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Published on: July 11, 2015
Time interval to conversion of interferon-gamma release assay after exposure to tuberculosis
1Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Armed Forces Capital Hospital, Lung Institute, Seoul National University College of Medicine, 101 Daehangno, Jongno-gu, Seoul, 110-744, Republic of Korea.
Insights
Repeating interferon-γ release assays (IGRA) for tuberculosis contacts with negative initial results is crucial. IGRA conversion typically occurs 4-7 weeks post-exposure, but can be delayed up to 22 weeks.
Area of Science:
- Infectious Diseases
- Immunology
- Public Health
Background:
- Tuberculosis (TB) transmission necessitates effective contact tracing and monitoring.
- The optimal timing for repeat Interferon-Gamma Release Assays (IGRA) in initially negative TB contacts remains undefined.
- Active pulmonary tuberculosis outbreaks require timely identification and management of exposed individuals.
Purpose of the Study:
- To determine the appropriate interval for repeating IGRA in TB contacts with negative initial results.
- To evaluate the timeline of IGRA conversion following exposure to active pulmonary TB during an outbreak.
- To inform latent TB infection management strategies based on IGRA conversion patterns.
Main Methods:
- A cohort of 32 military contacts exposed to active pulmonary TB was studied.
- Tuberculin skin test (TST) and QuantiFERON® TB-Gold In-Tube (QFT-GIT) assays were performed initially.
- QFT-GIT was repeated serially (2, 4, 8, 14, 18, 30 weeks) for initially negative contacts until conversion or study end.
Main Results:
- Initially, 63.0% (17/27) of contacts had positive QFT-GIT results, and 77.8% (21/27) had positive TST results.
- Among 10 initially QFT-GIT negative contacts, 9 converted: 3 at 2 weeks, 3 at 4 weeks, and 3 at 14 weeks.
- IGRA conversion typically occurred 4-7 weeks after exposure, with a late conversion observed 14-22 weeks post-exposure.
Conclusions:
- Serial IGRA testing is valuable for detecting latent TB infection in initially negative contacts.
- IGRA conversion after TB exposure can occur up to 22 weeks post-exposure, necessitating extended monitoring.
- Findings support a testing interval of at least 14 weeks for IGRA-negative TB contacts to capture conversions.
Abstract:
The proper interval for repeating an interferon-γ release assay (IGRA) among tuberculosis contacts with initially negative results is unknown. The interval for IGRA conversion after exposure to patients with active pulmonary tuberculosis in an outbreak setting was evaluated. In a platoon of 32 soldiers, four active pulmonary tuberculosis patients, in addition to one index patient, were diagnosed during a contact investigation. For the other 27 contacts, a tuberculin skin test (TST) and QuantiFERON® TB-Gold In-Tube (QFT-GIT) assay were performed. For soldiers with a negative result on the initial QFT-GIT assay, the test was repeated at 2, 4, 8, 14, 18 and 30 weeks until positive conversion occurred. When conversion was identified, the subject was treated for latent tuberculosis infection. Initially, 17 (63.0%) soldiers gave positive QFT-GIT results, whereas 21 (77.8%) showed positive TST results. Among 10 participants with initially negative QFT-GIT results, three showed conversion at 2 weeks, three at 4 weeks and three at 14 weeks. Conversion did not occur during the 30-week observation period in one contact. Based on the tuberculosis exposure time-points among the contacts, IGRA conversion generally occurred 4-7 weeks after exposure, although it could occur as late as 14-22 weeks after exposure.
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