Diagnosing latent tuberculosis in international adoptees remains challenging

Article Outline

• Question
• Design
• Setting
• Participants
• Intervention
• Outcomes
• Main Results
• Conclusions
• Commentary
• Copyright

George SA, Ko CA, Kirchner HL, Starke JR, Dragga TA, Mandalakas AM. The Role of Chest Radiographs and Tuberculin Skin Tests in Tuberculosis Screening of Internationally Adopted Children. Pediatr Infect Disease J 2011;30: 387-91.

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Question 

Among recently immigrated, asymptomatic internationally adopted children (IAC), is a positive tuberculin skin test (TST) associated with an abnormal chest radiograph for tuberculosis (TB)?

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Design 

Prospective, cross-sectional study.

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Setting 

University-based adoption clinic in Cleveland, Ohio.

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Participants 

566 IAC who presented for routine post-adoptive care.

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Intervention 

Each patient underwent a standardized clinical examination and TST. Chest radiographs were recommended for children with TST induration ≥5 mm.

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Outcomes 

The association between TST induration and clinical outcome was assessed. The clinical utility of chest radiographs was evaluated.

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Main Results 

There was no difference in age, birth country, or nutritional status between IAC with TST induration of 0 to <5 mm and those with 5 to <10 mm; IAC with TST ≥10 mm were older, more chronically malnourished, and more likely to emigrate from Guatemala. Among children with TST ≥5 mm (35%), 4 IAC had chest radiographs that were initially interpreted to be abnormal and consistent with TB; ultimately none were diagnosed with TB.

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Conclusions 

The 5-mm TST cut point did not capture IAC with risk factors for latent TB infection or progression to TB disease, suggesting that this is not a useful screening threshold. In contrast, a 10-mm cut point identified IAC at risk for TB infection and therefore should be a more useful screening threshold.

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Commentary 

Diagnosing newly arrived IAC with latent tuberculosis infection (LTBI) is an ongoing challenge. The current standard for diagnosis, the TST, may yield false positive results due to BCG vaccination, and the probability-based cutoffs for a positive test can also lead to questions in children with TST results just under the cutoff. The article by George et al highlights the problems inherent in studying this issue. The association of a TST ≥10 mm with increasing age was not surprising, because previous studies showed that an increased risk of LTBI with increasing age defined LBTI by a TST ≥10 mm. However, the odds of a TST ≥10 mm were higher in Guatemala than in China, a country with a higher TB incidence, suggesting that differences in TST results by country may reflect factors other than LTBI, such as variations in BCG vaccination. Furthermore, some of the children with a TST ≥5 mm but <10 mm may have had LTBI. Up to 20% of IAC with a TST <10 mm on initial testing have a TST ≥10 mm on repeat testing, and repeat testing was not performed in this study. The study supports the currently used TST cutoff of 10 mm for diagnosis of LTBI in IAC, but demonstrates the difficulty of assessing such a question without a definitive standard. Studies of newer assays (eg, Quantiferon, T-Spot TB) face the same problem. Research in high incidence countries on test sensitivity and specificity in comparison to known TB exposure may provide the best opportunity to improve diagnostic tests for LTBI.