Ocena stopnia zakażenia prątkiem gruźlicy (utajonej infekcji gruźliczej) przy pomocy testu QuantiFERON-GIT (QFT-GIT) w wybranych grupach ryzyka w populacji Krakowa

*Katarzyna Kruczak¹, Wojciech Skucha², Mariusz Duplaga¹, Marek Sanak¹, Ewa Niżankowska-Mogilnicka¹

Streszczenie
Introduction:Poland is characterized by high prevalence of tuberculosis (22.7/100 000 in 2007). Diagnostics of the infection caused by M. tbc (latent tuberculosis infection) is difficult due to obligatory multiple BCG vaccination for many years and low specificity of tuberculin skin test. Specific risk groups are particularly endangered with infection.
Aim: The objective of the study was assessment of the prevalence of latent tuberculosis infection in risk groups including homeless as well as persons being so called „close contacts” or „transient contacts” for patient suffering from tuberculosis.
Material and methods: QFT-GIT test was performed in 397 subjects: 134 homeless persons, 121 persons remaining „close contacts” and 142 persons remaining „transient contacts” within the period from June 2007 to May 2008. Skin tuberculin test was carried out in 89, 112 and 122 subjects respectively belonging to appropriate groups. All subjects answered to specially prepared questionnaire for the study. In each group, the correlation between the results of QFT-GIT test and age, results of skin tuberculin tests (serum level of interferon-gamma and diameter of skin reaction to tuberculin were considered). The threshold level for positive tuberculin skin test for good correlation with QFT-GIT test results was also analysed.
Results: The authors observed high level of M. tbc latent infection in relevant studied groups: 38%, 26% and 18% respectively. The correlations were significantly positive between QFT-GIT test results and age of subjects included in the study, between QFT-GIT test results and skin tuberculin tests as well as between serum levels of interferon-gamma and diameter of skin tuberculin tests. Concordance levels between QFT-GIT test and skin tuberculin test (10 mm skin reaction interpreted as positive) were: 78.5%, 68.2% and 60.3% respectively while kappa coefficients were: 0.38, 0.37 and 0.17 respectively.
Conclusions: Prevalence of M. tbc latent infection in risk groups for infection remains high. Threshold of skin tuberculin test for good correlation with QFT-GIT test results is lower than assumed previously. Skin tuberculin test is characterized by lower diagnostic value in Polish population vaccinated with BCG.

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