Where did the 1918 flu pandemic come from and What caused the Spanish Flu?

In 1918, the flu season came on a bit early, in April, but a few weeks before that 84,000 additional American troops had set out for Europe to fight the Germans, so there were more important things to worry about than the “grippe.”

That some people died during the spring was unremarkable, before there were any antibiotics, people often died of bacterial pneumonia, especially in the spring. While records show that men in close quarters, soldiers, for example, and prisoners, got the flu in large numbers, the extent of the general public’s affliction went unreported, and therefore largely unnoticed. No one was collecting statistics.

In any case, most of the men who got sick were ill for a few days and then got better. There was an odd thing about this flu in addition to its early arrival: it seemed to be affecting most severely people in their 20s and 30s, unlike the usual pattern of serious illness in the very young and the very old.

In any case, by August, the Office of the Surgeon General reported that the only serious health problem was that deaths from respiratory disease were up. It was only a slight rise, although it was odd for August, and especially odd that respiratory illness deaths were also up in Europe at exactly the same time. But the flu seemed to have faded. Unfortunately, it would return in the fall, and when it did, it would come back in a way that almost no one in the world could ignore.

In many cases, it began with a dull headache, rapidly followed by chills so severe that nothing could keep the patients warm. The fever led to delirium. Patients began coughing up blood, and their faces turned purple. Saliva pink with blood bubbled from their mouths as their lungs filled with fluid. Finally they died, essentially drowning, gasping for air. All this could happen in a few days or as little as a few hours.

In others, death took longer. For these people, the fever lasted four or five days, at which point bacteria invaded their damaged lungs, bringing death from bacterial pneumonia. It was like no flu before or since.

By the time it was over, an estimated 20 to 25 million people worldwide were dead from the virus. And the most terrifying part was that this flu, unlike any other, killed people in their prime as well as infants and the elderly. Adults between 20 and 40 were among the most susceptible age groups: 40 percent of the American navy and 36 percent of the army came down with the disease. In all, 28 percent of Americans were afflicted, and 675,000 of them were dead by March 1919.

This flu killed with a relentlessness and rapidity unequaled by any plague in history. (Mortality figures are complicated by many factors, and deaths from a given disease must necessarily be an estimate. There were no serology tests for the flu virus in 1918.)

Doctors in 1918 had the foresight to preserve tissue samples from flu victims, and these samples have now been analyzed using modern laboratory techniques. In one experiment, the virus was reproduced in tissue culture and injected into mice.

Although it did not have the same devastating effect on the mice that it had on humans, its viral RNA has been sequenced, showing consistency with an H1N1 influenza A virus that belongs to a subgroup that infects humans and pigs. The pandemic of 1918, in other words, may have been a kind of “swine flu.”