Spanish flu

The 1918–1920 flu pandemic, also known as the Great Influenza epidemic or by the common misnomer Spanish flu, was an exceptionally deadly global influenza pandemic caused by the H1N1 subtype of the influenza A virus. The earliest documented case was March 1918 in Haskell County, Kansas, United States, with further cases recorded in France, Germany and the United Kingdom in April. Two years later, nearly a third of the global population, or an estimated 500 million people, had been infected. Estimates of deaths range from 17 million to 50 million, and possibly as high as 100 million, making it the deadliest pandemic in history.

The pandemic broke out near the end of World War I, when wartime censors in the belligerent countries suppressed bad news to maintain morale, but newspapers freely reported the outbreak in neutral Spain, creating a false impression of Spain as the epicenter and leading to the "Spanish flu" misnomer. Limited historical epidemiological data make the pandemic's geographic origin indeterminate, with competing hypotheses on the initial spread.

Most influenza outbreaks disproportionately kill the young and old, but this pandemic had unusually high mortality for young adults. Scientists offer several explanations for the high mortality, including a six-year climate anomaly affecting migration of disease vectors with increased likelihood of spread through bodies of water. However, the claim that young adults had a high mortality during the pandemic has been contested. Malnourishment, overcrowded medical camps and hospitals, and poor hygiene, exacerbated by the war, promoted bacterial superinfection, killing most of the victims after a typically prolonged death bed.

This pandemic was known by many different names depending on place, time, and context. The etymology of alternative names historicises the scourge and its effects on people who would only learn years later that viruses caused influenza. The lack of scientific answers led the Sierra Leone Weekly News (Freetown) to suggest a biblical framing in July 1918, using an interrogative from Exodus 16 in ancient Hebrew: "One thing is for certain—the doctors are at present flabbergasted; and we suggest that rather than calling the disease influenza they should for the present until they have it in hand, say Man hu—'What is it?'"

Outbreaks of influenza-like illness were documented in 1916–17 at British military hospitals in Étaples, France, and just across the English Channel at Aldershot, England. Clinical indications in common with the 1918 pandemic included rapid symptom progression to a "dusky" heliotrope face. This characteristic blue-violet cyanosis in expiring patients led to the name 'purple death'.

The Aldershot physicians later wrote in The Lancet, "the influenza pneumococcal purulent bronchitis we and others described in 1916 and 1917 is fundamentally the same condition as the influenza of this present pandemic." This "purulent bronchitis" is not yet linked to the same A/H1N1 virus, but it may be a precursor.

In 1918, 'epidemic influenza', also known at the time as 'the grip' (French: la grippe, grasp), appeared in Kansas, U.S., during late spring, and early reports from Spain began appearing on 21 May. Reports from both places called it 'three-day fever'.

Many alternative names are exonyms in the practice of making new infectious diseases seem foreign. This pattern was observed even before the 1889–1890 pandemic, also known as the 'Russian flu', when the Russians already called epidemic influenza the 'Chinese catarrh', the Germans called it the 'Russian pest', and the Italians called it the 'German disease'. These epithets were re-used in the 1918 pandemic, along with new ones.