Salmonella is a bacterial infection that attacks the lining of your intestines, triggering inflammation, watery diarrhea, and stomach cramps that typically last four to seven days. Most healthy adults recover without treatment, but in roughly 8% of confirmed cases, the bacteria escape the gut and spread to the blood, bones, or other organs, where the infection becomes far more serious.
How Salmonella Gets Inside Your Cells
Salmonella doesn’t just sit on the surface of your intestines. It actively breaks in. The bacteria use a needle-like structure to inject specialized proteins directly into the cells lining your small intestine. These proteins hijack the cell’s own machinery, essentially tricking it into pulling the bacteria inside. The primary targets are M cells, specialized gateway cells that sit above clusters of immune tissue called Peyer’s patches in the intestinal wall.
Once inside, Salmonella doesn’t die the way most swallowed bacteria would. It survives within immune cells called macrophages, the very cells your body sends to destroy it. This is what makes the infection so effective: the bacteria use your own defense system as a vehicle, riding inside macrophages to potentially reach the liver, spleen, and bloodstream.
The number of bacteria needed to cause illness is surprisingly small. For a typical foodborne Salmonella infection, swallowing around 1,000 organisms can be enough. People with reduced stomach acid, weakened immune systems, or advanced age can get sick from even fewer.
What Happens in Your Gut
The hallmark symptoms of salmonellosis, diarrhea and cramping, aren’t caused by the bacteria themselves destroying tissue. They’re caused by your immune system’s aggressive response to the invasion. Once Salmonella breaches intestinal cells, those cells release chemical alarm signals that recruit waves of immune cells called neutrophils from the bloodstream into the intestinal wall. These neutrophils then push through the intestinal lining into the gut itself, disrupting the barrier in the process.
At the same time, bacterial proteins interfere with how your intestinal cells handle chloride, a salt that controls water balance. The result is a flood of fluid into your intestines, producing the watery diarrhea that defines the illness. Some of the bacterial proteins also trigger the release of inflammatory molecules like TNF-alpha, which ramps up swelling, increases blood flow to the area, and recruits still more immune cells. This cascade is why the cramping can be severe: your gut is swollen, leaking fluid, and under full immunological assault.
The diarrhea sometimes contains blood or mucus, a sign that the inflammatory response has damaged the intestinal lining itself.
Symptoms and Timeline
Symptoms typically appear 6 hours to 6 days after eating contaminated food, with most people noticing something wrong within 12 to 36 hours. The core symptoms are watery diarrhea and stomach cramps. Many people also experience nausea, vomiting, headache, and loss of appetite. Fever is common, usually low-grade but sometimes reaching 102°F or higher.
For most people, the worst of it passes in four to seven days. The diarrhea usually resolves first, while fatigue and reduced appetite can linger for a week or two beyond that. One thing worth knowing: you can continue shedding Salmonella in your stool for weeks after you feel better, which is why hand hygiene matters even after recovery.
When Salmonella Spreads Beyond the Gut
In about 8% of lab-confirmed cases, Salmonella doesn’t stay confined to the intestines. It enters the bloodstream or lodges in other organs, creating what doctors call an invasive infection. The most common forms include bacteremia (bacteria circulating in the blood), bone infections, joint infections, and in rare cases, meningitis.
This is far more likely in three groups: young children (especially under 5), adults over 65, and people with compromised immune systems, including those on immunosuppressive medications, people with HIV, or those undergoing chemotherapy. In these populations, the infection can progress to sepsis, organ failure, and death if untreated.
Healthy adults almost never face this level of danger. Their immune systems contain the bacteria within the gut, clear the infection, and build some short-term immunity in the process.
Long-Term Effects
Even after the infection clears, a small percentage of people develop reactive arthritis, an inflammatory joint condition triggered not by the bacteria themselves but by the immune response they provoked. This typically shows up days to weeks after the gastrointestinal symptoms resolve. Studies estimate that anywhere from 0% to 15% of people develop reactive arthritis following Salmonella and similar gut infections, with the wide range reflecting differences in genetics, severity, and how the cases were tracked.
Reactive arthritis usually affects large joints like knees and ankles, causing pain, swelling, and stiffness. It can also involve inflammation in the eyes or urinary tract. Most cases resolve within a few months, though some people experience recurring flares.
How It’s Diagnosed
If your symptoms are severe enough to warrant testing, a stool sample is the standard starting point. The traditional method, growing the bacteria in a lab culture, remains the gold standard with very high accuracy, but it takes one to three days for results. Many labs now use rapid molecular tests (PCR-based panels) as a first-line screen. These return results in hours and are highly specific, meaning a positive result is very reliable, but they miss some cases that culture would catch, with sensitivity around 85 to 95% depending on the test.
Most mild cases never get formally diagnosed. People assume they had “food poisoning,” ride it out, and recover without ever confirming which bacteria was responsible.
Treatment and Recovery
Most people recover without antibiotics. The primary concern during a Salmonella infection is dehydration from fluid loss, so the main treatment is replacing fluids and electrolytes, whether through oral rehydration solutions or simply drinking water, broth, and electrolyte drinks consistently throughout the day.
Antibiotics are reserved for severe intestinal infections and for people at high risk of the bacteria spreading beyond the gut. Using antibiotics for mild cases doesn’t speed recovery and can actually prolong the period during which you shed the bacteria, potentially extending how long you’re contagious. For invasive infections that reach the blood or other organs, antibiotics become essential and are typically given in a clinical setting.