An exploratory method for estimating the changing speed of epidemic waves from historical data.
BACKGROUND
Historical data are necessary to establish long-term trends in disease incidence but pose analytical problems since their accuracy and reliability may be poorly specified.


METHODS
A robust measure of the spatial velocity, R(0A), of epidemic waves from space-time series is proposed using binary data. The method was applied to the historical records of influenza morbidity for the island of Iceland over a 61-year period of influenza seasons from 1915-16 to 1975-76.


RESULTS
The onset of influenza waves tended to speed up over the period studied and the three pandemic waves associated with viral shifts in influenza A [Spanish influenza H1N1 (1918-19), Asian influenza H2N2 (1957-58) and Hong Kong influenza H3N2 (1968-69)] spread more rapidly around the island and struck earlier in the influenza season than did inter-pandemic waves, even when the latter were equally intensive as measured by total number of cases and case incidence.


CONCLUSIONS
The potential for using R(0A) in a real-time context is explored using French influenza data.


CONCLUSIONS
The new measure of wave velocity appears to be applicable to those historical time series where breakdown into regional or local areas is available. The study is being extended to (i) other countries where similar influenza time series are available and (ii) to other diseases within Iceland.
Department of Geography, University of Cambridge, Cambridge CB2 3EN, UK.
Andrew D
AD
Cliff
Peter
P
Haggett
Matthew
M
Smallman-Raynor
D015331:Cohort Studies; D004196:Disease Outbreaks; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D007055:Iceland / Q000453:epidemiology; D053118:Influenza A Virus, H1N1 Subtype; D053121:Influenza A Virus, H2N2 Subtype; D053122:Influenza A Virus, H3N2 Subtype; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology*; D008297:Male; D008962:Models, Theoretical; D009017:Morbidity / Q000639:trends*; D011237:Predictive Value of Tests; D015995:Prevalence; D012680:Sensitivity and Specificity; D018571:Sentinel Surveillance; D013030:Spain / Q000453:epidemiology; D016019:Survival Analysis; D006113:United Kingdom / Q000453:epidemiology