Screening for Mycobacterium tuberculosis using an interferon-gamma release assay

Area of Science:

• Public Health
• Infectious Disease Epidemiology
• Clinical Diagnostics

Background:

• Centers for Disease Control and Prevention recommend analyzing Mycobacterium tuberculosis infection screening using interferon-gamma release assays (IGRAs).
• IGRAs are increasingly utilized for tuberculosis (TB) screening.

Purpose of the Study:

• Characterize IGRA test requests at the first Washington State laboratory offering the assay.
• Document the implementation process of IGRA testing in a public health setting.

Main Methods:

• Retrospective record review of 4422 IGRA requests from 4218 unique subjects (2008-2009).
• Analysis included IGRA results, request source, reasons for testing, demographics, risk factors, and prior TB exposure.
• Examined Tuberculin Skin Test (TST) induration sizes in relation to IGRA results.

Main Results:

• Most IGRA requests (96%) originated from public health clinics, hospitals, private practitioners, and Indian Health Centers.
• Community and migrant health centers exhibited the highest positive IGRA rates (28%).
• Approximately 50% of requests were for employment or high-risk surveillance.

Conclusions:

• Public and private entities utilize IGRAs for surveillance of various populations, including those employed, at high risk, or foreign-born.
• Significant variation in TST induration was observed for individuals with indeterminate IGRA results.
• The program's implementation process can serve as a model for other IGRA analysis reviews.