U-EPX levels and wheezing in infants and young children with and without RSV bronchiolitis.

An association between severe infant bronchiolitis due to respiratory syncytial virus (RSV) and subsequent wheezing is well documented. High levels of urinary eosinophil protein X (U-EPX) have been related to active disease in asthmatic children. The aim of this study was to analyse whether RSV bronchiolitis leads to an increase in U-EPX levels and whether wheezing is more common in children with high U-EPX values. Seventeen infants requiring in-ward care for verified RSV lower respiratory tract infection were followed and compared with age-matched controls. A reference group without a history of RSV bronchiolitis was also included. At inclusion at mean age 3.3 months and at follow-up at mean age 32.9 months, U-EPX levels were comparable in the RSV group. However, at follow-up at mean age 6.4 months, the RSV group had significantly increased levels of U-EPX compared with inclusion (median 167.8; range 46.2-470.7 vs. 122.8; 43.7-266.0 microg/mmol creatinine; P=0.023) and also significantly increased compared with the 6-month-old controls (167.8 vs. 93.0; 19.0-204.0 microg/mmol creatinine; P=0.0095). RSV infected subjects that experienced wheezing had significantly higher U-EPX values both at inclusion and at age 32.9 months than those who did not. Also, in the reference group (mean age 18.4 months), the children who had wheezed during the preceding year had higher U-EPX levels than those who had not wheezed. In conclusion, RSV bronchiolitis severe enough to require in-ward care produces a significant, but transient increase in U-EPX. Furthermore, a high U-EPX at baseline appears to be associated with an increased risk of future wheezing.