[Risk of tubercular infection among schoolchildren with high BCG coverage].
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Abstract:
Mycobacterium tuberculosis infections may be difficult to detect by the tuberculin test in populations where nonspecific tuberculin sensitivity (induced by BCG and "atypical" mycobacteria) is frequent. In those populations, the rate of M. tuberculosis infection can be determined by comparing the levels of sensitivity before and after BCG vaccination, and classifying as infected those who do not show increased sensitivity in the post-vaccination test. To test this method on a BCG-vaccinated population, a survey was carried out in a sample of 1,721 schoolchildren 6 to 10 years of age, from a suburban area of the city of Rio de Janeiro, where BCG vaccination had been carried out on a large scale. The results suggest that the method is valid for BCG-vaccinated populations, although its accuracy may be affected by the intrinsic variability of tuberculin tests and BCG vaccination, by the action of infections with non-tuberculous mycobacteria, and by low infection rates. The tuberculous infection rate found in the sample group (4.13%) was compared with the results of a tuberculin survey carried out in the same area in 1970, and the incidence of infection was found to be decreasing by 7.68% annually. The annual risk of tuberculous infection for 1986 was 0.36 or 0.51%, depending on the mathematical model used for the calculation. These figures are smaller than the official estimates derived from the incidence rates of notified cases or from surveys made before intradermal vaccination was adopted. This may be due to methodological error, inaccuracies of notification data, association between age and risk of infection and/or peculiarities of the surveyed area.Keywords:
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Groups of BCG-vaccinated guinea pigs were given a single Mantoux skin test 4 to 69 weeks after vaccination. The skin reactions tended to develop more slowly the longer the interval since BCG vaccination. Relatively quickly developing tuberculin skin reactions may be characteristic not only for repeated testing, but also for skin tests taken shortly after BCG vaccination.
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Various populations at high risk for tuberculosis (TB) infection and with high bacille Calmette-Guérin (BCG) vaccination coverage in eastern Taiwan.To investigate the usefulness of the tuberculin skin test (TST) to diagnose TB in BCG-vaccinated populations.Cross-sectional survey.TST reaction size was recorded for 444 individuals ranging in age from 8 months to 99 years, of whom 94.3% had scars to suggest previous BCG vaccination. The TST-positive (> or =10 mm) rate was increased in all comparisons of higher to lower TB risk, including household contacts (relative risk [RR] 3.52, P < 0.0001) and intermediate risk residents (RR 2.30, P = 0.030) compared to a lower risk control group. Advancing age was generally associated with increases in the TST-positive rate. Gender or the number of BCG vaccinations had no relation to the TST-positive rate.The results of this survey suggest that in eastern Taiwan a positive TST represents either active or latent TB infection rather than past BCG vaccination. Therefore, high BCG vaccination coverage in this region does not appear to limit the usefulness of the TST as a tool for diagnosing TB.
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A controlled trial of BCG vaccination was conducted in 1950 in Muscogee County, Ga., and Russell County, Ala. The study population consisted of 64,136 volunteers over the age of 5 years who had satisfactory skin tests with 5 tuberculin units of purified protein derivative and whose chest photofluorograms were considered by two readers to show no significant pulmonary abnormalities. Approximately half of the nonreactors to tuberculin were vaccinated with the Tice strain of BCG by a multiple-puncture method. During a 20-year period of follow-up, 207 cases of tuberculosis were identified among the persons who had been tuberculin reactors in 1950, 36 cases were identified among the controls, and 32 cases were identified among the vaccinees. The average annual case rates per 100,000 were 47.0 for reactors, 13.4 for controls, and 12.6 for vaccinees.
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Bacillus Calmette Guerin (BCG) vaccination used in the prevention of tuberculosis may cause problems in interpreting the tuberculin skin test (TST), which is commonly used in the diagnosis of infection. A limited number of studies have been undertaken to investigate how length of time after BCG vaccination affects TST results. TST induration values of unvaccinated children were compared with those of children vaccinated once in order to determine the changes in TST responses after BCG vaccination. Mantoux TSTs were administered to 1145 children aged 1–6 y and induration was measured at 72 h. BCG scar status and average TST induration diameters were identified for each age group. Conclusion: Average TST induration in vaccinated children is significantly higher than that in unvaccinated children, and in the vaccinated group there is no statistically significant difference between induration values in the different age groups. BCG vaccination at the age of 0–2 mo affects TST for a long period and this condition does not change until 6 y of age.
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During the period 1949-51 a controlled trial of BCG vaccination was initiated among a study population of 191827 children in Puerto Rico. There were 82269 children who were classified as reactors to 10 Tuberculin Units of PPD. Nonreactors comprised 31586 children who did not wish to be vaccinated 27338 controls and 50634 vaccinees. Follow-up consisted of matching officially reported cases to the study records; this was discontinued in 1969. Tuberculosis rates were highest among the children who were most sensitive to tuberculin initially and about 75% of the subsequent tuberculosis came from the reactors. The rates were 30% lower among vaccinees than among controls. About 8% of the tuberculosis problems in this population could have been prevented by vaccinating all nonreactors. It is the opinion of the authors that BCG vaccination is indicated only when there is a high risk of becoming infected with tubercle bacilli. Because there is doubt about the possibility of identifying currently potent strains of BCG they recommend comparative trials in man using freeze-dried BCG in areas with a high risk of tuberculosis infection in order to determine which strains confer the greatest protection. (authors)
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Mycobacterium tuberculosis infections may be difficult to detect by the tuberculin test in populations where nonspecific tuberculin sensitivity (induced by BCG and "atypical" mycobacteria) is frequent. In those populations, the rate of M. tuberculosis infection can be determined by comparing the levels of sensitivity before and after BCG vaccination, and classifying as infected those who do not show increased sensitivity in the post-vaccination test. To test this method on a BCG-vaccinated population, a survey was carried out in a sample of 1,721 schoolchildren 6 to 10 years of age, from a suburban area of the city of Rio de Janeiro, where BCG vaccination had been carried out on a large scale. The results suggest that the method is valid for BCG-vaccinated populations, although its accuracy may be affected by the intrinsic variability of tuberculin tests and BCG vaccination, by the action of infections with non-tuberculous mycobacteria, and by low infection rates. The tuberculous infection rate found in the sample group (4.13%) was compared with the results of a tuberculin survey carried out in the same area in 1970, and the incidence of infection was found to be decreasing by 7.68% annually. The annual risk of tuberculous infection for 1986 was 0.36 or 0.51%, depending on the mathematical model used for the calculation. These figures are smaller than the official estimates derived from the incidence rates of notified cases or from surveys made before intradermal vaccination was adopted. This may be due to methodological error, inaccuracies of notification data, association between age and risk of infection and/or peculiarities of the surveyed area.
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BCG revaccination in the Sverdlovsk Region is performed thrice: at the age of 5, 10 and 15 years. The percent of children covered by tuberculin diagnosis and BCG vaccination is growing. Complications of BCG vaccination remain at the same level. Tuberculosis morbidity in children rises due to minor forms of tuberculosis. However, it is 2 times less than mean tuberculosis incidence in Russia. Primary infection is registered 4.5 times less frequently.
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Marked fluctuations in sensitivity to tuberculin related to the time of nonspecific vaccinations were found in children aged 1 to 7 years vaccinated with BCG within the first week of life in annual Mantoux test (2 tuberculin units). At the age of 3 and 7 years vaccinations raise sensitivity to tuberculin causing a rise in positive reactions to tuberculin. This indicates changes in postvaccination allergy to BCG.
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