2.3.1. Hospital Discharge Records

The ED discharge record is included among the administrative healthcare data routinely collected. At the end of each ED access, ED discharge records periodically were sent to the Regional Authority. The ED discharge records include various data such as the main diagnosis field coded by the ICD-9-CM system, the procedures and treatments administered during the ED access, the way of admission and discharge, and the severity of the condition at the access time. Administrative healthcare data such as ED discharge records display weaknesses in terms of sensitivity and specificity. Incidence rates and other variables were defined by using data extracted from this registry, selecting all hospital admissions with a main diagnosis of varicella or its complications (International Classification of Diseases, Ninth Revision (ICD-9-CM) codes. (Table 1).

ICD-9-CM codes were used to select subjects with varicella.