Estimating the usual prevalence and incidence of acute illness in the community: Implications for pandemic influenza and bioterrorism preparedness

Background: Early clinical signs of influenza caused by a pandemic strain will presumably not differ significantly from those caused by other respiratory viruses. Similarly, early signs of diseases that may result from bioterrorism are frequently non-specific and resemble those of influenza-like illness. Since the time window for effective intervention is narrow, treatment may need to be initiated prior to a definitive diagnosis. Consequently, planning of medications, manpower and facilities should also account for those who would be treated for an unrelated acute illness. Objectives: To estimate usual patterns of acute illness in the community as a baseline for integration into pandemic influenza and bioterrorism preparedness plans. Methods: Between 2000 and 2003 we conducted 13 telephone surveys to estimate the usual incidence and prevalence of symptoms of acute illness in the community. Results: On average, 910 households were included in each of the surveys, representing about 3000 people. The compliance rates for full interviews ranged from 72.3% to 86.0%. In winter, on average, about 2% of the Israeli population (individuals) suffered each day from fever of ≥ 38°C, and about 0.8% during the other months. The prevalence of cough was higher, 9.2% in winter and 3% during summer. Daily incidence of fever ranged from about 0.4% per day in winter to about 0.2% in the fall. The prevalence and incidence of both fever and cough were highest for infants followed by children aged 1-5 years. Conclusions: These background morbidity estimates can be used for planning the overall treatment requirements, in addition to actual cases resulting from pandemic influenza or a bioterrorist incident.