Salmonella typically causes loose, watery diarrhea that can range from greenish to yellow-brown, and in some cases contains visible mucus or streaks of blood. Symptoms usually start 6 hours to 6 days after eating contaminated food and last 4 to 7 days, though diarrhea specifically can persist for up to 10 days.
If you’re staring into the toilet trying to figure out whether salmonella is the cause, here’s what to look for and how it compares to other common stomach bugs.
Color, Consistency, and Smell
The hallmark of salmonella infection is frequent, watery diarrhea. Stools are typically loose and unformed, often with a notably foul smell. The color can shift depending on how quickly food is moving through your intestines. When the gut is severely inflamed and everything is passing through rapidly, bile doesn’t have time to break down fully, which can give stool a greenish or yellow-green tint. As the infection progresses, stools may become more yellow-brown or remain watery and pale.
Mucus in the stool is common. Your intestinal lining produces extra mucus as part of its inflammatory response to the bacteria. You might notice it as a slimy coating or stringy strands mixed in with the liquid stool. Some people also see small streaks or flecks of blood, which happens when the rapid onset of diarrhea disrupts the intestinal lining enough to cause minor bleeding. Bloody diarrhea doesn’t happen in every case, but it’s not unusual either.
The volume and frequency are often what catch people off guard. You may have multiple watery bowel movements per hour during the worst of it, and the stool is mostly liquid rather than formed. It can feel more like passing water than passing a normal bowel movement.
Why Salmonella Causes This Type of Diarrhea
Salmonella bacteria don’t just pass through your gut passively. They actively invade the cells lining your intestines using specialized molecular tools that inject proteins into your gut tissue. Once the bacteria reach a critical density, your immune system launches a strong inflammatory response. Your body floods the intestinal lining with immune cells and signaling molecules, which triggers the gut to secrete large amounts of fluid into the intestinal space. That fluid is what produces the watery diarrhea.
This is actually your body’s defense mechanism. The flood of fluid is designed to flush the bacteria out. But it also means you’re losing water and electrolytes rapidly, which is why dehydration is the main risk of a salmonella infection rather than the bacteria themselves.
How It Differs From a Stomach Virus
Salmonella diarrhea and viral gastroenteritis (the “stomach flu”) look very similar in the toilet, which makes them hard to tell apart on stool appearance alone. Both cause watery diarrhea that can occasionally be bloody. Both come with nausea, vomiting, and cramping. But there are a few patterns that can help you distinguish them.
Timing is the biggest clue. Salmonella from contaminated food often hits within 2 to 6 hours of eating, though it can take up to 6 days. Viral gastroenteritis from norovirus or similar bugs typically has a 24 to 48 hour incubation period. If your symptoms came on fast after a specific meal, food-borne salmonella is more likely.
Duration also differs. Viral gastroenteritis generally resolves within about 2 days. Salmonella symptoms last 4 to 7 days on average, and diarrhea can linger for up to 10 days. It may take several months for your bowel habits to fully return to normal. Fever and chills tend to be more prominent with viral infections, though salmonella can cause fever too, so this isn’t a reliable way to tell them apart.
What the Stool Can’t Tell You
There is no stool appearance that definitively confirms salmonella. Green, watery, mucus-filled diarrhea can also come from other bacterial infections like E. coli or Campylobacter, or from non-infectious causes like food intolerances. The only way to confirm salmonella is through a lab test. A stool culture is the gold standard for diagnosis, and the CDC recommends it whenever salmonella is suspected, particularly if antibiotics might be needed.
Most healthy adults recover from salmonella without treatment. The infection runs its course in about a week, and the main priority during that time is replacing fluids and electrolytes lost through diarrhea. Oral rehydration solutions, broth, and water are more important than trying to eat solid food while symptoms are active.
Signs the Infection Is More Serious
Certain stool changes suggest the infection is hitting harder than a typical case. Persistent bright red blood or large amounts of blood in the stool indicate more significant intestinal damage. Diarrhea that continues beyond 10 days, or that’s so frequent you can’t keep fluids down, raises the risk of dangerous dehydration.
Watch for signs that fluid loss is outpacing what you can drink: dark urine or very little urine output, dizziness when standing, dry mouth, and a rapid heartbeat. Children, older adults, and people with weakened immune systems are at higher risk of salmonella spreading beyond the gut into the bloodstream, which is a more serious condition that requires medical treatment. A fever above 102°F (39°C) that lasts more than a couple of days can be a signal that the infection isn’t staying contained to the intestines.