Prevalence of Latent TB and Effectiveness of BCG Vaccination Against Latent Tuberculosis: An Observational Study

Anna Dahlgren-Aronsson,Vignir Sigurdsson,Birger Trollfors

doi:10.1016/j.ijid.2021.06.045

Anna Dahlgren-Aronsson, Vignir Sigurdsson + Show 1 more

Open Access

https://doi.org/10.1016/j.ijid.2021.06.045

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Abstract

This study aimed to determine the prevalence of latent tuberculosis infection (LTBI) in immigrant children and adolescents (aged 0-17 years) living or recently arriving in Sweden. It also aimed to estimate the effectiveness of Bacillus Calmette-Guérin (BCG) against LTBI in immigrant children coming to Sweden from high-incidence countries, most of them being asylum seekers. LTBI was defined as a positive Quantiferon or a tuberculin skin test (TST) of ≥ 10 mm in small children from whom it was difficult to obtain 3 mL of blood. A typical BCG scar was used as a substitute for written documentation of BCG vaccination. The study comprised 1,404 immigrants aged 0-17 years. The arms and legs of all of them were inspected for a BCG scar, and Quantiferon or TST was performed. The study was a retrospective, observational, comparative cohort study. LTBI was found in 123 of 1,011 (12%) children with a BCG scar and in 116 of 393 (29.5%) without a BCG scar, giving an estimated vaccine effectiveness of 59%. LTBI was common among the immigrant children (17%). LTBI can progress to active TB and then spread in the immigrant population and to the general population if all immigrant arrivals are not tested and given prophylactic treatment if they have LTBI. The BCG vaccine was found to have a significant effect on LTBI (59%).

Highlights

The licensed vaccine against tuberculosis (TB) – Bacillus Calmette-Guérin (BCG), which is an attenuated strain of Mycobacterium bovis – is the most commonly used vaccine in the world
Apart from the 1,532 patient records that were reviewed, another 301 immigrants were offered a health examination during the same time period but they did not come to the outpatient clinic, despite a reminder; 16% of all immigrant children were never tested for latent TB infection (LTBI)
All children aged < 17 years and arriving alone were given a trustee (“good man” in Swedish) after arrival, who acted as their guardian

Summary

Introduction

The licensed vaccine against tuberculosis (TB) – Bacillus Calmette-Guérin (BCG), which is an attenuated strain of Mycobacterium bovis – is the most commonly used vaccine in the world. It was introduced in 1921 (BCG vaccines: WHO position paper; Fritschi et al, 2020) and reached a worldwide coverage of > 80% in low- and middle-income countries in 2019 (GHO | By category, 2020) As it was introduced such a long time ago, it was not tested in double-blind placebo-controlled trials before its general use; both randomized trials and trials with other designs were later performed (Dye 2013; Mangtani et al, 2014; Barreto et al, 2006; Fine, 1995; Fine, 1988; Hart et al, 1977; Roy et al, 2014; Behr, 2002; Katelaris et al, 2020; Michelsen et al, 2014; Colditz et al, 1994). If latent TB infection (LTBI) progresses into active TB, usually pulmonary contagious TB, it can spread to nonimmune healthy individuals who develop LTBI, which can be activated and contagious

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