Prevalence of tuberculosis in migrant children in Switzerland and relevance of current screening guidelines
Authors: Boukamel Myriam , Fougère Yves , Gehri Mario , Suris Joan Carles , Rochat Isabelle , Miletto Damien , Kyrilli Spyridoula , Fouriki Athina , Crisinel Pierre Alex 
Published: June 2020

AIMS
Since 2016, Swiss guidelines recommend screening of all migrant children <5 years of age for tuberculosis (TB) and to screen older children only if they have risk factors for tuberculosis. Our goals were to describe the epidemiology of latent tuberculosis in migrant children at the Lausanne University Hospital, to identify determinants of latent tuberculosis and tuberculosis disease, and to evaluate the risk of a false-positive tuberculin skin test when using a positivity limit of 5 mm.

METHODS
Newly arrived migrant children 0–18 years of age were prospectively enrolled from 31 August 2015 to 31 August 2017. Every migrant child was assessed for the risk of tuberculosis exposure and tuberculosis disease and was administered a tuberculin skin test. A tuberculosis-spot test was performed in children ≥5 years of age when the tuberculin skin test was positive. Children with clinical and/or radiological signs of tuberculosis disease were further investigated. Children ≥5 years of age with a positive tuberculosis-spot test and children <5 years of age with a positive tuberculin skin test, without clinico-radiological signs of tuberculosis disease received a diagnosis of latent tuberculosis. A false-positive tuberculin skin test result was diagnosed in children ≥5 years of age when the tuberculosis-spot test was negative. Potential determinants of tuberculosis (latent tuberculosis and tuberculosis disease) and of false-positive tuberculin skin tests were identified. Student’s t-test or the Kruskal-Wallis test were used for continuous variables and the chi-square test or Fisher’s exact test for categorical variables. All variables with a p-value <0.05 were included in a multivariate logistic regression model.

RESULTS
Two hundred and fifty-three patients were eligible for the study. The median age of the patients was 8.1 years (interquartile range [IQR] 4.5–12.8) and 104 (41%) were female. Twenty-four percent of the patients (62/253) came from a country with a moderate–high incidence of tuberculosis disease (≥80 cases per 100,000 individuals). Twenty-eight patients (11%) had positive tuberculin skin tests, and tuberculosis was confirmed in 17 (6.7%) of these patients (16 with latent tuberculosis and 1 with tuberculosis disease). On multivariate analysis, moderate–high incidence of tuberculosis disease in the country of origin (adjusted odds ratio [aOR] 18.8, 95% confidence interval [CI] 5.1–68.6; p <0.001), older age (aOR 1.1, 95% CI 1.0–1.3; p = 0.025), and contact with a tuberculosis disease patient (aOR 8, 95% CI 1.8–36.2; p = 0.007) were associated with a diagnosis of tuberculosis. Among the 23 children over 5 years of age who had a positive tuberculin skin test with measurement available, a measure between 5–9 mm was more frequent in case of a false-positive tuberculin skin test (5/9, 56% vs 0/14, 0%, p = 0.002). BCG vaccination was the only predictor of a false-positive tuberculin skin test (p = 0.03).

CONCLUSION
Screening migrant children ≥5 years of age for tuberculosis could confer a public health benefit even in the absence of other risk factors. The limit of tuberculin skin test positivity could be raised from ≥5 mm to ≥10 mm to decrease the rate of false-positive results. A national assessment of migrant children between the ages of 5 and 15 should be carried out to confirm our findings.