The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses.

The flu is caused by flu viruses that spread from person to person. When someone with the flu coughs, sneezes, or talks, they spray tiny droplets. These droplets can land in the mouths or noses of people who are nearby. Less often, a person may get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

Symptoms of the flu come on suddenly and may include:

• Fever or feeling feverish/chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue (tiredness)

Some people may also have vomiting and diarrhea. This is more common in children.

Sometimes people have trouble figuring out whether they have a cold or the flu. There are differences between them:

Sometimes people say that they have a "flu" when they really have something else. For example, "stomach flu" isn't the flu; it's gastroenteritis.

Some people who get the flu will develop complications. Some of these complications can be serious or even life-threatening. They include:

• Bronchitis
• Ear infection
• Sinus infection
• Pneumonia
• Inflammation of the heart (myocarditis), brain (encephalitis), or muscle tissues (myositis, rhabdomyolysis)

The flu also can make chronic health problems worse. For example, people with asthma may have asthma attacks while they have flu.

Certain people are more likely to have complications from the flu, including:

• Adults 65 and older
• Pregnant women
• Children younger than 5
• People with certain chronic health conditions, such as asthma, diabetes, and heart disease

To diagnose the flu, health care providers will first do a medical history and ask about your symptoms. There are several tests for the flu. For the tests, your provider will swipe the inside of your nose or the back of your throat with a swab. Then the swab will be tested for the flu virus.

Some tests are quick and give results in 15-20 minutes. But these tests are not as accurate as other flu tests. These other tests can give you the results in one hour or several hours.

Most people with the flu recover on their own without medical care. People with mild cases of the flu should stay home and avoid contact with others, except to get medical care.

But if you have symptoms of flu and are in a high risk group or are very sick or worried about your illness, contact your health care provider. You might need antiviral medicines to treat your flu. Antiviral medicines can make the illness milder and shorten the time you are sick. They also can prevent serious flu complications. They usually work best when you start taking them within 2 days of getting sick.

The best way to prevent the flu is to get a flu vaccine every year. But it's also important to have good health habits like covering your cough and washing your hands often. This can help stop the spread of germs and prevent the flu.

Centers for Disease Control and Prevention

Your gallbladder is a pear-shaped organ under your liver. It stores bile, a fluid made by your liver to digest fat. As your stomach and intestines digest food, your gallbladder releases bile through a tube called the common bile duct. The duct connects your gallbladder and liver to your small intestine.

Your gallbladder is most likely to give you trouble if something blocks the flow of bile through the bile ducts. That is usually a gallstone. Gallstones form when substances in bile harden. Gallstone attacks usually happen after you eat. Signs of a gallstone attack may include nausea, vomiting, or pain in the abdomen, back, or just under the right arm.

Gallstones are most common among older adults, women, overweight people, Native Americans and Mexican Americans.

Gallstones are often found during imaging tests for other health conditions. If you do not have symptoms, you usually do not need treatment. The most common treatment is removal of the gallbladder. Fortunately, you can live without a gallbladder. Bile has other ways to reach your small intestine.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

Gangrene is the death of tissues in your body. It happens when a part of your body loses its blood supply. Gangrene can happen on the surface of the body, such as on the skin, or inside the body, in muscles or organs. Causes include:

• Serious injuries
• Problems with blood circulation, such as atherosclerosis and peripheral arterial disease
• Diabetes

Skin symptoms may include a blue or black color, pain, numbness, and sores that produce a foul-smelling discharge. If the gangrene is internal, you may run a fever and feel unwell, and the area may be swollen and painful.

Gangrene is a serious condition. It needs immediate attention. Treatment includes surgery, antibiotics, and oxygen therapy. In severe cases an amputation may be necessary.

Everyone has gas. Most people pass gas 13 to 21 times a day. Passing gas through the mouth is called belching or burping. Passing gas through the anus is called flatulence. Most of the time gas does not have an odor. The odor comes from bacteria in the large intestine that release small amounts of gases that contain sulfur.

Gas in the digestive tract comes from two sources: air that you swallow and the breakdown of undigested food by bacteria in the large intestine. Certain foods may cause gas. Foods that produce gas in one person may not cause gas in another.

You can reduce the amount of gas you have by:

• Drinking lots of water and non-fizzy drinks
• Eating more slowly so you swallow less air when you eat
• Avoiding milk products if you have lactose intolerance

Medicines can help reduce gas or the pain and bloating caused by gas. If your symptoms still bother you, see your health care provider.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

Gastroenteritis is an inflammation of the lining of the stomach and intestines. The main symptoms include vomiting and diarrhea. It is usually not serious in healthy people, but it can sometimes lead to dehydration or cause severe symptoms.

There can be many different causes of gastroenteritis:

• Viruses
• Bacteria
• Parasites
• Chemicals
• Reactions to certain medicines and food

Viral gastroenteritis is the most common type. It can be caused by many different viruses, including noroviruses and rotaviruses. Some people call viral gastroenteritis the "stomach flu." But this name is not medically correct. It is not caused by flu viruses. The flu is a respiratory infection that affects your nose, throat and lungs.

When gastroenteritis is caused by consuming foods or drinks contaminated with viruses, bacteria, parasites, or chemicals, this is called food poisoning.

The viruses, bacteria, and parasites that cause gastroenteritis can also spread from person to person. You could be infected when you touch something that has the germs on it and then touch your eyes, mouth, or nose.

The symptoms of gastroenteritis include:

• Diarrhea
• Pain or cramping in your abdomen (belly)
• Nausea
• Vomiting
• Sometimes fever

Gastroenteritis is usually not serious. But it can sometimes cause lead to dehydration or cause severe symptoms. Certain people are at higher risk for these problems. They include:

• Pregnant women
• Older adults
• People with weakened immune systems or other serious health conditions
• Infants
• Babies who were born prematurely or have other health conditions

If you or a family member are at higher risk and have symptoms of gastroenteritis, contact a health care provider right away. Even if you are not at high risk, it is possible to become dehydrated or have more serious symptoms. There are some warning signs to watch for. It's important to contact a provider right away if you or your child have any of them:

• For adults, they include:
  • Change in mental state, such as irritability or lack of energy
  • Diarrhea lasting more than 2 days
  • High fever
  • Vomiting often
  • Six or more loose stools in a day
  • Severe pain in the abdomen (belly) or rectum
  • Stools that are black and tarry or contain blood or pus
  • Symptoms of dehydration, such as thirst, dry mouth, headache, dark-colored urine, and urinating less than normal
• For infants and children, they include:
  • Change in the child's mental state, such as irritability or lack of energy
  • Diarrhea lasting more than a day
  • Any fever in infants
  • High fever in older children
  • Frequent loose stools
  • Vomiting often
  • Severe pain in the abdomen (belly) or rectum
  • Signs or symptoms of dehydration, such as thirst, dry mouth, urinating less than usual or no wet diapers for 3 hours or more, and no tears when crying
  • Stools that are black and tarry or contain blood or pus

To find out if you have gastroenteritis, your provider:

• Will do a physical exam
• Will ask about your symptoms
• May do tests of your stool

Usually, people with gastroenteritis get better on their own, with rest and plenty of fluids and electrolytes. Your provider may suggest that you take a probiotic. Studies suggest that some probiotics may help shorten a case of diarrhea.

People with more severe symptoms may need medicines to control nausea or vomiting. Providers may also give other medicines for certain types of gastroenteritis, such as antibiotics for some bacterial types and antiparasitic medicines for some parasitic types.

Gastroenteritis cannot always be prevented. But proper hand washing, cleaning surfaces that may be infected with germs, and safe food preparation may help prevent some of the infections that can cause gastroenteritis. There are vaccines for infants to protect against rotavirus infections.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases