Influenza is a respiratory illness caused by different types of the influenza virus, such as influenza A (including H3N2 and H1N1) and influenza B. It affects the respiratory tract, including the nasal passages, mouth, throat, and lungs, causing symptoms like cough, runny nose, and sore throat.

Cases of influenza, also known as the flu, are often mild and get better on their own without the need for specific treatments. Children, pregnant people, and the elderly have a higher risk of experiencing severe symptoms, such as shortness of breath and rapid breathing, as well as complications from the flu. Vaccination against influenza is particularly encouraged in these groups.

It is important to contact your doctor or primary care provider if you think you might have the flu. They can help confirm a diagnosis and recommend the best treatment plan, which may include the use of certain medications. Severe symptoms like shortness of breath or difficulty breathing require immediate evaluation in the emergency department.

Online symptom checker

Report your symptoms below to determine your risk for having the flu:

Please note that this is only a guidance tool, and does not replace an assessment or diagnosis by a doctor.

Main symptoms

The most common symptoms of influenza include:

Cough and sneezing;
Sore throat;
Body aches;
Headache or pain behind the eyes;
Nasal congestion or runny nose;
Fever;
Red or watery eyes;
Malaise;
Weakness and fatigue.

In the case of mild symptoms, contact your doctor or primary care provider. They can evaluate your symptoms and arrange for the most appropriate treatment.

Serious symptoms like shortness of breath, rapid breathing or fast heartbeat, extreme fatigue, and low blood pressure require immediate evaluation in the emergency department.

How it spreads

Influenza is transmitted by infected individuals through respiratory droplets expelled from the the mouth or nose when a person coughs, sneezes, or talks. The infection spreads when these droplets land on another person and come into contact with the mucous membranes lining the mouth, nose, and eyes.

Infection can also occur when a person touches a contaminated surface and then touches their eyes, nose, or mouth. Door handles, cell phones, and another person's hands are examples of surfaces that are commonly contaminated by respiratory droplets.

Types of influenza

There are four types of the influenza virus:

Influenza A, which includes the subtypes H1N1 and H3N2, among others;
Influenza B, which includes different lineages (the Yamagata and Victoria lineages) and strains;
Influenza C;
Influenza D.

While only influenza types A and B cause infection in humans, some types of the influenza virus that normally affect animals may sometimes mutate enough to be able to be transmitted from animals to humans and from one person to another. This is the case with bird flu and swine flu, which are caused by different types of the influenza A virus.

Confirming a diagnosis

Diagnosis of the flu is often made by a doctor or other other healthcare provider based on symptoms. It is more common in the fall and winter months.

In some cases, lab tests like a rapid antigen test may be done to identify the virus and confirm a diagnosis. In these cases, a PCR test is the most reliable.

Exams like a chest X-ray may be ordered in some people to evaluate the lungs and rule out other conditions like pneumonia.

Treatment options

Treatment of influenza may involve:

Antipyretics and analgesics, such as acetaminophen and ibuprofen;
Saline nasal spray;
Home remedies with anti-inflammatory and expectorant properties, such as ginger syrup;
Antiviral medications like oseltamivir for people who are hospitalized or at increased risk for complications.

It is important to see your doctor or primary care provider for symptoms of influenza lasting more than two weeks in order to rule out complications like sinusitis or bronchitis. Seek emergency medical attention for symptoms like shortness of breath, rapid heartbeat, or low blood pressure.

Preventing the flu

Ways to help prevent the spread of the flu include:

Washing your hands frequently with soap and warm water for at least 30 seconds;
Avoiding touching your eyes, noise, and mouth;
Covering your mouth and nose when you cough or sneeze;
Avoiding crowds and poorly ventilated spaces with a lot of people, especially if you have symptoms;
Using a face mask to cover both your nose and mouth.

These are simple tips that can help prevent the spread of influenza and are especially important if you think you might have the flu. In addition, the flu vaccine (flu shot) is the best form of protection against the flu.

When to get the vaccine

The flu shot is recommended for anyone older than 6 months of age, and is especially important for children, pregnant people, and the elderly. It is usually given in the fall or at the start of winter.

Different types of the vaccine are available for those who have a contraindication to a specific type. Talk to your healthcare provider about which vaccine is right for you.