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10
Origin of
the epidemic
The course
of the
Epidemic.
marked in the records of London and Paris—where the epidemic prevailed in February and March—but
absent in the readings for Stockholm, Gothenberg, Copenhagen, Christiania and Amsterdam, in which no
winter epidemic occurred. In the epidemics of the nineties, a corresponding antecedent period of low
pressure, with the accompanying south-westerly winds and increased temperature, is not always conspicuous,
and it is of course, possible that the association observed in 1918 is fortuitous.
The time which elapsed between the low pressure period and the maximum epidemic mortality
was, in London, from seven to eight weeks. The winter epidemic reached its height, as judged by
mortality, in the 9th week of 1919, following a period of low pressure about 11th January. A later
depression of only a few days' duration occurred about the 19th February and this may possibly have
had some association with the slight recrudescence of influenza mortality shown in the records in April.
In should be noted that the particular week in which the maximum mortality occurs does not
necessarily stand in any fixed relation in respect of time to the inception of the epidemic. The maximum
mortality may be attained within three weeks of the earliest deaths, but the interval may be twice as
long or more. In Manchester, for instance, the deaths recorded from influenza do not attain a maximum
until the seventh week of prevalence in the autumn, while in Sheffield the maximum was attained in the
fourth week.
It is difficult to trace the movements of the epidemic owing to the veil which the war has drawn
over the incidence of disease in Europe. The official records available in regard to Eastern Europe
and the near East are too meagre to serve as means to trace with certainty the early history of the
epidemic in these localities It is stated by some to have had its origin in Germany, but the disease
was described by the Germans themselves as "Spanische Seuche" and by the Swedes as "Spanska
Sjukan." Indeed, so far as the civil population of Europe is concerned, public attention was first
directed in the Press to the presence of epidemic influenza by the outbreak at Madrid, which was reported
in May and reached its height towards the close of that month, thereafter rapidly subsiding. A Spanish
origin of the epidemic is not borne out, however, on further inquiry. Influenza was prevalent among
American troops in April, and a nexus seems thus to be established between the European epidemic and
an abnormal prevalence of influenza and pneumonia in New York which occurred in March. The
abnormal feature of this prevalence was the high fatality among young adults. I am indebted to Dr.
Guilfoy, Registrar of the Health Department of New York, for the following figures illustrating this.

Influenza and cerebrospinal meningitis were both prevalent among troops at the front early in
1918, but the London records of deaths from influenza and pneumonia during that time do not show
any alteration of age-incidence corresponding to that observed in the New York figures.
It therefore seems probable that the source of "Spanish" influenza is to be found in the outbreak
of a "mild grippelike disease" prevalent in New York and many other American cities in March and
April. The absence of any marked increase in the death rates of New York and Chicago, between April
and the advent of the autumn pandemic, certainly suggests that this spring prevalence was the
American equivalent of the European summer epidemic. It may be added that the weekly bulletin of
the New York^Department of Health for the week ended 16th March, 1918, refers to the weather
experienced during January and February, 1918, as "two months of the most severe weather which this
city has ever experienced."
The progress of the summer epidemic can be broadly traced throughout Europe by its effect upon
the weekly death-rates. In London the death-rate from all causes rose to a maximum in the week
ended 13th July; a week earlier the rate for Bombay was at the maximum. Munich, Hamburg,
Leipzig, Dresden, Cologne and Frankfort followed; thereafter in the next fortnight Christiania,
Gothenberg, Madras and Calcutta. A fortnight later Copenhagen, Stockholm and Berlin show a
maximum and, finally, in the week ended 17th August, Amsterdam.
The early incidence in Bombay and the long interval separating the maximum there from that
of Calcutta and Madras is especially worthy of note in view of the fact that the order of attack was
repeated in the autumn outbreak. Elsewhere, however, there is no approximation to the order of the
summer incidence. In London the height of the epidemic occurred in the week ended 9th November,
instead of, as in the summer, practically contemporaneously with Bombay, where the maximum had been
cached a month earlier; and during October the maximum had been attained first in Madras, Ber in,