Chart showing the actual incidence of influenza in Boston by weeks and the actual incidence among the 10,000 individuals surveyed by weeks during the first three months of 1920.
Full Line—incidence in the entire city based upon reports to the Health Commissioner.
Dotted Line—incidence in the six districts surveyed.
The most comprehensive and detailed work that has been done in this line is that reported by Frost and Sydenstricker and by Frost, the first being the result of a canvass of 46,535 persons in Maryland, and the second a similar report based on a canvass of 130,033 persons in several different cities of the United States. We shall have occasion to refer to these later.
Morbidity.
There has been great actual variation in the morbidity from influenza in the various epidemics and even in different localities during single epidemics. Previous to 1889 there were no reliable statistics for the disease incidence, and subsequent to that date the records, for the reasons previously mentioned, have still been not entirely adequate.
In the history of influenza morbidity, as in that of its mortality, we must content ourselves for information prior to the nineteenth century with the very general estimates made by contemporary historians. During the last century the statistics have been more numerous and more nearly correct. As far back as the first recognized pandemic, 1510, the extremely high morbidity has been a recognized characteristic. Thomas Short in speaking of this pandemic says, “The disease ... attacked at once and raged all over Europe, not missing a family and scarce a person.”
Pasquier in 1557 spoke of the disease as common to all individuals, and Valleriola describes the widespread distribution of the epidemic throughout the whole of France during that year. It spared neither sex, age, nor rank, neither children nor aged, rich nor poor. The mortality, however, was low, “children only, dying.” Again, Thomas Short remarks, “This disease seized most countries very suddenly when it entered, catching thousands the same moment.”
Of the second pandemic, 1580, Short says, “Though all had it, few died in these countries except such as were let blood of, or had unsound viscera.”
Thomas Sydenham remarks that in the epidemic of 1675 no one escaped, whatever might be his age or temperament, and the disease ran throughout whole families at once.
Molineux recorded concerning 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.”