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Symptoms and Signs of Flu in Adults

Doctor's Notes on Flu in Adults

Flu, or influenza, is an upper respiratory infection caused by influenza viruses. There are many different types of influenza viruses, so it is possible to develop the disease multiple times. The viral infection is contagious and people acquire the infection from contact with infected people or objects.

Signs and symptoms of a mild case of the flu may resemble those of a severe cold and can include runny or stuffy nose, cough, sneezing, fatigue, malaise, and headache. With influenza, fever is more likely to occur, and it may be high. Other possible associated symptoms can include weight loss, loss of appetite, weakness, nausea, vomiting, diarrhea, and sore throat. If vomiting or diarrhea are present, symptoms of dehydration may develop.

Medical Author:
Medically Reviewed on 3/11/2019

Flu in Adults Symptoms

Flu symptoms and signs usually come on suddenly. The onset of illness includes the following:

  • Fever (usually high)
  • Severe aches and pains in the joints and muscles (especially in the back) and around the eyes
  • Generalized weakness
  • Ill appearance with warm, flushed skin and red, watery eyes
  • Headache
  • Dry cough
  • Sore throat and watery discharge from the nose or nasal congestion
  • Vomiting or diarrhea sometimes occurs, particularly in children

Flu in Adults Causes

Four types of influenza viruses exist. Types A and B cause epidemics of severe respiratory illnesses known as "the flu," and type C causes a mild illness not associated with epidemics. Type D does not cause human disease. Type A has two different subtypes or strains, based on the chemical structure of the virus. The H1N1 swine flu virus is a type A influenza virus. Type B is not divided into subtypes. Both type A and type B are responsible for the seasonal influenza outbreaks.

  • Outbreaks occur more frequently in the winter months. Many factors may play a role in this seasonal pattern:
    • The virus survives for longer periods indoors in winter because the relative humidity of indoor air is very low in comparison to the outside air.
    • The virus is in droplets that are coughed or sneezed; it infects others via inhalation or by landing on sensitive body areas such as the eyes, nose, or mouth. These droplets generally travel no further than 6 feet.
    • In the winter, humans tend to be indoors more and thus have closer contact with each other, which makes it easier for the virus to spread.
  • Health officials may classify flu outbreaks as epidemics (occurring in a set geographical area) or pandemics (a worldwide occurrence). A flu pandemic can occur when a new influenza A virus emerges against which there is very little immunity already in the human population. Because there is little immunity, the new virus can spread from person to person very easily and can sicken more people. In 2009, a pandemic influenza strain began circulating called "novel" H1N1 influenza or swine flu (also referred to as "A(H1N1)pdm09" or "2009H1N1").
  • Influenza is a contagious disease. The virus is spread when you either inhale infected droplets in the air (spread when an infected person coughs or sneezes) or when you come in direct contact with an infected person's secretions (for example, by kissing, sharing of handkerchiefs and other items, and through use of objects such as spoons and forks). Flu virus survives on surfaces for up to 48 hours. Touching surfaces, such as doorknobs, elevator buttons, keyboards, and phones, are other ways to transfer the virus to your hands, which may then contact the nose, mouth, or eyes, where the virus gets absorbed.
  • A sudden increase in the number of school-aged children sick at home with flu-like illness may indicate the arrival of flu season. Similar infections in other age groups, especially among adults, soon follow this outbreak.

Home Remedies for the Flu or a Cold Slideshow

Home Remedies for the Flu or a Cold Slideshow

Caring for a sick child brings extra stress and worry for everyone in the family—especially parents. Unfortunately, colds and the flu are very common in children. On average, kids can expect five or six colds a year before they start school. Some kids get as many as eight to 10 colds a year. It isn’t until they become teenagers that kids settle down to adult levels of cold infections, getting infected about four times a year on average.

Kids get sick a lot because they’ve never been exposed to the many common cold and flu viruses that most adults have already built immunities to. Building immunities takes time: many years, in fact. Plus there are more than 200 different cold viruses, making the situation worse.

Unfortunately colds cannot be cured. That’s why treatment is your first line of defense when it comes to fighting sickness in children. In this article, we will use the advice of medical experts to give you the best chances of easing your child’s cold and flu symptoms.

Fighting Cold Symptoms: Why Rest Is Best

Sleep is restorative, and it helps us recover from illness. This is why it's important for your children to rest when they are under the weather. Keep them home from school or daycare if they are sick, especially if they have a fever. This will also help keep the germs from spreading to classmates.

  • Try to give them at least 8-10 hours of sleep.
  • Let them rest until they feel better.
  • One study indicated that the less sleep we get, the more likely we are to become infected after being exposed to a cold virus.

Even if your children do not sleep, it's a good idea to limit their activity and keep them resting. Let them stay in bed and read them their favorite book or watch a movie.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.