Rapid detection of pandemic influenza in the presence of seasonal influenza

摘要

Key to the control of pandemic influenza are surveillance systems that raise alarms rapidly and sensitively. In addition, they must minimise false alarms during a normal influenza season. We develop a method that uses historical syndromic influenza data from the existing surveillance system 'SERVIS' monitoring seasonal ILI activities in Scotland.Materials and methods We develop an algorithm based on WCR of reported ILI cases to generate an alarm for pandemic influenza. WCR is defined as the ratio of the number of reported cases in a week to the number of cases reported in the previous week.From the seasonal influenza data from 13 Scottish health boards, we estimate the joint probability distribution (Figure 1) of the country-level WCR and the number of health boards (denoted by N_HB) showing synchronous increases in reported influenza cases over the previous week. Pandemic cases are sampled with various case reporting rates from simulated pandemic influenza infections (using an individual-based stochastic model of the spread of pandemic cases in Great Britain) and overlaid with seasonal SERVIS data from six influenza seasons 2001-2007. A typical influenza season in a temperate country like Scotland is of 33 weeks. Although pandemic influenza can start any time of the year, in order to overlay simulated pandemic cases with seasonal ILI cases, we consider only these 33 weeks as pandemic starting weeks.