Interferon-γ and Immunoglobulins in Latent Tuberculosis Infection

Background and Aims. The 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-Guerin 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. Methods. Fifty four HCW were divided into groups according to their exposure to tuberculous patients and interferon (IFN-gamma) findings. IFN-gamma determination and tuberculin skin test (RT23) were performed in parallel. Results. Positive IFN-gamma 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-gamma findings but did increase the number of hyperreactors. HCW with positive IFN-gamma findings were 5 years older than IFN-gamma negative subjects. The median IgA concentration was 29% higher (p = 0.0233) in IFN-gamma positive subjects (2.44 g/L) as compared with IFN-gamma negative subjects (1.89 g/L). Conclusions. Study 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-gamma proved to be a snore reliable test to determine LTBI in a population of bacille Calmette-Guerin-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-gamma-positive HCW pointed to the possible protective role of IgA antibodies in LTBI. (c) 2009 IMSS. Published by Elsevier Inc.