Recurrent and non-recurrent croup: an epidemiological study

A community-based study investigating the natural history of recurrent and non-recurrent croup is described. Daily temperature data were collected during 1977-83, in order to analyse seasonal variation and the effect of atmospheric temperature on the number of croup episodes per calendar month. A case-control study of 137 cases--consisting of 75 children with recurrent croup and 45 children with non-recurrent croup--and 236 controls matched by age and sex was also conducted. It aimed to study associations between croup and other selected diseases in the patients and their families. Recurrent croup differed from non-recurrent croup in its natural history in a number of ways. There was a winter and autumn peak in the number of episodes per month. These episodes occurred on days with significantly lower maximum and minimum temperatures. Recurrent croup was significantly associated with a patient history of asthma and wheezy bronchitis and a family history of croup. In contrast, non-recurrent croup showed an autumn peak only, as well as no association with atmospheric temperature or other disease in the patients and their families. This study confirms and extends observations indicating that recurrent croup involves a persistent and inherited airways hyper-reactivity that is triggered by viral and other stimuli, including those related to temperature.