Tuberculosis infection is not life-long in most people: Study

A recent study challenged the earlier belief that tuberculous infection stays forever and that it could come back at any point and cause the disease again.

Based on a review of clinical studies, researchers from the Perelman School of Medicine at the University of Pennsylvania and colleagues show that people who test positive with immunologic TB skin or blood tests rarely develop TB.

They suggest it's because the infecting organism, Mycobacterium tuberculosis, is likely dead, wiped out naturally by people's immune systems.

Despite that, these people retain an immunological memory to the disease, which the authors said likely explained why standard TB tests show a positive result since those tests look for an immune response and not live bacteria.

The study was published this week in the journal -- BMJ.

The findings upend commonly held beliefs, as well as approaches to care and research around the world, for the two billion people who test positive for TB and are thought to be persistently infected and at risk for active disease.

"The National Institutes of Health and other non-profit organisations spend millions of dollars on studies of the latent state because of the assumption that TB infection is life-long, held in check by the immune system," said co-author Paul H. Edelstein, MD, an emeritus professor of Pathology and Laboratory Medicine at Penn.

"However, based on our analysis, we believe that it is rarely life-long, and in 90 per cent or more of infected people, there is no possibility of TB development even with severe immunosuppression," added Edelstein.

Additional co-authors on the study include Marcel A. Behr, MD, a professor of Medicine at McGill University, and Lalita Ramakrishnan, MD, a professor of Immunology and Infectious Diseases at the University of Cambridge.

In their review, the team pointed to several previous studies to demonstrate the natural history of TB immunoreactivity in people given preventive treatment, and of active TB in immunoreactive people with various forms of severe immunosuppression, like patients with HIV and those who have received an organ transplant.

"TB immunoreactivity is not a marker for the presence of continued TB infection," Edelstein's team wrote. "Rather, it serves as a sign of having been infected with TB at some point."

The researchers believe future resources should focus on developing tests that can better identify infected people who are not symptomatic. Currently, there are no specific tests for these patients.

They also believe that detecting and treating people with active TB should be a high priority, as well as providing TB preventive therapy for those around them.