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By Hal B. Jenson, MD, FAAP
Dean, Western Michigan University School of Medicine, Kalamazoo, MI.
Dr. Jenson reports no financial relationship in this field of study.
SYNOPSIS: TB rates among pre-school aged children in the United States are 32 times higher in foreign-born children and six times higher in U.S.-born children with at least one foreign-born parent, compared to U.S.-born children with U.S.-born parents.
SOURCE: Pang J, et al: Epidemiology of Tuberculosis in Young children in the United States. Pediatrics 2014;133:e494.
A cross-sectional population-based study of TB in children was conducted in 2005-2006 among a consortium of 20 enrollment sites, primarily sites having statewide jurisdiction. The prevalence study included children <5 years of age diagnosed with TB and having at least one foreign-born parent. An observational study collected demographic and clinical information.
A total of 364 cases of TB were identified, which represented 49.6% of all TB cases among young children reported to the National TB Surveillance System in 2005 and 2006. More than 80% (n=303) of the children were born in the United States, including 194 (64%) with at least one foreign-born parent and 76 (25%) with both U.S.-born parents. The parents' birth countries were unknown in 33 (11%) of the children.
Estimated TB rates per hundred thousand population for children <5 years of age were 2.57 for all children; 24.03 for foreign-born children; 4.81 for U.S.-born children with at least one foreign-born parent; and 0.75 for U.S.-born children of U.S.-born parents. More than one-half of the cases (53%) occurred among U.S.-born children with at least one foreign-born parent.
A total of 149 children were enrolled in the observational study from among 255 eligible children, including 27 (44%) foreign-born and 122 (63%) US-born. The median age was two years. Two-thirds of the enrolled children were Hispanic. A total of 149 children were enrolled in the observational study from among 255 eligible children, including 27 (44%) foreign-born and 122 (63%) U.S.-born. U.S.-born children with at least one foreign-born parent were more likely than foreign-born children to be diagnosed with tuberculosis as infants (30% vs 7%); Hispanic (73% vs 37%); diagnosed through contact tracing (40% vs 7%); and have an identified source case (61% vs 19%). Two thirds of children were exposed to tuberculosis in the United States.
Childhood tuberculosis remains an enormous global burden with approximately 530,000 cases of TB disease and 74,000 deaths estimated in 2012 among non-HIV infected children. Of the almost 10,000 cases of tuberculosis that occur annually in United States, more than 1000 occur in children. Two-thirds of cases in children and adolescents have at least one foreign-born parent.
The results of the study show that — compared to U.S.-born children with U.S.-born parents — foreign-born children in the United States have tuberculosis rates 32 times higher. U.S.-born children with at least one foreign-born parent have tuberculosis rates six times higher. Because of these relatively high rates of TB, U.S.-born children of foreign-born parents account for most cases of tuberculosis in the United States among children <5 years of age.
The basis of the increased risk for tuberculosis by having a foreign-born parent is unclear. This may be a marker for foreign travel, or for foreign visitors to the home who have undetected, active tuberculosis. Visitors to the United States are not screened for latent tuberculosis.
The results underscore two important points. First, tuberculosis in low-burden countries such as the United States cannot be eradicated until there is better control in the high-prevalence countries from which the U.S. receives many immigrants and visitors. It is only been since 2009 that children 2-14 years of age immigrating to United States are routinely tested for latent tuberculosis, though immigrants older than 14 years of age are not tested for latent tuberculosis. Second, the management of the adult source cases necessitates effective contact investigations that identifying young contacts, followed by targeted testing and treatment of latent tuberculosis infections in those children.