A Prospective Study of Bacillus Calmette-Guérin Scar Formation and Tuberculin Skin Test Reactivity in Infants in Lima, Peru

Abstract

ABSTRACT. Objectives. To determine the sensitivity of the bacillus Calmette-Guérin (BCG) scar as an indicator of previous vaccination and to ascertain the tuberculin skin test (TST) response in infancy after vaccination in a community from an area hyperendemic for tuberculosis (TB).Methods. In a birth cohort of healthy term infants from Lima, Peru, a single dose of BCG vaccine was administered within the first month of life. Scar formation was assessed biweekly during the first 6 months and again at 3 years after vaccination. TST response was evaluated 6 months after vaccination.Results. Six months after vaccination, 99% (68) of the newborns exhibited a BCG scar (>2 mm). Scar size did not differ by sex, birth weight, age at vaccination, or nutritional status in the first 2 months. Eighty percent of the participants were found 3 years after vaccination, and all of them had a BCG scar. Mean TST reaction size 6 months after vaccination was 2.9 ؎ 0.3 mm. No association was found between sex or age at BCG vaccination and TST size. Only 3 children had a TST >10 mm, and the 3 had a TB contact at home.Conclusions. The BCG scar was a sensitive indicator of vaccination status up to 3 years after the administration of the vaccine in the first month of life. Although nearly a quarter of the children had a TST response >5 mm 6 months after vaccination, TST reactions >10 mm did not occur in the absence of exposure to a person with tuberculosis. A cutoff of 10 mm should be used for disease control purposes in people who are born in countries where TB is endemic. The presence or absence of a BCG scar is often used as an indicator of previous vaccination in clinical settings as well as surveys performed by health institutions such as the Expanded Program on Immunization to assess vaccine uptake. 7 However, the sensitivity of the BCG scar as an index of vaccination status is still the subject of controversy. 6 Failure to form a scar may be related to factors such as lack of maturation of the immune system, 8 faulty technique, or use of a nonpotent vaccine. 9 In Peru, intradermal administration of BCG is given at birth at any health facility, such as a hospital or health post. This is part of the regular immunization program following WHO guidelines. 10 Since 1991, the same strain of BCG has been used across the country. In 2000, the estimated incidence of active pulmonary TB in Peru was 111 cases per 100 000, 11 but in one area, it has been reported to be 364 per 100 000 12 despite 95% coverage of BCG vaccination at birth and a human immunodeficiency virus prevalence of Ͻ0.5%. 11 In countries with such a high TB incidence, diagnostic algorithms include the tuberculin skin test (TST) as a screening tool, particularly in children. 13,14 It has been shown that the BCG may affect the TST by factors such as strain and dose, 15 number of vaccines administered, 16,17 time since vaccination, 18 age and nutritional status, 19 and method of vaccine administration. 20 However, the scope of these effects is unclear. Therefore, for the TST to...

Changes in Tuberculin Skin Test Positivity Over 20 Years in Periurban Shantytowns in Lima, Peru

“…The community prevalence of TST positivity is an important indicator of TB control because it is not confounded by changes in TB case finding that can considerably increase or decrease estimates of the incidence of TB disease. 5 In TBendemic countries such as Peru, the TST is the only widely used method for diagnosing latent infection, especially in children [7][8][9][10] despite difficulty interpreting results in subjects who have received the Bacille Calmette-Guérin (BCG) vaccine. The great majority of children in Peru receive the BCG vaccine at birth.…”

Scar Formation and Tuberculin Skin Test Response After Bacillus Calmette-Guerin Vaccination: Does Prematurity or Low Birth Weight Have an Impact?

“…A "visible scar" was defined as a scar measuring 2 or more millimeters. Scar failure rate was 1.4% (23).…”

Is there a correlation between the size of the BCG scar and renal scar of urinary tract infections in children?

“…12 The authors reported that scars do not form when immune system of the infants is not fully mature, and in cases of vaccination performed using an improper technique or an impotent vaccine. 13 At least one BCG scar was present in our entire patient group, and none of our patients was immunosuppressed. A positive correlation was found between age and horizontal and vertical diameter of BCG scars in this study.…”