Though tuberculosis (TB) is an old disease, with cases dating back 5,000 years, it remains a major global health threat. Accurately detecting latent TB infections, when the infection is still dormant and not actively making a person sick, is key to public health efforts to eliminate the disease.<\/p>\n
New research from the University of Georgia is the first population-level study to examine whether the primary diagnostic tool for latent TB, a tuberculin skin test, could misidentify individuals as new cases of latent TB in areas where the disease burden is very high.<\/p>\n
The proper identification of new cases using the tuberculin skin test has implications for who is treated, says Juliet Sekandi, an assistant professor in the Global Health Institute at UGA\u2019s College of Public Health and lead author on the study.<\/p>\n
Sekandi and colleague Chris Whalen were leading a research team gathering survey data in Kampala, Uganda, when they noticed an unusually high rate of reported latent TB, over 50 percent of the population.<\/p>\n
\u201cThat\u2019s what triggered this study,\u201d Sekandi said. Tuberculin skin tests can be susceptible to \u201cboosting,\u201d she explained, which can occur when the test triggers an immune response from past exposure to TB bacteria, rather than recent exposure. That can lead to a false positive.<\/p>\n
\u201cWe don\u2019t want to falsely diagnose latent TB because, by policy, it is supposed to be treated,\u201d said Sekandi. \u201cYou treat for six to nine months, so if you\u2019re going to give somebody treatment for nothing when it\u2019s just a boosted reaction, that\u2019s not good.\u201d<\/p>\n
In addition to protecting the patient from unnecessary side effects, it can be costly to treat people who don\u2019t need it. It\u2019s estimated that one-third of the world\u2019s population have latent TB infections, but treatment resources are limited. Public health programs can\u2019t afford to treat a large number of misidentified patients.<\/p>\n
Researchers recruited volunteers in Kampala, who received an initial skin test. If the test came back negative, the participants were asked to return in two weeks for a second test. Of the 99 participants, only two showed a boosted response, suggesting that their immune systems were triggered by the tuberculin in the first skin test rather than actual TB exposure.<\/p>\n
These findings, says Sekandi, are important to public health prevention programs.<\/p>\n
\u201cWe can be confident we aren\u2019t doing too much harm,\u201d she said. \u201cThe takeaway point here is that in high burden settings like Uganda, most of the people that test positive with a skin test are actual cases of latent TB, not just false positives.\u201d<\/p>\n