Prevelence of latent tuberculosis and associated risk factors in children under 5 years of age in Karachi, Pakistan

Abstract

Background: As infected children represent a large proportion of the pool from which tuberculosis (TB) cases will arise and its associated risk factors that influence TB infection are basic cause for burden of TB. Aim: This study was to determine the prevalence of latent TB and associated risk factors in children less than 5 year of age in Karachi, Pakistan. Setting and Design: Cross-sectional study and it was conducted in tertiary care hospital in Karachi. Materials and Methods: In this study, children who were living in contact with individuals who had proven smear-positive pulmonary TB cases were investigated. A tuberculin skin test (TST) was performed on each child. TST sizes ≥5 and 10 mm, respectively, were considered positive. Statistical Analysis: A random effects logistic regression model, which takes into account the clustering of contacts within households, was used to assess the relationship between the tuberculin response of the contact and risk factors. Results are reported as unadjusted and adjusted odds ratios and their 95% confidence intervals. The likelihood ratio test was used to assess the overall significance of risk factors, tests for trend, and tests for interaction. Results: The distribution of TST responses followed a bimodal pattern, with 135 (35%) children presenting a palpable induration. The risk of positive TST response in the child increased with the geographic proximity of the child to the individual with TB within the household and with the degree of activities shared with the individual with TB. Nutritional status and presence of a bacille Calmette-Guérin (BCG) scar were not independent risk factors for TST positivity in this population. On multivariate analysis, the effect of geographic proximity to the individual with TB, household size, and duration of cough in the index case persisted for TST responses ≥5 mm. Conclusions: Positive TST in a child reflects most probably TB infection rather than previous BCG vaccination. Contact tracing can play a major role in the control of TB in Pakistan.