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TB rates declining among US children, but disparities persist
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Although the rate of new tuberculosis cases among U.S. children and adolescents has decreased by nearly half in recent years, incidence of the disease remains disproportionately high among certain ethnic, racial and geographic communities, researchers reported in The Lancet Public Health.
Using data from the National TB Surveillance System (NTSS) and U.S. Census Bureau, Tori Cowger, MPH, from the Harvard T.H. Chan School of Public Health, and colleagues evaluated TB incidence rates among children and adolescents from 2007 to 2017. They then analyzed trends by race, ethnicity and parental country of birth as well as in U.S. territories, including American Samoa, Guam, Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands, and freely associated states, including the Federated States of Micronesia, Marshall Islands and Palau.
Significant disparities in incidence
During the study period, 6,072 cases of TB among U.S. children and adolescents were reported to the NTSS, with a rate of one case per 100,000 person-years. Overall, this represented a significant 47.8% decrease from 1.4 per 100,000 person-years in 2007 to 0.8 per 100,000 person-years in 2017.
However, incidence rates varied considerably by race or ethnicity. For instance, when compared with white children and adolescents, the rate of new TB cases was at least 14 times higher among all other racial or ethnic groups during the study period. Specifically, the rate among white children and adolescents was 0.1 per 100,000 person-years vs. 4.4 per 100,000 person-years among Asian youths, 1.9 per 100,000 person-years among black youths and 1.8 per 100,000 person-years among Hispanic youths. Incidence rates were even higher among Native Hawaiian or Pacific Islanders (14.4 per 100,00 person-years).
In terms of birthplace of both child and parents, the incidence rate was highest among children born outside the U.S. (6.5 per 100,000). However, rates were still higher among those born in the U.S. but with at least one parent born outside the U.S. than among U.S.-born children whose parents were also both born in the U.S. (1.7 vs. 0.3 per 100,000 person-years). Risk for TB also increased if both parents, as compared with only one parent, were born outside the U.S. (2.4 vs. 1 per 100,000 person-years).
The researchers also found that incidence rates were higher among children and adolescents living in U.S.-affiliated islands, accounting for 15% of overall TB cases, when compared with children and adolescents living in U.S. states (11.7 vs. 1 per 100,000 person-years). This was particularly true for those living in the Marshall Islands and Federated States of Micronesia, where incidence rates were greater than 150 per 100,000 person-years. Cases in these islands also accounted for 11% of the overall TB burden and more than half of all TB deaths during the study period, despite representing less than 0.1% of the estimated population.
“These wide-ranging and pervasive disparities probably reflect structural inequalities that give rise to disproportionate exposure, vulnerability to infection and disease, and unequal access to prompt diagnosis and treatment. The findings suggest that TB care prevention strategies in the U.S. are succeeding in reducing overall burden among children and adolescents, but more attention and possibly new approaches are needed to address the inequalities,” Cowger said in a press release.
Questions about diagnosis
Of the TB cases seen among children and adolescents from 2007 to 2017, symptoms prompted diagnoses in 37% of cases. However, diagnoses were made after contact investigations in only 10% of children born outside the U.S. vs. 41% among those born in the U.S. Culture confirmation of the disease occurred in 39% of children and adolescents and was more common among adolescents than children (69% vs. 30%).
Approximately two-thirds of children younger than 15 years with TB in the U.S. from 2007 to 2017 would have been recommended for TB testing under current targeted testing guidelines, the researchers noted. During the study period, 38% were identified through contact tracing, 21% were born outside the U.S. and 8% traveled outside the U.S. for at least 2 months. Although 21% did not meet guidelines for testing, they did have at least one parent abroad. The remaining 13% had none of these characteristics reported, according to the data.
“Two-thirds of children with TB diagnosed in the U.S. states had at least one risk factor covered by current clinical practice guidelines. Nevertheless, a third of TB cases occurred outside of the groups currently identified for targeted testing, highlighting the need to consider additional characteristics, such as parental place of birth, in appropriate settings, to improve TB care and prevention,” Cowger said.
‘Cautious optimism’
In a linked comment, Michael Lauzardo, MD, MSc, and Meghan Nodurft-Froman, MPH, both from the Southeastern National TB Center, University of Florida, Gainseville, noted that this study offers “generally good news.”
“Imagine the incidence of any other disease decreasing by almost half within a 10-year period. This trend should be encouraging to those working to eliminate tuberculosis and provide evidence that current strategies of control, including early initiation of therapy, screening of close contacts and aggressive treatment of latent tuberculosis infection, are highly effective when applied consistently,” they wrote. “However, these data are overshadowed by the most important finding of this report: the stark disparity between various subpopulations.”
Lauzardo and Nodurft-Froman cited the extremely high incidence in the Marshall Islands and Federated States of Micronesia as evidence that national TB programs can do more to address the limitations of current approaches.
“These findings give grounds for cautious optimism, however daunting the task of elimination might be. Tuberculosis control efforts work but need proper leadership, guidelines should be adjusted to address disparity within populations, and a better understanding of the social determinants of tuberculosis is needed if we are to keep on the path toward elimination,” they wrote. – by Melissa Foster
Disclosures: This study was funded by the CDC. The authors report no relevant financial disclosures. Lauzardo and Norduft-Froman report no relevant financial disclosures.
Perspective
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Jeffrey R. Starke, MD
Children have been described as the “yellow canaries” of tuberculosis — after the practice of miners using birds to detect poison gases — because they tend to develop TB disease much sooner after infection than most adults. When TB resurged 20% in the U.S. in the late 1980s and 1990s, the incidence in children rose almost 40% and was a harbinger of the increase in adults. This tendency for early progression to disease has both bad and good implications: On the one hand, the ill child may be the index case, presenting for medical attention before her contagious source case; on the other hand, interventions such as prompt contact tracing for an adult case can prevent a large proportion of childhood TB cases. Accordingly, understanding the current epidemiology of childhood TB is a crucial quality measure for TB programs.
This important study by Cowger et al, which is the first comprehensive review of childhood TB in the U.S. since 2010, demonstrates a 48% decline in incidence over just 8 years. The study also provides rich detail about the heterogeneity of cases based on race and ethnicity and geographic considerations, namely the birthplace and travel for the child and the birthplace of the parents. How did this decline come about in the U.S.? The basic tools of TB control have not changed in decades; they remain epidemiologic assessment of risk, contact tracing of suspected and verified cases, tests of infection (the tuberculin skin test [TST] and the interferon-gamma release assays [IGRAs]), physical examination, chest radiography and appropriate treatment of TB infection and disease with safe, inexpensive and effective drugs. The decline has been caused, in large part, by the improved application of these rather ancient tools. WHO estimates that in 2018, 1 million children younger than 15 years developed TB and 233,000 died. The true tragedy of global childhood TB is the lack of use of these inexpensive and effective tools of prevention and early intervention in the highest burden countries.
Although the progress toward TB elimination in the U.S. has been encouraging, this study also demonstrates how difficult it will be to achieve. As one example, 34% of the children younger than 15 years would not have met current guidelines for targeted testing for TB infection. While expanding current guidelines to include children with at least one parent born abroad in a high TB burden country would have reduced this to 13%, the mass testing of children in this latter category would add millions of children to the denominator to prevent just a few hundred cases. Given the notorious issues with the specificity of the TST and IGRAs, this mass testing also would create a large number of false-positive tests.
At my institution, we are currently caring for three young U.S.-born children with central nervous system TB; the source case for the first was a non-U.S.-born grandfather, for the second it was a U.S.-born grandfather, and the third source case has not yet been found. In all three cases the child became very ill before the source case was discovered and the families were living in impoverished circumstances. Targeted testing would not have prevented any of these cases. It has been stated that TB thrives on human misery, and the study authors point out the importance of social determinants of health — food security and nutrition, access to economic and material resources, residential segregation, exposure to secondhand smoke, indoor and outdoor air quality, and health care policy, access and infrastructure — in assessing TB risk. Developing an “endgame” for TB elimination will be extremely challenging and will require both better tools and more progress in eliminating health disparities in general.
Baylor College of Medicine
Houston
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