Stomach Bug: Viral or Bacterial, Rehydrating Right and When Not to Use Loperamide

At a glance

What is it? An infection of the stomach and gut with diarrhea, often also nausea and vomiting.
Cause Mostly viruses (for example norovirus), more rarely bacteria.
The most important thing Drink enough to make up for the fluid loss.
Usually Over on its own after a few days.
Caution Antibiotics and anti-diarrheals are often not needed and sometimes harmful.
ICD-10 A09 (infectious gastroenteritis)

Contents

  1. What is a stomach bug?
  2. Symptoms and course
  3. Norovirus or bacteria? The difference
  4. The most important thing: fluids and electrolytes
  5. When not to use loperamide or an antibiotic
  6. Avoiding infection
  7. When to see a doctor

What is a stomach bug?

A stomach bug (medically acute gastroenteritis) is an infection of the stomach and gut. Typical signs are diarrhea, often together with nausea, vomiting and abdominal cramps. It is usually caused by viruses, above all noroviruses, more rarely by bacteria and only rarely by parasites.

Stomach bugs are very common and in the vast majority of cases harmless. They usually settle on their own after a few days. The most important task during this time is not a particular medicine but drinking enough, because the biggest danger is the loss of fluid.

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Symptoms and course

A stomach bug often starts suddenly. Typical symptoms are:

  • diarrhea, often watery. More on this: Diarrhea.
  • nausea and vomiting. More on this: Nausea.
  • abdominal cramps and stomach pain.
  • sometimes fever, headache and aching limbs, and exhaustion.

A stomach bug usually settles on its own after a few days. With a norovirus, things often improve after just one to three days. The biggest danger is not the infection itself but the loss of fluid, especially in small children and older people.

Norovirus or bacteria? The difference

Most stomach bugs are viral. Sometimes, though, bacteria are behind it, and that can matter for treatment. It can only be told for certain with a stool test, but there are some clues:

More likely viral (e.g. norovirus) More likely bacterial (e.g. Campylobacter, Salmonella)
Stool watery diarrhea, usually without blood sometimes bloody or mucousy diarrhea
Vomiting often prominent (especially norovirus) diarrhea more in the foreground
Fever usually no or only mild fever more often high fever
Duration usually short, often 1 to 3 days sometimes longer and more severe
Source very contagious from person to person often via food (poultry, eggs), sometimes after travel

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The boundaries are blurred, and the symptoms alone cannot tell for certain what the cause is. What matters above all: with bloody diarrhea, high fever or a severe, longer-lasting course, you should seek medical advice, and then a stool test can make sense.

The most important thing: fluids and electrolytes

With a stomach bug, the most important thing is not a particular medicine but drinking enough. Through diarrhea and vomiting, the body loses fluid and salts (electrolytes), and making up for exactly that is the central treatment.

  • drink plenty, ideally in small sips spread over the day.
  • an oral rehydration solution from the pharmacy is ideal, especially with greater losses, in small children and in older people. It replaces fluid and salts in the right ratio.
  • water, diluted juices and clear broth are also suitable. Very sugary drinks on their own are less good, as they can worsen the diarrhea.
  • eat as your appetite allows, as soon as you can, ideally light food. Strict fasting is not necessary. Breastfed babies continue to be breastfed.

Keep an eye on whether enough is being drunk and passed. When a lack of fluid becomes dangerous is described below in the section "When to see a doctor".

When not to use loperamide or an antibiotic

Many people reach for a medicine that stops the diarrhea, or hope for an antibiotic. Both are often not sensible and can even be harmful.

Loperamide (anti-diarrheal). In adults with watery diarrhea without blood and without high fever, loperamide can be used briefly for relief, for example when you have to get through the day. But it only treats the symptom, not the cause. Keep away from it with bloody diarrhea or high fever, because then it can be harmful. In small children, loperamide should not be given. More on the active substance: Loperamide.

Antibiotics. Most stomach bugs are caused by viruses, against which antibiotics do not help at all. But many bacterial infections also heal on their own in otherwise healthy people, without an antibiotic. Antibiotics are only used in certain cases, for example with severe courses or in people with a weakened immune system, and that is decided by a doctor. Unnecessary antibiotics can have side effects, promote resistance and, with certain pathogens (for example EHEC), even favour dangerous complications.

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Avoiding infection

Stomach bugs, especially noroviruses, are very contagious. This is how you lower the risk of infecting yourself or others:

  • wash your hands thoroughly with soap, above all after using the toilet and before eating.
  • with an infection in the household, use your own towels and clean surfaces, the toilet and door handles.
  • anyone who is ill should as far as possible not prepare food for others and not work with food, until at least two days after the symptoms have settled.
  • cook food well, especially poultry, and pay attention to kitchen hygiene.

When to see a doctor

See a doctor if the diarrhea is bloody, high fever is added, the symptoms do not get better after several days or are very severe, or if you have recently been in a high-risk area abroad. You should be especially careful with small children, older or frail people, during pregnancy and with chronic illnesses, where early medical advice is worthwhile.

Have signs of severe fluid loss assessed at once Get medical help quickly or call the emergency number (112, in the US: 911) if signs of severe dehydration appear: hardly any urine, sunken eyes, severe weakness, confusion or circulation problems, or if nothing at all can be kept down (persistent vomiting). In babies and small children, warning signs include a dry diaper for many hours, sunken eyes and unusual drowsiness or unresponsiveness, and here every hour counts. Bloody diarrhea with high fever or very severe, persistent abdominal pain should also be assessed by a doctor quickly.

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  • Intake reminders: for your other medicines, which should not be forgotten now.
  • Medication plan: all medicines in one place, ready for the next appointment.
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Frequently asked questions

Usually only a few days. With a norovirus, things often improve after just one to three days. Some bacterial infections last a bit longer. If the symptoms persist over several days or get worse, you should seek medical advice.

Ideally plenty, in small sips, best an oral rehydration solution from the pharmacy. Water, diluted juices and clear broth are also suitable. Very sugary drinks on their own are less good.

In adults with watery diarrhea without blood and without high fever, loperamide can give brief relief. With bloody diarrhea, high fever and in small children it should not be used, as it can be harmful.

Usually not. Most stomach bugs are viral, so antibiotics do not help. Many bacterial infections also heal on their own. Antibiotics are only prescribed by a doctor in certain cases.

Only for certain with a stool test. Roughly: a viral infection tends to be watery diarrhea with vomiting, short and without blood. Bacterial tends to be bloody diarrhea, high fever or a longer, more severe course. With these signs, see a doctor.

With bloody diarrhea, high fever, severe or multi-day symptoms, signs of dehydration and with risk groups such as small children, older people or pregnant women. With severe dehydration, at once.

Wash your hands thoroughly, use your own towels, clean surfaces and, while ill, do not prepare food for others, until at least two days after the symptoms have settled.

Eat as your appetite allows, as soon as you can, ideally light food. Strict fasting is not necessary. What matters most is drinking enough.

Related topics

Diarrhea Loperamide Nausea Vomiting Abdominal pain

Quellen

  1. DGVS (Deutsche Gesellschaft für Gastroenterologie) u. a.: S2k-Leitlinie „Gastrointestinale Infektionen“ (AWMF 021-024, Version 2.0, 2023). register.awmf.org/de/leitlinien/detail/021-024
  2. GPGE: S2k-Leitlinie „Akute infektiöse Gastroenteritis im Säuglings-, Kindes- und Jugendalter“ (AWMF 068-003). register.awmf.org/de/leitlinien/detail/068-003
  3. Robert Koch-Institut (RKI): Ratgeber Norovirus-Gastroenteritis, Campylobacter, Salmonellose, EHEC. rki.de
  4. IQWiG / gesundheitsinformation.de: Magen-Darm-Infekt und Durchfall. gesundheitsinformation.de
  5. BZgA: infektionsschutz.de, Magen-Darm-Infektionen. infektionsschutz.de
Important note: This article is for general information and does not replace medical advice, diagnosis or treatment. With signs of severe dehydration, persistent vomiting, bloody diarrhea with high fever or in affected babies and small children, you should seek medical help promptly. Last updated: June 2026.