The 2005 Wellington influenza outbreak: syndromic surveillance of Wellington Hospital Emergency Department activity may have provided early warning.

OBJECTIVES: To assess whether the Wellington Emergency Department (ED) Respiratory Syndromic Surveillance System may have provided early warning of the influenza outbreak in Wellington schools during 2005, and as a result might have provided the opportunity for an earlier or more effective public health response.
METHODS: All events of respiratory syndrome, as defined by selected ICD 10 codes, were extracted from Wellington Hospital ED for the dates 1 January 2004 to 31 December 2006, and analysed using the Centers for Disease Control and Prevention (CDC) surveillance program, Early Aberration Reporting System (EARS). Daily events were analysed for total counts and by lifecycle age group. Seven day moving averages of the numbers of events were also calculated.
RESULTS: This study indicated that the surveillance system may have provided early warning of a potential respiratory outbreak. Regular exceedance flags were generated nine days prior to the initial notification received by Regional Public Health (RPH). The surveillance system also provided information on the type of illness (respiratory), the groups affected (5-14 year olds), and the progression of the outbreak (peak, end).
CONCLUSIONS: The surveillance system might have worked by providing early notification of the outbreak. This may have prompted RPH to earlier investigate the potential outbreak and may have led to an earlier response. IMPLICATIONS: Surveillance of Emergency Department activity may be useful for early public health response.