A “stomach bug” is the common term for viral gastroenteritis – a viral infection of the stomach and intestines. It causes inflammation of the gut lining and leads to symptoms like nausea, vomiting, and watery diarrhea. People often call it the “stomach flu,” but it has nothing to do with influenza (the true flu attacks the respiratory tract, not the gut). Viral gastroenteritis usually spreads easily from person to person or by eating/drinking something contaminated with the virus. There is no specific medication that “cures” the virus; most healthy people recover with rest and fluids.

In contrast, food poisoning generally refers to illness from contaminated food (usually bacteria or their toxins, though viruses and parasites can also be involved). Food poisoning typically comes on suddenly after eating spoiled or unclean food. Its symptoms – stomach cramps, nausea, vomiting, diarrhea – are very similar to a stomach bug, so it can be hard to tell them apart by symptoms alone. The difference lies in the cause: stomach bugs are caused by viruses, while food poisoning is often caused by bacteria like Salmonella or E. coli. (Laboratory tests on stool can distinguish viral from bacterial causes.) Treatment of both focuses on relieving symptoms and staying hydrated, but in some bacterial food poisoning a doctor may also prescribe antibiotics.

Common causes and how they spread: Stomach bugs are most often caused by viruses. The leading culprit worldwide is norovirus, a highly contagious virus that causes acute gastroenteritis. In the U.S., norovirus causes an estimated 19–21 million cases each year, making it the single largest cause of vomiting and diarrhea outbreaks. Another major cause is rotavirus, which used to be a top cause of severe diarrhea in babies and young children until routine vaccination became widespread. Other viruses – such as adenoviruses and astroviruses – also contribute, especially in young kids.

These viruses spread very easily via the fecal-oral route. Infected people shed virus particles in stool and vomit, which can contaminate food, water, surfaces, or hands. For example, a food worker with norovirus can leave the virus on salad or utensils, infecting anyone who eats it. Direct person-to-person spread is common in close quarters (day-care centers, nursing homes, schools, cruise ships). Viruses survive on surfaces and resist some cleaners, so touching a contaminated doorknob or toilet handle and then touching your mouth can infect you. Outbreaks often occur when one sick person transmits the virus to many others via shared food, drink, or close contact. Notably, WHO reports that norovirus is the most common cause of acute gastroenteritis worldwide, responsible for a huge global burden of illness and even thousands of deaths in developing countries.

Symptoms and typical duration: Stomach bugs usually begin suddenly. Common symptoms include watery diarrhea, nausea, vomiting, and stomach cramps. There may also be low-grade fever, headache or muscle aches, and a general feeling of weakness. Unlike some bacterial infections, true stomach flu usually does not cause bloody diarrhea – if you see blood, other causes should be considered. Symptoms typically appear about 1–3 days after exposure to the virus. Most people feel better in just a few days: the CDC notes that most norovirus illnesses resolve within 1–3 days, and StatPearls reports that viral gastroenteritis in developed countries usually clears up in 1–3 days. (In rare cases symptoms can last longer – up to one or two weeks – especially if dehydration occurs or if a complication arises.)

Because vomiting and diarrhea can be intense, dehydration is the biggest concern. Watch for warning signs such as very dry mouth, decreased urination (dry diapers in babies), sunken eyes, dizziness, or lethargy. The CDC specifically warns that repeated vomiting or diarrhea can quickly lead to dehydration, “especially in young children, older adults, and people with other illnesses”. Maintaining fluid balance is critical during this illness.

Treatment (home care and when to see a doctor): There is no cure for a stomach bug – treatment is supportive and focuses on hydration and comfort. For most healthy people, home care is sufficient. Begin by drinking small sips of clear fluids such as water, broths, or electrolyte-replacement drinks (e.g. oral rehydration solutions) to replace fluids and salts. Eating is often the last priority while nausea is bad; once vomiting eases, introduce bland foods (like toast, rice, bananas, or the BRAT diet) a little at a time. Avoid sugary, caffeinated, or dairy-heavy drinks initially, as these can irritate the stomach. Over-the-counter anti-nausea or anti-diarrheal medicines may help adults feel better, but they are not recommended for young children or some elderly patients. (Also, antibiotics are ineffective for viral infections and generally not used unless a bacterial cause is identified.) In otherwise healthy people, symptoms typically improve on their own with this home care. In fact, CDC and Mayo Clinic note that many people recover simply by resting and replacing lost fluids.

However, some cases require medical attention. Contact a doctor (or seek emergency care) if the patient cannot keep any fluids down for 24 hours, or if vomiting and diarrhea persist beyond 2 days. Likewise, see a doctor if there are any signs of severe dehydration (extreme thirst, very little urine output, rapid heartbeat, dizziness upon standing). Seek care if there is blood in vomit or stool, or if a high fever (above 104°F) develops. For infants and young children, call the pediatrician sooner: a child with a fever over 102°F (39°C), constant crying, or refusal to drink is concerning. Older adults and immunocompromised people with prolonged symptoms should also get prompt medical attention, as they can dehydrate very quickly. (In a healthcare setting, doctors may give IV fluids and electrolyte replacement if oral intake is not possible.)

Prevention tips (hygiene, vaccination, food safety): Preventing stomach bugs relies on good hygiene and safe food practices. Handwashing is paramount: wash hands thoroughly with soap and water after using the bathroom and before handling or eating food. (Alcohol hand sanitizers may not kill norovirus effectively, so soap and water is best.) Clean and disinfect contaminated surfaces promptly – use a bleach-containing cleaner if possible, since viruses like norovirus can cling to surfaces. During an illness outbreak or after symptoms resolve, wash soiled laundry (clothes, bedding, towels) in hot water. Food safety measures also reduce risk: cook meats and shellfish thoroughly (norovirus and some bacteria survive in raw or undercooked shellfish), refrigerate perishables promptly, and avoid cross-contamination (use separate cutting boards for raw meat). Do not share eating utensils, cups, or food with someone who is sick. Importantly, people with a stomach bug should stay home and avoid preparing food for others for at least 48 hours after symptoms end, to avoid spreading the virus to others.

Once the illness occurs, rehydration is key. If a person can drink, give small, frequent sips of water or an electrolyte solution. Pediatric electrolyte drinks or diluted sports drinks can help, but follow instructions (avoid too much sugar in little children). A healthcare provider may recommend a nasogastric or IV fluid if intake remains impossible. For symptom relief in adults, anti-diarrheal pills (like loperamide) or anti-nausea medication (like ondansetron) can be used, but again these are generally not given to young children or patients over 65 without doctor advice.

Vaccination is another preventive measure for certain stomach bugs. A safe and effective vaccine exists for rotavirus, and it is routinely given to infants in the U.S. and many other countries. CDC reports that rotavirus vaccination has dramatically reduced severe diarrhea hospitalizations in young children. (No vaccine is yet available for norovirus, though research is ongoing.)

Special considerations: Some groups need extra care when dealing with stomach bugs.

• Children: Young children and infants are at higher risk because they dehydrate faster and may not communicate how sick they feel. Parents should give small sips of fluid often and watch for signs like few wet diapers or listlessness. Infants should get the rotavirus vaccine on schedule, as it greatly reduces severe infections. See a doctor early if a baby or child has a high fever, bloody diarrhea, constant crying, extreme irritability, or very dry mouth/skin.
• Elderly: Adults over 65 can become very sick from a stomach bug. In the U.S., norovirus causes about 900 deaths each year, mostly in older adults. The elderly often have weaker immune responses and less body water to lose, so dehydration can be life-threatening. Caregivers should encourage elders to drink fluids at the first sign of illness, and consider medical care even if symptoms seem moderate. The CDC and Mayo note that older adults have much higher complication rates from gastroenteritis.
• Immunocompromised: People with weakened immune systems (due to conditions like HIV, cancer chemotherapy, or immunosuppressive medications) can have worse, more prolonged stomach bugs. They may shed virus longer and take more time to recover. Extra vigilance with hygiene is needed around these individuals, and at the first sign of gastroenteritis they may need medical support (sometimes IV fluids or hospitalization) to avoid complications.

In all cases, prevention and early hydration are crucial. By understanding what causes stomach bugs and how they spread, one can take steps (like handwashing, safe food handling, and vaccinating children) to reduce the risk. At the first signs of illness, resting and replenishing fluids usually lead to recovery in a few days. However, if symptoms are severe or don’t improve, especially in a vulnerable person, medical help should be sought promptly.