The onset of influenza is almost always sudden, hence the early German name, "Blitzkatarrh." The disease begins with a chill, frequently with a rigor; simultaneously with this the temperature rises. Only in rare cases-according to our own statistics only in 7 per cent.-were there any prodromal symptoms of one or more days' duration, such as general malaise, debility, or coryza. Only in the mildest rudimentary form is the initial chill absent. Such cases are often indistinguishable from a simple coryza, diffuse muscular rheumatism, cephalic neuralgia, migraine, or a mild bronchial catarrh.
In some rare but very remarkable cases influenza begins suddenly, with quite abnormal symptoms. The disease may be ushered in by a deep faint, by convulsions, especially in children, by a fall with epileptiform convulsions and coma of long duration, or by a sudden terrible sensation of vertigo, on which stupor and lethargy may follow. But an influenza commencing with such alarming symptoms may run a mild, rapidly convalescing course. This occurred in one of the cases described by us, which was brought into the hospital with a diagnosis of apoplexy. At that time there was no pyrexia, but on the following day the fever was high and the usual symptoms of influenza were present. Consciousness returned at the same time, and after three clays the patient was fully convalescent. As in all acute infectious diseases (enteric fever, pneumonia, etc.), so occasionally with influenza, it happens that the disease commences with the symptoms of an acute psychosis, and, what is of special importance, without at this period any rise of temperature. The varieties of this initial delirium and initial psychosis are very manifold. We may mention: Stupor, sensations of fear with hallucinations, confusion, maniacal excitement with exaltation and restlessness, or even acute mania. Such cases were occasionally brought into the hospital with the diagnosis of acute mania, and thence, unfortunately, since there was no fever, sent to an asylum, from which, after passing through an attack of influenza, they were discharged cured a few days later. Occasionally, in alcoholic patients, the onset of influenza took the form of severe delirium tremens. We shall revert to this later. The explanation of these fulminating initial symptoms with severe nervous phenomena is obvious. They can be due to nothing else but an acute intoxication from the influenza toxins entering the circulation and affecting primarily the cerebrum.
Here, too, we may briefly allude to those exceedingly rare modes of onset of influenza in which, as cases coming under our own notice and others mentioned in literature* have shown, the disease may arise suddenly with severe gastro intestinal symptoms, with continuous vomiting, colic, and diarrhea, so that the case seems to be one of acute poisoning. In one of our cases all the symptoms pointed to a perforation of the appendix; the abdomen, as occasionally occurs at the onset, was of a board like hardness, and exceedingly tender to the slightest touch. On the third day, however, the abdominal symptoms disappeared and influenza, with all its typical symptoms, was revealed, with the later addition of pneumonia.
The duration of an attack of simple uncomplicated influenza, whatever its special clinical variety, is short-in the great majority of cases, only one or a few days.
We may confirm this universal experience, although it is hardly necessary to do so, by some quotations from statistics. Peacock reports that in the epidemic of 1847-1848 the duration of the disease among the London police averaged about three days; only in 1 per cent, of the cases was the duration over a week. In 45,100 grip patients treated in the Prussian army during 1889-1890, the average duration of the disease was five days. Among the 2415 school children of the district of Waldkirch (Baden), the duration of the disease was "accurately" ascertained, and in 15 per cent.,of the cases it was one day; in 63 per cent., two to five days; in 16 per cent., six to ten days, and only in 4 per cent, of the cases was the duration longer than ten days. Among 192 influenza patients of the prison of Minister, 41 per cent, were so slightly affected that it was not necessary for them to cease working; 34 per cent, were ill two to three days; 15 per cent., four to seven days, and 10 per cent., longer than a week. Of the 137 influenza patients of the reformatory of Minister, 70 per cent, could continue their work; 11 per cent, were ill one to three days; 10 per cent., four to seven days; and only in 9 per cent, of the cases was the duration of the disease longer than a week. Numerous similar statistics might be quoted. If we now give the statistics of the Berlin "sick clubs," which do not agree with those just mentioned, we do it mainly to prove the justice of our previous criticism of the morbidity of the "sick clubs." (See p. 566.) The results obtained by the Bureau of Vital Statistics of the city of Berlin from data supplied by the clubs, etc., show that the duration of the disease in 1 per cent, of the cases was one day; 31 per cent, of the cases, seven days; 31 per cent., fourteen days; 16 per cent., three weeks; and 20 per cent, were ill more than three weeks. The inference may be drawn from this that an enormous number of the mild cases was not recorded at all, to which point we have already called attention under Morbidity. (See p. 566.) Such statistics have much less value than those depending on estimates made by the doctors.
* Compare Friedrich, loc. cit., p. 331.
In most cases the patient is able, in a short time, to resume his usual occupation. But frequently even the mildest cases and the most simple attacks of influenza are followed by a long and tedious convalescence, complicated either by an obstinate neuralgia or an indescribable weakness and debility, by loss of energy, both bodily and mental, by depression, insomnia, or by prolonged and persistent gastric disturbances and anorexia. This difficult convalescence is usually far worse for the patient than the brief attack of influenza.