Relevance of serial interferon-γ release assays in health-care workers.

We read with interest the study by Park et al 1 (see page 1461) in which they nicely evaluated serial interferong (IFNg )-release assays (IGRAs) in the diagnosis of Mycobacterium tuberculosis (MTB) infection in health-care workers. Health-care workers, although at high risk for MTB infection, are generally less likely to develop active or severe TB. Considering unexplained fl uctuations in IFNg levels, along with the high risk of conversions due to false positives in serial assays, 2 conducting monthly IGRAs in health-care workers may give varied values that may not be of clinical use. Rather, it would be useful for the readers if the authors could provide follow-up data on the proportion of patients who received a diagnosis of MTB (IGRA-positive) who actually progressed to active TB. Retrospective evaluation of serial IFNg levels of such patients could provide a strong basis for formulating guidelines, incorporating their role in the management of latent and active TB. It has been shown that circulating IFNg levels decrease with isoniazid and rifampicin chemoprophylaxis. 3 However, the reasons for reversion of IGRAs in a subset of patients in the study was not discussed. It would be helpful if the authors could discuss the causes of such individual variations in IFNg response, as well as differentiate nonspecifi c variations from those associated with new or resolving infection.