Underlying diseases were documented in 43% of PIAH, with asthma (25% of all children with predisposing factors) reported as one of the most frequent conditions. These results are comparable to the 32-40% of cases with underlying diseases (predominantly led by asthma) reported by most other surveys on pediatric PIAH [8, 11, 12, 14] . Of 40 patients with underlying diseases, 10% received ICU treatment, in contrast to only 4% of 54 previously healthy patients, indicating a more severe course of disease in risk group children. However, the majority of children with underlying disease had an uncomplicated course of disease. It may be assumed that at least in part they were hospitalized for pre-emptive treatment and monitoring of possible complications. In contrast, a recent study from seven Austrian hospitals on PIA patients seeking emergency medical care reported underlying chronic conditions only in 13% of PIA patients <18 years of age [15] .