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[Predictive value of the standardized tuberculin test in children vaccinated with BCG]
1Departamento de Epidemiologia da Faculade de Saúde Pública da USP, Brasil.
Insights
The tuberculin test
Area of Science:
- Pediatric Infectious Diseases
- Immunology
- Public Health
Context:
- Tuberculin testing in BCG-vaccinated children under five is controversial.
- BCG vaccination coverage is high, but tuberculosis infection prevalence is low in the study region.
- Assessing test accuracy requires understanding BCG-induced vs. natural tuberculin sensitivity.
Purpose:
- To analyze the predictive positive value of the tuberculin test in young children previously vaccinated with BCG.
- To quantify the decline of BCG-induced allergy and the rise of natural tuberculin sensitivity with age.
- To estimate the impact of these factors on test applicability in clinical and epidemiological settings.
Summary:
- Calculated declining BCG-induced allergy and increasing natural tuberculin sensitivity from ages 1 to 7.
- Estimated false positive rates and predictive values for tuberculous infection from ages 1 to 5.
- Found high probability of strong reactions due to BCG, limiting test utility.
Impact:
- The tuberculin test's predictive value increases with age but remains limited in this population.
- High rates of false positives due to BCG vaccination reduce the test's clinical and epidemiological applicability.
- Findings highlight challenges in using tuberculin tests for tuberculosis diagnosis in BCG-vaccinated children.
Abstract:
The applicability of tuberculin test in children under five years of age, BCG-vaccinated during their first year of life, is a controversial matter. With a view to clarifying the subject the predictive positive value of the test in a region of high BCG coverage and low prevalence of tuberculous infection was analysed. From the proportion of strong reactors among infants and school-age children, vaccinated and not unvaccinated, the declining rate of BCG induced allergy and the increment rate of naturally acquired tuberculin sensitivity between the first and the seventh years of life were calculated. Those calculations allowed for the estimation of the respective values for the intermediate ages. The numbers of false positives to be expected were calculated by difference. Knowing the sensibility and the specificity (1 - FP) of the test, the BCG coverage and the prevalence of infection, the predictive values for tuberculous infection were: 1.52%, 4.22%, 8.26%, 14.86% and 23.00%, respectively from the first to the fifth years of life. Under these conditions, the probability of a strong reaction being provoked by BCG is very high, decreasing the applicability of the test both in clinics and epidemiology.