Researchers from the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing have found tuberculin skin testing may be overestimating the prevalence of latent tuberculosis in China.
They suggest that Bacille Calmette-Guérin (BCG) vaccination and age might affect the performance of the tuberculin skin test (TST) compared with QuantiFERON (interferon-gamma release assay, Qiagen).
“Our results provide valuable insight into the prevalence of latent tuberculosis infection in countries with a high burden, but medium incidence, of tuberculosis where BCG vaccination is routinely given,” the researchers wrote in Lancet Infectious Diseases. “Specifically for China, our results suggest that the rate of latent infection is not as high as previously described. This finding suggests that community-based preventive interventions to control disease development from latent tuberculosis might be practical for individuals at high risk for developing active diseases.”
From July 2013 through September 2013, the researchers conducted a baseline survey of a population-based, multicenter prospective cohort study of residents aged 5 years and older. They identified 23,483 eligible participants from a door-to-door survey, and screened participants for active TB and a history of TB. They then tested the participants for latent infection using a TST and an interferon-gamma release assay.
Ninety percent of participants completed the baseline survey. The rate of TST positivity, measured as an induration of 10 mm or more, ranged from 15% to 42% at the four study sites. The rate of positivity, according to interferon-gamma release assay, ranged from 13% to 20%. The rates of positivity for both tests were lowest among participants aged younger than 20 years and increased with age (P < .0001).
There was an 81% concordance between the tests, with a kappa coefficient of 0.485 (95% CI, 0.471-0.498). TST positivity only was associated with BCG vaccination, being aged 60 years and older and male sex. Interferon-gamma release assay positivity alone was associated with male sex and being aged 60 years and older.
“The effect of age and BCG vaccination on the tuberculin skin test might explain the discordance between these two methods,” the researchers wrote. “Therefore, our results suggest that the presently estimated rates of latent tuberculosis in endemic regions of China have probably been overestimated by the tuberculin skin test compared with interferon-gamma release assays.”