Is the Stomach Flu Contagious?

Stomach flu or gastroenteritis is a general term for a number of inflammatory problems that occur in the gastrointestinal tract. Gastroenteritis is a better term because when some individuals use the term "stomach flu," they get the term confused with the flu (influenza) and the viruses that cause the flu. Influenza viruses do not cause stomach flu.

The most common symptoms of the stomach flu include:

• Diarrhea
• Nausea
• Vomiting
• Abdominal pain

Other symptoms may include:

• Fever
• Headache
• Body aches
• Dehydration

Because stomach flu means gastroenteritis and, because when the term “stomach flu” is used, the readers usually mean acute gastroenteritis caused by viruses (mainly Norovirus); the emphasis of this article will be on Norovirus-caused gastroenteritis although other causes will be mentioned.

There are many causes of stomach flu. The most common cause is contagious gastroenteritis which can be due to:

• Viruses (for example, Norovirus, Adenovirus and others)
• Bacteria (for example, Salmonella, Shigella, E. coli and others)
• Parasites (for example Giardia lamblia, Cryptosporidium, and others)

However, many other causes of gastroenteritis that are not contagious include:

• Food allergies
• Antibiotics
• Toxins

Many medications also list gastroenteritis as a common side effect.

The primary symptoma of stomach flu or gastroenteritis include:

• Diarrhea that typically does not contain blood
• Nausea
• Occasional vomiting
• Abdominal cramping

The incubation time for gastroenteritis varies according to the particular cause. The most rapid incubation time is usually with viral illnesses (for example, for Norovirus, which is about 1-2 days), and the infected person may become contagious during this time without symptoms of nausea or diarrhea.

Noncontagious causes (allergies, toxins, medication side effects) may produce symptoms very rapidly (minutes to hours) and in some people, the symptoms may become so severe that they require emergency care.

Doctors usually base the diagnosis on the person's history and physical exam; some patients will need further blood and fecal tests done to determine the cause, especially in more severe infections.

Stomach flu typically spreads in the following ways:

• Contagious cases of stomach flu (gastroenteritis) are spread usually through contamination of food or water or by person-to-person (fecal-oral route) spread via contaminated droplets containing infectious organisms.
• Some contagious cases of gastroenteritis (most notably, Norovirus) can be spread by kissing and other close personal contact or on surfaces where droplets containing viruses or other agents survive.
• Some viruses can even be spread to household pets such as dogs that, in turn, can spread the disease to other people.

Fortunately, most causes of contagious gastroenteritis are not spread by breastfeeding or through breast milk. Noncontagious gastroenteritis such as that related to side effects of medicine or food allergies is not spread from person to person.

Stomach flu is contagious when the organisms that cause stomach flu are spread to uninfected individuals. The timeframe or how long the infected person remains contagious depends on the infecting cause. For example, most common cause of stomach flu is Norovirus. It has an incubation period of about 12-48 hours, and can cause the person to be contagious during the incubation period and for as long as they shed virus (usually about 3 days after symptoms stop but sometimes up to 2 weeks). Norovirus symptoms usually last about1-2 days and is sometimes called the 24-hour stomach flu.

Other infectious agents such as other viral strains, bacteria, and other infectious agents have incubation periods and contagious periods unique to them. Because this is an introductory article about stomach flu, readers are recommended to check the incubation periods and contagious periods of whatever infectious agent is thought to be causing the problem (for example, Salmonella or E. coli).

For contagious causes of stomach flu, many individuals have symptoms that last about 2 to 5 days, after which the symptoms tend to resolve. Once the symptoms resolve, an individual may be considered "cured" of stomach flu. However, it's not unusual for that same individual to develop stomach flu again at some point in time if they are exposed to other causes, or in some individuals, the same infectious cause. Occasionally, the stomach flu "symptoms" progress and goes on to become another more severe disease (for example, salmonellosis or shigellosis).

The most common cause of stomach flu, noroviruses, can live on surfaces for up to about 2 weeks. Therefore, is important to try to avoid contaminating surfaces while you are infected with the virus. Equally important, anyone not infected individual should wash their hands with soap and water after touching surfaces that might be contaminated. Cleaning surfaces like doorknobs or kitchen counters with a diluted bleach and water solution can help reduce the chance of infection.

For other causes of stomach flu (gastroenteritis), the reader is suggested to look up the specific infectious agent to determine how long it will remain viable and contagious on surfaces.

Many people get contagious stomach flu from different causes, but in general, they recover from the infection in about 2 to 5 days and usually do not contact a health care professional. Most doctors consider gastroenteritis to be a self-limiting disease. Unfortunately some people, especially the elderly, young children, and individuals that have multiple medical problems may develop more severe symptoms. Consequently, people should contact their health care professional or emergency department if one or more in the following cases:

• Gastroenteritis symptoms that last more than 5 days
• Worsened intensity of symptoms
• Fever above 101 F or 38.3 C
• Bloody diarrhea
• Signs of dehydration such as little or no urine output or dry mucous membranes
• Constant or increasing abdominal pains
• Person is immunocompromised, has other medical problems, or is pregnant
• Facial or throat swelling
• Shortness of breath