Pertussis in South Australia 1893 to 1996.

This study describes trends in reports of pertussis in South Australia. Data were analysed from three sources: mortality data since 1893 from South Australian yearbooks, notification data from 1917, and hospitalisation data for pertussis or related complications since July 1985. Crude and age-specific rates of mortality, notifications and hospitalisation were compared. Pertussis peaked in 3 to 5 yearly cycles. The mortality and notification rates have generally declined over time. However, since 1993 the notification rate has remained high. The median age for pertussis notifications increased from 4 years in 1984 to 15 years in 1996. Serological testing for pertussis was included in 15% of notifications in 1985 and 90% in 1996. The age specific hospitalisation rate for pertussis was highest in infants < or = 6 months. Since the turn of the century, mortality and notification rates due to pertussis have declined. Over the past decade the major burden of severe disease resulting in hospitalisation has been borne by infants < or = 6 months. These infants are too young to be afforded protection from three primary immunisations against pertussis. Despite no substantial increase in mortality nor hospitalisation for pertussis in South Australia, the notification rate has remained high since 1993. This increase may be attributable to the use of more sensitive tests for pertussis, such as serology.