According to Carnwath, the age incidence showed curious changes. During the 1918 summer wave the ages most affected were 15 to 45. In the winter of 1918–19 there was a considerable shifting toward the extremes of life and particularly toward the younger years. The susceptibility of young children was the subject of a special inquiry in London. Though the attack rate was below the average, the chances of recovery were less than in other age groups. Of breast-fed infants, 30 per cent. contracted the disease; of artificially-fed 54 per cent. The opposite, however, occurred in lying-in homes. An inquiry in Cheshire revealed that 25.4 per cent. of expectant mothers affected died.
Renon and Mignot have made a report on the 1920 recurrence. According to them the grip of 1920 attacked all ages, in contradistinction to the 1918 epidemic, which attacked especially the young and vigorous. One-third of their group were over 40 years of age, while some were 70 and 80 years old. In spite of this the disease remained relatively mild.
Age morbidity in previous epidemics.—Previous to the epidemic of 1889–93, the various recorded observations regarding morbidity, and particularly regarding age morbidity, have consisted often of records made by practising physicians, and are merely estimates based upon their clinical experience and varying with the type of individual treated by them. Or else they have been records made by non-medical historians. During the 19th century, the tendency toward statistical enumeration becomes more and more prominent, but the first statistical studies of real value to the epidemiologist were made in the epidemic of thirty years ago. Statistical study must begin with this last epidemic. Observations of the earlier epidemics, while very interesting for reference and comparison, are no longer acceptable as unquestioned statements of fact. Even at the present time and with all of the emphasis that is now being laid upon statistical procedure the records are far from perfect, and it is to be hoped that in years to come the improvement will be so decided that the records even of the 1918–20 epidemics will appear crude.
Buoninsegni remarks of the 1387 epidemic that many individuals of all ages died, but the deaths were particularly prevalent among the aged.
Jacob, of Königshofen, writes that “there came a general pestilence in the whole country, with cough and influenza, so that hardly one among ten remained healthy,” and that old and debilitated persons were frequently the victims.
Balioanus tells us that the epidemic of 1404 let not rank, age nor sex escape its effect.
In 1557, according to Valleriola, the disease appeared with pestilential rapidity, and spared neither sex, nor any age, nor rank, neither children nor old persons, rich nor poor, but that it was not as a general rule dangerous; children only, who could not freely cough out the phlegm, dying.
The same story is told by Molineux, for 1693, “All conditions of persons were attacked, those residing in the country as well as those in the city; those who lived in the fresh air and those who kept to their rooms; those who were very strong and hardy were taken in the same manner as the weak and spoiled; men, women and children, persons of all ranks and stations in life, the youngest as well as the oldest.” Molineux, however, added that, “it rather favored the very old who seldom were attacked with it.”
These observations are but broad generalizations; if we pause to study the psychology of the historian we are tempted to conclude that his primary object was to impress his readers with an idea of the enormousness of the dissemination of the disease during his period. That being the main endeavor, a tendency to exaggerate for the sake of rhetoric and yet remain within the limits of truth may be considered excusable. But during the 1889–93 epidemic there was ample opportunity to compare the estimates made by the practising physicians with the later statistical tabulations. As a rule the former were higher both as regards morbidity and mortality.