Heilbrigðisskýrslur - 01.12.1980, Síða 132

Identification of Epidemic Waves
For measles, a direct comparison of Iceland with countries with larger
populations and more continental locations is instructive. Figure 1
shows the time series of reported cases between 1945 and 1970 for four
countries, arranged in decreasing order of population size. In the
United States, with a population of 210 million in 1970, epidemic
peaks arrive every year, and in Britain (56 million), every two years.
Denmark (5 million) has a more complex pattern, with a tendency to a
three-year cycle in the latter half of the period. Iceland (0.2 million
stands in contrast to the other countries in that only eight waves
occurred in the 25-year period, and several years are without cases.
If we extend our study of Iceland back to the beginning of regularly-
published volumes of data on public health in Iceland, then the separate
nature of the epidemic waves becomes still clearer. For the eighty
years between 1896 and 1975, some 90.000 cases are recorded. All but
a handful of these are concentrated into sixteen distinct outbreaks
or waves (numbered I through XVI in Table 1). During the 304 'epidemic'
months the average incidence of reported measles cases was 294 each
month; in the 644 'nonepidemic' months, on average only 2 cases were
reported each year. The table shows the striking difference between
the earlier waves—which were separated by long time intervals but
had high number of cases and a significant death rate—and the later
period in which waves followed each other in regular succession, at
more frequent intervals, had a lower number of cases, and a nil or very
low death rate.
Spatial spread of measles
Each measles wave displays a distinctive pattern of spread. In the
book, the sixteen waves were mapped in detail. Figure 2 gives an
example of one such outbreak, Wave V, which began in the late sommer
of 1928 and lasted until the end of the next year. Over the seventeen
months, the total number of recorded cases was 5.317, an attack rate
of 50.8 per 1000 population. The number of deaths attributed to
measles was 16, a death rate of 3.0 per 1000 cases. The wave has a
single peak in January 1929.
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HEILBRIGÐISSKÝRSLUR 1980