Here’s what you’ll learn when you read this story:

• In late January 1857, president-elect James Buchanan and his entourage were staying at Washington D.C.’s National Hotel when they fell ill and began spewing bloody vomit. The illness seemed to subside, but when guests flooded back to the hotel for the March inauguration, it returned with a vengeance.
• While Buchanan survived and was able to make the inauguration, dozens of people died and hundreds more were affected, leaving doctors baffled by what could possibly be causing the epidemic.
• It turned out that during the particularly harsh winter of 1857, waste, dead pests and human excrement had accumulated underground, and something emerged when the sludge thawed.

On the eve of his inauguration, James Buchanan was vomiting blood. Weeks earlier, he and his entourage had first checked into the National Hotel—the plush dreamland of Southern aristocrats—in Washington, D.C. A mysterious illness had swept through the guests then, sickening dozens before seemingly dying down. But when Buchanan and hundreds of supporters returned for the inauguration in early March, the sickness came roaring back. As they sauntered into the dining room, those in the top echelon of society were blissfully unaware of what they would later face. Buchanan’s men indulged in dinner, later planning to retire to the smoking rooms. Hundreds of them instead found themselves on their knees, vomiting along with him.

Buchanan was a northerner with southern sentiments—a staunch anti-abolitionist who defended Southern interests on slavery (to the dismay of the rest of the north), but swept electoral votes nonetheless. The country that had been paid for with blood not even a century before was slowly fracturing at the Mason-Dixon line. Unnoticed in the broader chaos, beneath its gilded facade, the National was also breaking down as the winter of 1857 receded. Pipes cracked. Rats crawled. Cesspools stagnated beneath its foundations, and the outdated city plumbing it depended on was breathing its last. Some guests, including Buchanan’s nephew and secretary Elliot Eskridge Lane, noticed a suspicious odor snaking through the hallways. Many passed it off as what remained of the musty smell of winter, and covered their noses with perfumed handkerchiefs.

But overnight, the most opulent hotel in Washington turned into a plague house. And the plague did not discriminate. From the highest of the social elite to the lowliest of servants, violent expulsions of waste became the norm. Heavy fatigue came down on the affected afterwards, making it impossible to escape. Buchanan’s cramps were so severe that he was doubled over and gasping for breath. When the new president rose to give his inauguration address the next morning, color had fled from his face and left a husk of the man he had been.

Fatalities piled up. Whatever this epidemic was, it claimed 33-year-old Eskridge Lane (whom Buchanan thought of as the son he never had) amongst nearly three dozen others. Many of the confused doctors who flocked to the hotel blamed the illness either on typhoid or some form of gastroenteritis that they could not yet diagnose. Some prescribed calomel (a mercury chloride compound meant to induce more vomiting to purge a malignant humor), but the treatment only hastened death.

Other doctors thought it was dysentery or cholera. Miasma theory, which was popular at the time, suggested that the mysterious illness may have been caused by malignant vapors snaking throughout the building. And while pointing the finger at “bad air” was barking up the wrong tree, the theory wasn’t entirely off-base, either—what miasma theory failed to account for (and that germ theory would later expose) were the viruses, bacteria, and parasites that lurked in the sources of these vapors.

Front page headlines spread almost as ruthlessly as the illness itself. Without a diagnosis, it became known as the National Hotel Disease—so lethal that people frantically crossed the street just to dodge the hotel’s shadow. Eventually, assassination theories began to emerge, and an accusatory finger was pointed at free Black Americans (though none worked in the National’s kitchen). But these theories were shut down after the realization that Buchanan’s vice president, John C. Breckenridge, was similarly sympathetic to Southern interests and unlikely to advance the abolitionist cause. Any abolitionist who wanted to eliminate Buchanan would have gained little if Breckenridge rose to power.

Whether this outbreak of illness could have been an instance of biological welfare or poison sabotage was also debated. Arsenic was easily obtainable (in the form of rat poison) just about anywhere, and with that option on the table, experts began to look for evidence. Both living patients and autopsies revealed disturbing similarities to the results of arsenic poisoning. Those who survived were left with defeated immune systems and such severe inflammation of the intestinal lining that they could barely digest anything.

The problem with this theory, however, was that some symptoms usually caused by arsenic were still missing. And with calomel (a mercury chloride mineral once used as medicine, despite causing mercury poisoning itself) only worsening the condition, doctors turned to tartar emetic, which induced even more vomiting from an already raw stomach and esophagus. Laudanum, a concoction of alcohol and opium, temporarily stopped the vomiting, but only allowed the body to absorb more toxins. And laudanum zombified the mind. In an episode straight out of a psychological horror tale, those treated with it—including Buchanan and his cabinet—turned into glassy-eyed living ghosts.

Despite their many attempts to treat the illness, doctors failed to accurately identify the true culprit: waste and human excrement that had frozen underground in the pipes and drains during the especially harsh winter of 1857, and that had begun to thaw out and infiltrate the hotel. Investigators discovered dead rats floating in the hotel’s water tank by lantern light—though the tank was used only for washing, not drinking, as the hotel’s drinking water was brought in from a distance. Arsenic, used to eliminate rats, was also found in the building. Over time, the contamination of both food and water by sewage backup from frozen plumbing meant guests were unknowingly exposed to dangerous pathogens.

The National Hotel Disease mystified the masses, and despite understanding that the cause of the outbreak was likely contamination of the water, the exact microbial culprit behind the incident was never identified. It could have been dysentery (whether it was amoebic dysentery or another type), food poisoning from shigella, or leptospirosis creeping out of the drowned rats. But the most likely cause is now thought to be typhoid, caused by the Salmonella typhi bacteria. However, with no biological samples surviving, the source of the illness may never be definitively diagnosed.