The immune system walls off the microbes in most infected people, keeping them healthy. But some infected individuals develop the active form of the disease, with symptoms such as a bloody cough, chest pain, fever, weakness and loss of appetite. The researchers focused on investigating how often children catch TB from an infected family member and go on to develop the active disease.
Martinez and his colleagues compiled information on TB risk in children from researchers around the world, pooling data from 46 smaller studies conducted since 1998 in 34 countries. The data tracked 137,647 children, starting when a family member or other close contact was diagnosed with active TB. Each child was followed for an average of four years. In addition to tracking TB cases, the researchers also evaluated several other factors, including the effect of medications given to children and other family members to try to prevent the bacteria from spreading.
In the study, 1,299 children were diagnosed with active TB within 90 days of their initial evaluation. Another 999 cases of the active disease were diagnosed during the follow-up period.
Historical data had shown that children younger than 1 who were infected with the bacteria had about a 20% chance of developing active TB. The historical data indicated that the risk of developing the active disease dropped to about 10% for TB-infected children ages 1-2, and to 5% for those ages 3-5. In contrast, the new data show that the risk of developing the active disease is 19% among infected children as old as 5. Among children ages 5-19, the risk of developing active TB after an infection is 8-12%, also higher than historical estimates.
Children with HIV were much more likely to develop active TB than those without HIV, the study found, mirroring a trend observed in adults.
‘We’re not catching them soon enough’
Preventive medications given to healthy children were quite effective if given before children became ill with TB, reducing the development of active TB disease among TB-infected children by 91%. In many cases, however, children developed TB symptoms before they received any preventive medications.
“We can only give preventive therapy to children who have not progressed to full-blown TB disease,” Martinez said. “Since children who are exposed to TB develop the disease so quickly, it is difficult for health care providers to find these children in time to provide the preventive treatment. We’re not catching them soon enough.”
Martinez and his colleagues hope their findings will help public health experts better focus their TB prevention efforts, especially in identifying TB cases faster to better prevent their spread to children.
“Tuberculosis is something that’s been perplexing people for thousands of years,” he said. “In particular, there are a lot of knowledge gaps in our understanding of pediatric TB. If we don’t dedicate attention to it, it will continue to be the No. 1 killer among infectious diseases.”
Other Stanford co-authors of the work are former graduate student Olivia Cords; former Stanford medical student Nathan Lo, MD, PhD; and Julie Parsonnet, MD, professor of medicine and of health research and policy.
Andrews and Parsonnet are members of the Stanford Maternal & Child Health Research Institute. Andrews is also a member of Stanford Bio-X and the Stanford Woods Institute for the Environment. Parsonnet is a member of the Stanford Cancer Institute.
Robert Horsburgh, MD, of Boston University, was also a member of the study’s primary analysis and writing group. The paper was co-authored by 90 other members of the Pediatric TB Contact Studies Consortium. They work at institutions around the world.
The research was funded by the National Institutes of Health (grant T32 AI 052073).
Source: Stanford Medicine