European Respiratory Society

Serial testing using interferon-γ release assays in nursing students in India

Alice Zwerling, Madhukar Pai, Joy Sarojini Michael, Devasahayam J. Christopher

To the Editor:

We have previously shown that Indian healthcare workers have higher prevalence of latent tuberculosis infection (LTBI) and are at increased risk for new infection [1]–[4]. Interferon-γ release assays (IGRAs) have been introduced as an alternative to the tuberculin skin test (TST) for diagnosing LTBI in healthcare workers and other high-risk groups. They have logistical advantages over the TST and will not cross-react with the bacille Calmette Guérin vaccine. IGRAs are now being widely used for screening healthcare workers [5], yet recent reports indicate that switching from TST to IGRAs for the serial testing of healthcare workers may result in increased rates of test conversions and reversions [3], [6]–[8]. Most of these studies are from low tuberculosis (TB) incidence settings, with limited opportunity for nosocomial TB exposure; as a result, the increased conversion rates are considered false-positive test conversions, making it difficult for clinicians to interpret IGRA test conversions in these settings [9]. It remains unclear whether IGRA conversions are associated with TB exposure in high TB incidence settings where unprotected exposure to infectious TB patients is more common among healthcare workers.

To evaluate whether IGRA conversions may represent new cases of LTBI, in a high TB incidence setting, in the absence of a gold standard for LTBI, we employed TB exposure as a proxy measure. We established a cohort of nursing students who underwent IGRA testing annually for 3 years at a tertiary level hospital in southern India [1]. Annual rates of conversions and reversions were estimated in this cohort. A relationship between occupational TB exposure and change in continuous interferon-γ (IFN-γ) levels were …

Log in through your institution