Mycobacterium tuberculosis infection is becoming increasingly common among children adopted from foreign countries, Dr. Anna Mandalakas and her colleagues reported.
Because of this risk, international adoptees should receive tuberculin screening as soon as possible after their arrival in their new country, wrote Dr. Mandalakas of Case Western Reserve University, Cleveland, Ohio, and her coauthors (Pediatrics 2007;120:610-6).
“In addition, because of the risk of a false-negative [screen] after recent exposure to M. tuberculosis or secondary to malnutrition, clinicians should consider repeating the screen 3–6 months after children arrive in their adoptive countries and when nutrition has improved,” they said.
The team performed a retrospective review of 869 adoptees (mean age 26 months) who presented to the International Adoption Clinic at the University of Minnesota, Minneapolis, from 1986 to 2001. In addition to receiving a tuberculin skin test, each child underwent a nutritional assessment that included measurements of weight, height, length, and body mass index.
Twenty-eight percent of the group had evidence of chronic malnutrition, and 5% had evidence of acute malnutrition.
Based on a previously published analysis of a subset of this group, the investigators expected to find M. tuberculosis infection in about 12 (1%) of the 869 children. The rate of infection was much higher, with 12% of the group (102) showing a tuberculin skin test (TST) induration of at least 10 mm.
The frequency of a positive skin test did not differ among birth countries nor was it related to the presence of malnutrition. However, the proportion of children with a positive skin test increased over the study period. When the investigators controlled for the effect of age, the odds of having an infection increased 7% for each year during the study period.
The risk also increased 142% for each additional year of age for children who were younger than 24 months at the time of screening, and 15% with each additional year of age for children older than 24 months at the time of screening. This linear age-adjusted risk was present in all birth regions, the authors wrote. “Although this increase mirrors global trends during the same period, the degree of increase is substantially greater and highlights the need to identify factors within the orphanage that contribute to these children's risk for infection.”
The significantly increased risk among younger children probably reflects their close contact with infected caregivers. Most of the adoptees came from orphanages in which they were age segregated, so it's unlikely that they contracted the infection from older children or community members, they wrote.
“Our data suggest that a significant portion of children who live in orphanages are exposed to infectious adults with active tuberculosis. In children with exposure to an infectious adult, the TST should be interpreted as positive when TST indurations are greater than or equal to 5 mm. Therefore, our study likely underestimates the number of children who would receive a diagnosis of M. tuberculosis infection if the history regarding tuberculosis exposure were available. In addition, children with recently acquired M. tuberculosis infection may not have fully developed their immune response and associated TST response,” the investigators said.
They suggested that that added screening such as chest x-ray and a repeat TST 3–6 months after arrival may be a good idea in internationally adopted children with TST indurations greater than or equal to 5 mm.
“Although our study did not demonstrate a statistically significant association between nutritional status and TST reactivity, this lack of association reflects the small number of children defined as severely malnourished in our study and the resultant limitations in power to complete nutritionally stratified analysis,” Dr. Mandalakas and her associates said. Previous studies have shown that malnourished children—especially severely malnourished ones—who have an associated impairment in T-cell function may not be responsive to the TST.