Latent TB curbs risk of active disease
Latent tuberculosis appears to protect people from developing active TB if they're reinfected, Boston-based researchers report.
"In this study, we were attempting to answer the very old and vexing question regarding the extent to which individuals who are infected with tuberculosis, but haven't developed the disease, are protected from developing disease following a second exposure," Dr. Jason R. Andrews of Massachusetts General Hospital told Reuters Health by email.
The answer wasn't sitting in today's modern electronic databases.
"To answer this question," Dr. Andrews said, "we looked back at historical cohorts of doctors, nurses and students from the 1920s to the 1950s, who worked in an era where tuberculosis was widespread in hospitals."
In fact, he and his colleagues note in their report, the high rates of infection in those days, and lack of drugs for treating latent diseases, allowed for observational studies that could not be performed today.
The researchers identified 18 publications reporting tuberculosis incidence among 23 paired cohorts of almost 20,000 people with and without latent infection.
They reported online January 19th in Clinical Infectious Diseases that the weighted mean adjusted incidence rate of tuberculosis per 1,000 person-years was 13.5 in the latent group and 60.1 in the initially uninfected group.
This gave an incidence rate ratio of 0.21 -- lower than most previous estimates.
"We found that the risk of tuberculosis following tuberculosis exposure was 79% lower in individuals who had been previously infected (compared with those who had not been previously infected)," Dr. Andrews said.
"Healthcare providers and individuals living in countries or settings with a high burden of tuberculosis often are exposed to tuberculosis multiple times in their lives," he added. "If the risk of tuberculosis isn't high upon second exposure, this could have important implications for treating latent tuberculosis and managing outbreaks."
"It also could give us some insight into how effective a vaccine that replicates natural immune responses could be," he said.
An editorial by Drs Andrew A. Vernon and M. Elsa Villarino of the Centers for Disease Control and Prevention, Atlanta, Georgia, characterizes the study as a creative endeavor but notes, "A broad range of research is still needed in our efforts to understand this ancient pathogen and to develop effective measures to prevent its continued toll on humankind."
SOURCE: http://bit.ly/wyIYwC
Clin Infect Dis 2012.
