Setting: Sweden under transition from high to low tuberculosis (TB) incidence from 1920 to 2009.
Objective: To correlate estimates of TB infection in birth cohorts with the longitudinal incidence of active TB to assess the long-term risk and time pattern of reactivated TB.
Design: Time trend analysis on TB incidence using age-cohort modelling.
Results: The overall TB incidence decreased from 700 per 100,000 population in 1920 to 1.4 in 2009 in the Sweden-born population. The estimated disease rate (number of cases divided by the estimated number of infected in 1967), for each birth cohort between 1920 and 1940, was stable on a level between 9.8% and 10.7%. The reactivation rate of latent TB infection (LTBI) was 2% after 1967, when indigenous transmission had disappeared.
Conclusion: Although approximately 10% of persons with LTBI developed active TB, the majority of cases occurred shortly after infection, and the rates of reactivation declined over time. This indicates extensive spontaneous clearance of LTBI.