Risk factors for croup in children with recurrent respiratory infections: a case-control study

Croup accounts for approximately 15% of all lower respiratory disease in children, but little is known about risk factors or its recurrence rate. The aim of this study was to determine the risk factors for croup and recurrent croup and to find out whether it is possible to predict the course of the disease. We considered croup patients who visited the Paediatric Department of Oulu University Hospital as primary health care patients at night during 1996-2000. For most analyses we used sex- and age-matched control patients who had had other respiratory infection but for environmental factors we used population controls. We performed conditional logistic regression analysis on data applying to 182 pairs of patients and controls. The recurrence rate was high, as 61% of the croup patients had had at least three episodes. Family history of croup was the most significant risk factor for both croup itself and recurrent croup. In multivariable analysis the odds ratio (OR) for the parents having a history of croup was 3.2 (95% CI 1.5, 7.1, P < 0.01) and 4.1 (95% CI 1.4, 11.7, P < 0.01) for recurrent croup. Parental smoking appeared to be a risk factor for respiratory infections but not for croup. Patients with croup had a cat as a pet less often than the controls, with OR 0.5 (95% CI 0.2, 1.0, P = 0.04). Family history appeared to be an exceptionally strong predictive factor for croup and its recurrence. In this patient series prone to respiratory infections recurrence of croup was common.