Epidemiology of the koch phenomenon of infants after bacillus calmette-Guerin vaccination by interferon-γ release assay status, Japan, 2013-2019.

BACKGROUND

The epidemiology of infants who exhibited the Koch-like phenomenon after Bacillus Calmette-Guérin vaccination and who subsequently tested positive in interferon-γ release assay (IGRA) was compared to that of those who tested negative. The reports of pediatricians on the phenomenon to the health authorities of Japan were retrieved and analyzed.

METHODS

In 2013-2019, 790 infants with such events were reported with IGRA test results available, of whom 81 (10.3%) tested positive and 709 (89.7%) negative.

RESULTS

The infants who were IGRA positive did not show an increasing trend (P = 0.06, P = 0.60), whereas those who were IGRA negative showed a significantly increasing trend (P = 0.42, P = 0.0002). The infants who were IGRA positive did not exhibit seasonality, whereas those who were IGRA negative had a higher number of cases in winter than in summer. The rates of infants who were IGRA positive per 10 million live births showed a significant correlation with the tuberculosis (TB) notification rates by prefecture (P = 0.41, P = 0.004), whereas those who were IGRA negative did not (P = 0.04, P = 0.78).

CONCLUSION

The IGRA-positive infants were distributed quite differently from those who were IGRA negative and appeared more likely to be infected with TB. Reports of pediatricians on the Koch-like phenomenon should continuously be collected as the reports reflect a risk of TB infection including TB outbreaks among infants in Japan. The reports should include IGRA test results as IGRA is more specific than tuberculin skin testing. Infants with IGRA-positive results should be followed up for 2-3 years to determine their final outcomes.