Prevalence of Latent Infection with Mycobacterium Tuberculosis in Mazowieckie Province Using Interferon Gamma Release Assay after Stimulation with Specific Antigens ESAT-6 and CFP-10

Introduction: Over 8000 cases of tuberculosis (TB) are diagnosed annually in Poland. People infected with Mycobacterium tuberculosis (MTB) have a risk of active disease of around 10% during their whole life, and the risk is highest in the first two years after infection. Recognizing infection before TB disease development enables prophylaxis against its activation and ceases transmission of infection. Knowledge about the proportion of infected people in the population is crucial to predict the number of new cases of active disease. Materials and methods: The prevalence of latent TB infection (LTBI) was tested in 700 healthy adult inhabitants of the Mazowieckie province in different age groups, using both tuberculin skin test (TST) and interferon gamma release assay (IGRA). Commercial test QuantiFERON^®-TB-Gold In Tube (QFT) was used. All participants were mandatorily BCG vaccinated according to the Polish vaccination schedule. Results: Twenty-three per cent of participants tested positively for QFT, which was significantly less than for TST (50.3%). The prevalence of positive QFT results increased with age, as well as the incidence of TB in Poland. Positive QFT was most frequent in the oldest age group (48.8%) and rarest in the youngest (7.1%). Conversely, positive TST occurred more often in younger participants (45%), who rarely suffer from TB. Among people over 60, with the highest TB incidence rate, only 33.8% tested positively with TST. Concordance between both tests was low, with a kappa value of 0.198. The prevalence of LTBI defined as positive QFT among health care workers (HCW) was significantly higher than among other participants (32.2% v. 20.4%, p < 0.01). Conclusions: LTBI was diagnosed in 23.3% of the tested population of the Mazowieckie province. QFT is a better tool for diagnosing LTBI as it shows a positive correlation with age (as the incidence of TB disease does). Concordance between both tests is low. The prevalence of LTBI in HCW is higher than in other participants.