Influenza

by Warren T. Vaughan

Recrudescences.

We have already seen from the work of Pearl that recrudescences following the original spread in any one locality were the rule rather than the exception in this country. He found that in sixty-five per cent. of the forty cities studied there were two distinct peaks in the mortality curve and in twenty per cent. there were three, while only fifteen per cent. had but one peak. The first peak was as a rule the highest. Although there was no absolute regularity in the time of occurrence of the recrudescences, Pearl established that the high peak cities had the second peaks on an average 7.1 weeks after the first, and the third peak on an average 13.1 weeks after the second. The two-peak cities are divided into two classes, the first comprising about a third of the total number, had the second mortality peak around eight weeks after the first, while the remaining two-thirds had the second peak about thirteen weeks after the first. The cycle in the epidemic wave appears to be nearly a multiple of seven weeks. He suggests that the smaller group of two-peak cities with early second peak may have been cities which at the time were presumably destined to show a third distinct wave and peak of mortality, but in which for some reason not now apparent the third wave did not eventuate. In contradistinction the larger group of two-peak cities with the second peak occurring around thirteen weeks after the first are presumably cities in which the complex of factors determining the form of the mortality curve was such as to lead definitely to a two and only two-peak curve. In three-peak cities the first interval was around seven weeks, the second around thirteen weeks. The two-peak cities with an interval around thirteen were probably not destined, according to Pearl, to have another repetition, but those with an interval of seven were presumably destined to have a second interval, the thirteen-week interval, which for some reason did not occur.

This raises the question of periodicity, a subject which we will discuss at a more appropriate place.

This experience of recrudescences was similar in the American Expeditionary Forces. The first outbreak lasted through April and May and into June. The second came in September and October. The spring epidemic had been characterized by mildness and was known as three-day fever, but in the autumn, complications of the respiratory tract predominated in the symptom complex. By August 18th a severe epidemic had occurred in an artillery camp at La Valdahon in the Jura Mountains, near Bezançon. Early in September a larger epidemic occurred in an artillery camp near Bordeaux. The epidemic in our troops in France, as well as in the French civil and military population, reached its height during October. The Service of Supply was more heavily affected than were the troops situated on the battle front. The morbidity rate appeared to have been almost the same as that in the United States. That it was not quite as high has been shown by Howard and Love. Longcope states that it prevailed particularly among the troops at the base ports where during a part of the epidemic transports laden with infected troops were being landed; in those organizations which contained the largest number of replacement troops; and in organizations being moved on troop trains, where the men were necessarily closely crowded.

The second outbreak subsided during the early part of November. A third occurred in January and February, very much as it had done in the United States. In the interval between the second and third recurrences there was no time at which the entire Expeditionary Forces were free from the disease. The author had occasion to study an outbreak occurring early in December in the 26th Division stationed in rest area at Montigny-le-Roi. In this outbreak the respiratory complications predominated, as in October, and the mortality was comparatively high. We had had occasion to study the same disease at Camp Sevier, South Carolina in September and early October, 1918, and in two different localities in France in December, 1918, and February, 1919, and found that the clinical characteristics were identical on both continents.

The more severe recurrence in England, in October, has been carefully studied. In fact this recurrence was almost universal in all countries. The autumn epidemic has been reported as being at its height in October, 1918, in such widely separated localities as the United States, England, France, Greece, Brazil, India, Japan and Korea.

In Europe at any rate the third wave occurring in the winter of 1919 was quite generally distributed. At about the same time the disease broke out in England, making a third wave in less than a year. Once again the third attack began less suddenly and less violently and resulted in a lower number of fatalities. During February there was reported to have been a great increase in the number of cases in Paris. It had terminated by March 27, 1919. In March the disease broke out anew, this time assuming grave proportions, not only in that city but in several of the Departments.

The second recrudescence has also been reported as being present in Spain.

On May 5, 1919, report was received from Buenos Ayres that in one of the concentration zones for naval troops located in the harbor there had been an epidemic of short duration, but with high morbidity, with two hundred cases being frequently reported each day.

Just as Pearl has observed a certain periodic recrudescence in the United States, there has been described a similar periodicity in England. The interval, however, is described as twelve weeks. The first wave began in July and died down about the end of August, running a two months course. Twelve weeks after the commencement of the first wave, at the beginning of October, the second appeared. It had disappeared around the middle of December. Again, twelve weeks from the beginning of the second wave, that is, in January, the third appeared.