In discussing the recrudescence of influenza in Boston in November and December, Woodward remarks as follows:
“Whether or not it may be more than a succession of coincidences it is certainly of interest to note that the November outbreak of influenza showed itself three days after the Peace Day celebration on November 12th, when the streets, eating places and public conveyances were jammed with crowds; that the December epidemic began to manifest itself after the Thanksgiving holiday, with its family re-unions and visiting; and that reported cases mounted rapidly during the period of Christmas shopping, reaching a maximum a week after the holiday.” That this may have been a coincidence is indicated by the fact that, according to reports by Pearl and others this was not consistently true in other large cities.
Dr. Meredith Davies records the case of a hostel in Wales accommodating 200 students. Infection was introduced on October 19th on the occasion of a dance attended by some students from an infected institution in the neighborhood. Four cases occurred on the 20th and within the short space of five days seventy-nine students out of the 200 were attacked.
Parsons found numerous similar examples in the epidemic of 1889. In 1918 it was frequently observed that among American Soldiers in France, those troops quartered in barracks suffered a much more rapid spread of the disease than those billetted out among the houses of the towns.
Mass attack.—Another argument formerly raised against the contagious character was the claim that it broke out in mass attack, and large numbers became ill on the same day without the occurrence of isolated antecedent cases. The first cases of such epidemic diseases as the plague and small pox became a matter of record because of the accompanying high mortality, while in influenza, with its relatively low death rate the record usually begins only after a comparatively large mass of individuals have been attacked.
Watson in 1847 observed as follows: “Although the general descent of the malady is, as I have said, very sudden and diffused, scattered cases of it, like the first droppings of a thunder shower, have usually been remembered as having preceded it. The disorder is most violent at the commencement of the visitation; then its severity abates; and the epidemic is mostly over in about six weeks. Yet the morbific influence would seem to have a longer duration. In a given place nearly all the inhabitants who are susceptible of the distemper suffer it within that period, or become proof against its power. But strangers, who, after that period, arrive from uninfected places have not, apparently, the same immunity.”
Parkes in 1876 observed that, “When the disease enters a town it has occasionally attacked numbers of the inhabitants almost simultaneously. But more frequently its course is somewhat slower; it attacks a few families first and then in a few days rapidly spreads; the accounts of thousands of persons being at once attacked at the onset of the disease are chiefly taken from the older records, in which the suddenness of the outbreak is exaggerated. Frequently, perhaps always, in a great city the outbreak is made up by a number of localized attacks, certain streets or districts being more affected than others, or being for a time solely affected, and in this way it successively passes to different parts of the city. It has generally occurred in a great city before appearing in the smaller towns and villages round it and sometimes these towns, though in the neighborhood, have not been invaded for some weeks.
“In some cases and perhaps a large number, it breaks out after persons ill with influenza have arrived from infected places.
“The decline in any great town is less rapid than its rise, and usually occupies from four to six weeks, or sometimes longer.”
Detailed studies of the Munich epidemic of 1889 and numerous similar studies of the recent epidemic, which will be referred to later, have shown a period of two or three weeks of steadily increasing numbers of cases before the height of the epidemic was reached.