Birth cohort effect on latent tuberculosis infection prevalence, United States

Background: Latent tuberculosis infection (LTBI) prevalence in the United States decreased approximately 60% in the three decades between the 1971-1972 and 1999-2000 National Health and Nutrition Examination Survey (NHANES) surveys. We examined the effects of birth cohort on LTBI prevalence over time. Methods: Using weighted data analysis software to account for NHANES survey design, we calculated the difference in LTBI prevalence between 1971-1972 and 1999-2000 for birth cohorts corresponding to 5-year intervals (1912-1916, 1917-1921, 1922-1926, 1927-1931, 1932-1936, 1937-1941, 1942-1946). Results: LTBI prevalence was significantly lower in 1999-2000 compared to 1971-1972 for cohorts born in 1926 or earlier (19% versus 5%), but not for cohorts born 1927-1946 (9% versus 7%). Adjustment for cohort restriction and foreign-birth did not qualitatively change the results. Conclusions: Although older age groups have higher rates of TB infection than younger groups, nationally representative U. S. survey data suggest that observed LTBI prevalence in older people represents an underestimate of infection, because of the birth cohort effect and waning immunologic reactivity.