among close contacts with LTBI is concentrated in the first five years after TB contact.