Interferon-γ and Immunoglobulins in Latent Tuberculosis Infection

Background and AimsThe aim of the present study was to investigate the occupational risk of tuberculosis in health care workers (HCW) at a children's hospital in a middle-income country with an intermediate prevalence of tuberculosis and compulsory bacille Calmette-Guérin vaccination and to assess the association of latent tuberculosis infection (LTBI) with the concentration of immunoglobulins (IgG, IgA, IgM), C-reactive protein and hematological changes.MethodsFifty four HCW were divided into groups according to their exposure to tuberculous patients and interferon (IFN-γ) findings. IFN-γ determination and tuberculin skin test (RT23) were performed in parallel.ResultsPositive IFN-γ results were recorded in 31% of study HCW. Higher exposure to tuberculous patients did not lead to a statistically significant increase in the rate of positive IFN-γ findings but did increase the number of hyperreactors. HCW with positive IFN-γ findings were 5 years older than IFN-γ negative subjects. The median IgA concentration was 29% higher (p = 0.0233) in IFN-γ positive subjects (2.44 g/L) as compared with IFN-γ negative subjects (1.89 g/L).ConclusionsStudy results showed the prevalence of LTBI in HCW at a children's hospital to be comparable to the prevalence recorded in the general population. IFN-γ proved to be a more reliable test to determine LTBI in a population of bacille Calmette-Guérin-vaccinated HCW. The new diagnostic approach will hopefully contribute to more rational use of x-rays and prevent unnecessary administration of chemoprophylaxis. The higher concentration of IgA in IFN-γ-positive HCW pointed to the possible protective role of IgA antibodies in LTBI.