The flu (influenza) is a seasonal respiratory illness that comes on suddenly, most often with fever, body aches and a dry cough.
Flu season spans as early as October and can last as late as May, peaking between December and February.
There is some variety in how the flu presents itself, depending on a person's age and their general state of health, although many symptoms are commonly observed.
Symptoms of the flu
Typical signs and symptoms of the flu include:
Fever: an increase in body temperature is almost always present with the flu. The fever can be low grade, in the 100°F (37.8°C) range, or as high as 104°F (40°C). Young children tend to have higher temperatures and can even reach 106°F (41.1°C). Some individuals may describe feeling feverish and chilled at the same time. The fever may last up to a week.
Influenza is characterized by fever, cough, fatigue and body aches among other symptoms.
Cough: the initial cough with the flu is non-productive (dry), persistent and often painful. The cough may be mild initially, but tends to worsen as the infection evolves. A feeling of breathlessness or discomfort with breathing is common. The cough can linger for two weeks or more.
Headache: the headache is usually severe and tends to be over the forehead and behind the eyes. It may be accompanied by additional eye symptoms such as sensitivity to light, redness, tearing and a burning sensation.
Chills: the shaking and feeling of coldness occur because of the fever.
Muscle aches and joint pain: aches and pains range from mild to severe are common in the back, arms and legs.
Malaise: malaise is a general feeling of discomfort, illness, uneasiness - an overall lack of well-being. Appetite is also diminished or lacking altogether (anorexia). This is a common complaint with many illnesses and is often the first indication of an infection.
Sore throat: the sore throat may be severe and typically lasts 3-5 days.
Weakness and fatigue: weakness and fatigue can be so severe that they interfere with normal activities such as work and school. People who have the flu cannot seem to get enough sleep and are completely exhausted; even getting up to use the bathroom can seem like a challenge.
Runny or stuffy nose: nasal congestion and sneezing are seen more often with the common cold, but some individuals may get nasal symptoms such as these with the flu.
Vomiting and diarrhea: these symptoms are rarely seen in adults with the flu, but vomiting and/or diarrhea occur in 10-20% of flu infections in children.
How long do flu symptoms last?
The majority of people recover from the flu in 3-5 days, although the feeling of malaise may last for a week or longer.
However, the flu can become complicated by pneumonia, a serious infection of the lung that requires treatment and, in some individuals, hospitalization. Older adult patients, young children and those with preexisting medical conditions are more prone to developing pneumonia.
Sometimes it can be challenging to know if your symptoms are from the flu or another form of illness. The flu can look a lot like other viral respiratory infections, and symptoms can be vaguer in the older and younger populations.
You may not even suspect your symptoms are from the flu if you have had a flu shot. Unfortunately, the flu shot is not 100% effective against the flu.
In 2015, a report from the Centers for Disease Control and Prevention (CDC) stated that the flu vaccine for that flu season was only 23% effective. This low level of efficacy was attributed to a large number of "drift variants" - viral strains of influenza with antigenic or genetic changes that made them different from the viruses used in the vaccine.
In summary, some of the hallmark signs and symptoms of the flu are:
- Sudden onset: you know exactly when flu hits you, and it is within 2 days of your exposure to the virus.
- A longer duration of fever: fevers with other viral respiratory infections only last 1-2 days.
- Significant body aches: everything seems to hurt, even your hair. If it is hard to get out of bed and if it feels like you were "hit by a truck," the illness is likely to be the flu.
- Flu season: it is unusual to see the flu in the warm summer months.
- You do not have vomiting and diarrhea: the flu is a respiratory illness. Children are an exception, however, as they may have gastrointestinal symptoms.
The majority of people recover from the flu within a week. However, there are certain groups of people for whom the flu can be life-threatening. If you think you have the flu, talk to your medical provider.
There is a rapid flu test that can be done in the office to help confirm if your symptoms are from the flu. There are also prescription antiviral medications available that, if started during the first 48 hours of the flu's onset, can help lessen the severity and course of the infection.
Learn more about influenza, including how it is caused, treated and prevented.
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