“The flux” is an old medical term for dysentery, a severe intestinal infection that causes bloody diarrhea, intense abdominal cramping, and mucus in the stool. The term was widely used from the 1600s through the 1800s, and you’ll most often encounter it in historical accounts of wars, slave ships, and colonial settlements. Eighteenth-century physicians gave it descriptive names like “bloody flux,” “obstinate flux,” and “violent flux” depending on how severe or persistent the illness was.
What the Flux Actually Was
Flux referred to the uncontrolled, frequent discharge of bloody stool that defined the illness. Physicians of the era described symptoms lasting over two weeks: excrement “mixed with flimsy sharp matter” that caused “severe gripping pains,” frequent blood in the bowels, and vomiting. In modern medicine, these symptoms fall squarely under the diagnosis of dysentery, which is still very much a real disease today.
Dysentery comes in two main forms. Bacillary dysentery is caused by bacteria, most commonly Shigella, but also Salmonella, Campylobacter, and certain strains of E. coli. Amoebic dysentery is caused by a parasite called Entamoeba histolytica. Both types produce similar symptoms, but the bacterial form tends to come on faster and more aggressively, while the parasitic form can linger for weeks or months if untreated.
Why It Killed So Many People
The flux was likely the leading cause of death among enslaved captives on Atlantic slave ships. It devastated military camps, colonial towns, and anywhere large groups of people lived in close quarters with poor sanitation. The disease spreads through the fecal-oral route: germs from an infected person’s stool get into food, water, or onto surfaces, and another person swallows them. On a crowded ship or in a camp with no clean water and no sewage system, this cycle was nearly impossible to break.
What made the flux so deadly in earlier centuries wasn’t just the infection itself. The real killer was dehydration. Constant bloody diarrhea drains the body of fluid and electrolytes faster than most people could replace them, especially without access to clean drinking water. Before the development of oral rehydration therapy and antibiotics, there was little anyone could do once the disease took hold.
Symptoms in Modern Terms
If someone develops dysentery today, the core symptoms are the same ones historical doctors described. The hallmark is frequent, small-volume stools containing visible blood and mucus, often accompanied by fever, severe abdominal cramps or tenderness, and an urgent, painful need to use the bathroom. This differs from ordinary food poisoning or stomach flu, which typically produces large-volume watery diarrhea without blood.
The World Health Organization defines diarrhea as three or more loose stools in 24 hours, but dysentery is a distinct and more serious pattern. It’s the blood and mucus that set it apart and signal that the lining of the intestine is being actively damaged by the infection.
How It’s Treated Today
Most cases of Shigella infection, the most common bacterial cause, resolve on their own within five to seven days with rest and fluids. Mild cases don’t require antibiotics. For severe cases, doctors can prescribe antibiotics after testing to confirm which drugs will work, since some strains of Shigella have developed resistance to certain medications.
One important note: common anti-diarrheal medications like loperamide (Imodium) should not be used during a Shigella infection. These drugs slow gut movement, which can actually make the illness worse by keeping the bacteria trapped in the intestines longer. The body’s diarrhea response, as miserable as it is, helps flush the infection out.
Serious Complications
In rare cases, certain strains of E. coli that cause dysentery can trigger a condition called hemolytic uremic syndrome, where toxins from the bacteria damage red blood cells and the kidneys. This complication can lead to kidney failure, permanent health problems, and in some cases death. Most people who develop it recover within a few weeks with hospital care, but it remains one of the most dangerous outcomes of a severe gut infection. Children and older adults face the highest risk.
Prevention Is Still About Hygiene
The same conditions that made the flux so devastating on 18th-century ships still drive dysentery outbreaks today: contaminated water, poor sanitation, and inadequate handwashing. The disease remains common in parts of the world where clean water infrastructure is limited, and travelers to these regions are at increased risk.
The most effective prevention is thorough handwashing with soap and water, particularly after using the bathroom, before preparing or eating food, and after changing diapers. Washing raw fruits and vegetables with safe water before eating them, avoiding uncooked foods in areas with questionable water supplies, and staying out of swimming pools while sick with diarrhea all help break the transmission cycle. These measures sound simple, but they address exactly the fecal-oral pathway that spreads the infection.