Flu (Influenza): Causes, Symptoms, Types & Treatment

Overview

What is the flu (influenza)?

Influenza, commonly referred to as the flu, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and can lead to hospitalization and death in severe cases.

When is flu season?

Flu season typically ranges from fall to early spring, with peak activity generally occurring in the winter months.

How common is the flu?

The flu is a common illness, affecting millions of individuals worldwide annually.

What is the difference between the flu and the common cold?

The flu and the common cold are both respiratory illnesses but are caused by different viruses. Flu symptoms are generally more severe and come on more suddenly than those of a common cold.

How do I know if I have the flu or COVID-19?

Flu and COVID-19 share many symptoms, making them difficult to differentiate without testing. It’s important to get tested if you exhibit symptoms of respiratory illness.

Who is at higher risk for complications from the flu?

People at higher risk include young children, the elderly, pregnant women, and those with chronic health conditions or weakened immune systems.

Symptoms and Causes

What are the symptoms of the flu?

Symptoms typically include fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and sometimes vomiting and diarrhea, mainly in children.

What causes the flu?

The flu is caused by influenza viruses affecting the nose, throat, and lungs.

Is the flu contagious?

Yes, the flu is highly contagious. It can spread to others up to about 6 feet away, mainly by microscopic droplets expelled into the air when people with the flu cough, sneeze, or talk.

How does the flu spread?

The flu virus can spread to others through the air and by touching surfaces or objects contaminated with the virus, and then touching the mouth, nose, or possibly the eyes.

How long after exposure will I get the flu?

Symptoms can appear 1 to 4 days after exposure to the virus.

Types of Influenza Viruses

Different strains of the flu virus

Influenza viruses are categorized into three main types: Influenza A, Influenza B, and Influenza C. Influenza A and B viruses cause the seasonal epidemics of disease almost every winter in the United States. Influenza C causes mild respiratory illness and is not responsible for epidemics.

Influenza A subtypes and B lineages

Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). Similarly, Influenza B viruses are divided into lineages. Understanding these can help in the formulation of the flu vaccine each year.

Diagnosis and Tests

How is the flu diagnosed?

Diagnosis usually involves a review of symptoms and may include specific tests for influenza, especially if the flu is widespread in the community or if the individual is at high risk of complications.

Management and Treatment

How is the flu treated?

Flu treatment may involve rest, plenty of fluids, and medications to relieve symptoms. Antiviral drugs can be prescribed to shorten the duration of the flu and to prevent complications, particularly for those at higher risk.

What medications treat the flu?

Antiviral drugs such as oseltamivir (Tamiflu) and zanamivir (Relenza) can treat the flu, ideally starting within 48 hours of the onset of symptoms.

Side effects of treatment

Antiviral medications can cause mild side effects like nausea and vomiting.

How do I manage symptoms of the flu?

Symptom management includes staying hydrated, resting, and using over-the-counter medications to relieve fever and aches.

Prevention

How can I prevent the flu?

The most effective way to prevent the flu is through annual vaccination. Other preventive measures include good hand hygiene and avoiding close contact with sick individuals.

Outlook / Prognosis

What can I expect if I have the flu?

Most people recover from the flu within a couple of weeks. However, some may develop complications, such as pneumonia, which can be serious and even life-threatening.

How long does the flu last?

The flu typically lasts for about one to two weeks.

How long is the flu contagious?

People with the flu are most contagious in the first 3-4 days after their illness begins, but they can spread the virus before symptoms are present and up to 7 days after becoming sick.

When can I go back to work/school?

It’s recommended to stay home for at least 24 hours after the fever is gone without the use of fever-reducing medication, except to get medical care or other necessities.

Complications

How many people die from the flu each year?

Estimated flu-related deaths vary annually, but tens of thousands of deaths can occur in the U.S. alone.

Living With

When should I see my healthcare provider?

If you are at high risk of flu complications or experience severe symptoms, it’s important to see a healthcare provider.

When should I go to the ER?

Immediate medical care is needed for severe symptoms such as difficulty breathing, chest pain, dizziness, confusion, or severe vomiting.

What questions should I ask my doctor?

Questions to ask might include the recommended treatment, signs of complications, and when it’s safe to return to daily activities.

Additional Common Questions

Is the stomach flu influenza?

No, the “stomach flu” refers to illnesses caused by other viruses, bacteria, or parasites and is not related to influenza.