Laboratory-confirmed PIA-infections were reported by the Institute of Virology and Immunobiology. For all identified PIAH patients <18 years of age a medical chart review was conducted by a representative of the study coordination centre (University Children's Hospital, Wuerzburg). Date of admission, number of days in hospital, data on treatment, demographic, clinical and epidemiological data were obtained using a standardized and anonymous data collection form. All data were collected for the duration of hospital stay.