The ongoing devastation of World War I engulfed much of Europe in spring of 1918 as soldiers - crowded onto military bases in the United States and along the Western Front in Europe - began to fall ill.
Droves of otherwise healthy young men reported to camp infirmaries with typical influenza symptoms like fever, aches and nausea, though doctors soon realized this was no ordinary flu.
Many who suffered from it developed a deadly form of pneumonia, and their lungs filled with bloody fluid. They choked on the pinkish froth as they gasped for their last breath.
The flu outbreak was shrouded in secrecy.
These terrifying early reports were kept secret. Americans had joined the fight in 1917, bringing the Allies ever closer to victory over Germany and the Central Powers by the spring of 1918.
The war had reached a turning point and neither side wanted to divulge any weakness, says Jim Higgins, a Spanish flu historian at the University of Houston-Victoria in Texas.
The Spanish king fell victim to the flu.
By May of 1918, influenza had reached the neutral nation of Spain, decimating the capital city of Madrid. Newspapers there - unfettered by any need for wartime censorship - began publishing reports of the deadly new virus.
Even the king of Spain, Alfonso XIII, became ill, helping to give the impression that the pandemic had started in Spain.
The U.S. and European media soon began calling it the ‘Spanish flu,’ though in Spain, people nicknamed the new influenza strain Soldado de Napoles or “Soldier of Naples,” after a song in a popular Spanish operetta. The hit song was so catchy it was said to spread like the flu.
“We now know that the Spanish flu didn’t start in Spain. In fact it probably started far from the Iberian Peninsula,” says Higgins. Yet the exact origins of the global pandemic remains a mystery.
Where did the Spanish flu really originate?
For many years, medical historians and epidemiologists hypothesized that the outbreak could have started at a British army base in Étaples, France, or at Fort Riley in Kansas, where the first American cases of this new strain of flu were recorded in March of 1918.
More recently, experts have proposed a third hypothesis: The Spanish flu originated somewhere in northern China in late 1917 and swiftly moved to western Europe with the 140,000 Chinese laborers the French and British governments recruited to perform manual labor to free up troops for wartime duty.
Regardless of its origins, the Spanish Flu was an unprecedented global catastrophe.
By the spring of 1919, the influenza pandemic had sickened an estimated one-third of the world’s population and may have killed as many as 50 million people, claiming more lives in a single year than either the First World War or the four-year-long Black Death bubonic plague outbreak that swept Europe and Asia in the Middle Ages.