Background. Correct identification of individuals with latent tuberculosis infection (LTBI) is a crucial element of the elimination strategy, allowing their adequate treatment. In addition to tuberculin skin test (TST), the Quantiferon test (QFT, based on whole blood γ-interferon release) had been recently proposed. Aim of the study is to compare this test to TST for identification of LTBI in a non-selected population, in order to verify their value in identifying truly infected individuals (entitled to receive preventive chemotherapy), and to exclude from treatment those having a positive TST for other reasons (e.g. after BCG vaccination). Methods. 136 consecutive persons (78 males, mean age 34±9 years) referred to the clinic for TST were recruited (78 born in low - or middle - income countries). Based on their history, the cases were divided into 4 groups: 1) recently traced contacts of whom 18 TST negative and 28 TST positive; 2) 22 screening subjects, all TST negative; 3) BCG vaccinated subjects (14); and 4) 54 subjects already undergoing treatment of LTBI for exposure to TB. Results. The overall agreement between TST and QFT was 72% (64% in TST positive and 88.4% in TST negative subjects). The proportion of TST positive/QFT negative BCG vaccinated individuals was 23.1%. The K coefficient was 0.474 in recently traced contacts, 0.366 in BCG vaccinated individuals and 0.451 overall. Conclusions. The study results suggest that agreement between TST and QFT is lower in TST positive than in negative subjects, being lower in individuals treated for LTBI. Quantiferon does not seem to have brought significant improvement in the diagnosis of LTBI.
The main goals of our study were to evaluate: 1) the annual risk of tuberculosis infection (ARTI) and its annual decrease in Uganda; 2) the expected incidence of new tuberculosis cases and the notification rate; and 3) the role of incentives given to children tested in increasing compliance with the survey procedures. The methodology is based on performing the standard World Health Organization (WHO) tuberculin test on children of the same age groups at intervals of 10-15 yrs, identifying infected persons by induration distribution analysis, and converting the prevalence rates detected into risk rates according to the ARTI model. Two thousand six hundred and twenty one school children aged 10 yrs old and bacilli Calmette-Guerin (BCG) nonvaccinated, in six study areas, were injected with two tuberculin units (TU) of purified protein derivative (PPD) RT 23 Copenhagen. The detected prevalence was 14 +/- 1.4% (prevalence +/- 95% confidence interval (95% CI)) and the ARTI value 1.2 +/- 0.9%, with an estimated annual decrease of 0.83% from 1958 to 1970 and 2.9% in the 1970-1987 period. The estimated expected incidence of new cases in Uganda was 59 smear positive and 75 smear negative/extrapulmonary cases per 100,000 population in 1987, and 53 and 65, respectively, in 1990, with an overall 68% notification coverage. No significant improvement in children returning for reading was observed in the group receiving incentives. We conclude that the average decrease (2.9%) probably represents the natural decline of tuberculosis in Uganda. The coverage appears encouraging, although the ARTI detected could be underestimated, since the existing ARTI model was developed and validated before the human immunodeficiency virus (HIV) era.(ABSTRACT TRUNCATED AT 250 WORDS)
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