As much of my city is currently shut down and the majority of us are attempting some form of social distancing to help flatten the curve of infection, I thought it would be interesting to look at an account of the epidemic of 1918 that appeared fairly soon thereafter — these excerpts are from the 12th edition Encyclopædia Britannica (1922) article on Influenza. I had to look a number of words up, not being a medical person, so here are some quick definitions: catarrh is the excessive buildup and discharge of mucus in the nose or throat due to inflammation of the mucous membranes therein. Pyrexia refers to a fever. Toxaemia is blood poisoning, and anoxaemia is an extreme reduction of the amount of oxygen in the blood.

Under the conditions of existence that prevail in the civilized communities of to-day, the human respiratory tract must necessarily encounter a large variety of pathogenic bacteria and a great deal of irritating particulate matter. Such exposure is inevitable in factories, schools, trains, 'buses and, indeed, in all forms of social intercourse within confined spaces. Under these circumstances it is not to be wondered at that acute catarrhal affections of the respiratory mucous membranes, accompanied by pyrexia, should be common. To such affections the name "influenza" is frequently applied; and it is this loose employment of the word that is responsible for much of the confusion that exists in statistical records.

The explosive pandemic of influenza that burst upon the world in 1918 was something quite different from the sporadic pyrexial catarrhs above referred to, although the individual clinical picture, when uncomplicated, was much the same. In the absence of exact knowledge of the causative agent and in view of the fact that the individual clinical picture is such as may follow many different bacterial invasions, it is impossible, at present, to formulate a completely satisfactory definition. Here the term "influenza" will be used to imply "a pandemic outburst of disease characterized, clinically, by a rapid course, catarrh of the respiratory tract, pyrexia, and some degree of prostration; and, epidemiologically, by a tendancy to occur in several successive waves at short intervals of time." [...] Statistical records of influenza mortality are apt to be very misleading as medical men often apply this name to fatal respiratory diseases of indeterminate symptomatology. When the real influenza comes, the public is at once aware of the fact because nearly everyone either gets infected or sees friends or relations infected within a very short space of time.

The Influenza Pandemic of 1918-9. — This pandemic swept over the world in three successive waves, the first appearing quite suddenly in May and June 1918, the second starting at the end of Sept. or early in Oct. and waning in Dec., and the third wave, less uniform in character, appeared early in March 1919.

First Wave. — This outbreak, attributed by France to Spain, by Spain to France and by America to eastern Europe, seems to have appeared almost simultaneously amongst the nations of the "Entente" arrayed against the enemy on the western front, and amongst all those communities in intimate touch with them. In the armies of the Entente in France, Belgium, and Italy; in the military camps in England and America; in the civilian populations of England, France, Italy, Spain, and Portugal; in transports at sea; in the closely linked theatres of war of Salonika and Egypt, and in Gibraltar, Malta, and India itself, the outbreak of influenza showed the explosive character that is only possible for a highly invasive infection assisted by conditions of swift inter-communication, such as obtain in modern war.

[...] The first wave passed rapidly, so that a "frequency curve" by weeks, in which the incidence in the worst week is taken as 100%, shows a steep ascent to a maximum, followed by an equally steep and almost symmetrical fall, the whole episode passing within about five or six weeks. So benign was the type that many cases among soldiers at the battle-front escaped record, as the men never "reported sick" but merely rested for a day or so in their units, and this was fortunate as the army hospitals were soon overcrowded. The death-rate was inconsiderable, but there was an ominous tendency to a higher mortality rate amongst the later cases, just before the wave came to an end, seeming to suggest an increase in virulence. The clinical picture cannot be better summed up than in the words of a consultant physician in France who, describing the first batch of cases, exclaimed "it is like a mild attack of measles without a rash." Respiratory catarrh, congested conjunctivæ, headache, lassitude, pyrexia of short duration, a feeling of prostration with the return of temperature to normal, and then a rapid recovery of health; such was the course in the vast majority of cases during the first wave. Complications were almost unknown during this outbreak; but a few cases developed broncho-pneumonia or hæmorrhagic œdema of the lungs towards the end of the wave, and it was these cases that sent up the case-mortality. In all these characters, the first wave closely resembled the outbreak of 1890. In one respect it showed an interesting difference. Whereas in 1890 the death-rate was greatest amongst the middle-aged and elderly, in 1918 the chief sufferers were amongst the "young adult" groups.

Second Wave. — Towards the end of Sept., or early in Oct., the second wave suddenly gathered force and swept over the world; the crowning tragedy of so many tragic years. Soldiers, miraculously spared in battle and for whom hope was now dawning with the promise of victory; youths at school or college, to whom the future might look to fill the gaps of war in years of peace: these were the harvest chosen for the scythe of the Angel of Death. For the character of the pandemic had changed and the benign attacks of the summer now gave place to the terrible scourge of the autumn outbreak. Geographically, this wave was almost universally felt, and it seemed to mount up simultaneously throughout the world. St. Helena is said to have escaped. Mauritius, too, had a reprieve; and it appears to be true that the quarantine measures applied by Australia were successful for the moment, but throughout Europe, America, Asia and Africa, this fatal pandemic held undisputed sway.

The upward curve of morbidity was almost precisely similar to that of the summer and the maximum was reached as quickly as in the previous wave, but the fall was much slower and less regular. The outstanding difference between the two waves was the marked tendency to pulmonary complications and the high death-rate of the second. The singularly uniform syndrome of the summer epidemic gave place, in the autumn, to several varieties of clinical picture depending on varying combinations of several factors, amongst which might be reckoned the virulence of the microbic invader, the resistance of the patient, the nature of the bacterial flora of his respiratory tract, and environmental conditions such as occupation, wages and housing. As a rule, the attack was ushered in by the catarrhal and pyrexial symptoms noted in May and June. In many cases, especially where circumstances permitted of immediate rest and treatment, the disease took a favourable course towards recovery, although prostration was nearly always a more marked feature than in the summer. In others, the story was different. The early pyrexial catarrh was sometimes followed by intense toxaemia leading so rapidly to a fatal issue that there was no time for pulmonary complications to develop. But in a very large number of cases the lungs became severely affected and the patient passed into a state of anoxaemia recalling that produced by exposure to the "pulmonary irritants" of gas warfare. But there was a formidable difference between the two conditions. While the "phosgene" patient had to deal with a sterile exudate, evoked by a chemical irritant and capable of rapid absorption if vitality was maintained, the lungs of the influenza patient were charged with an exudate evoked by a living virus which had already overcome tissue resistance and could offer to "secondary invaders" conditions of symbiosis favourable to their growth. Here lay the danger. The virus of influenza could open, as it were, the door to the streptococci, pneumococci, staphylococci and other organisms normally held within safe numerical limits upon the respiratory mucous membranes. [...]