What To Know About Influenza A

In October 2024, about 91.4% of all confirmed flu cases were caused by influenza A. You'll likely have symptoms that affect your nose, throat, and lungs—such as fever, cough, fatigue, chills, and body aches. Influenza A is typically not dangerous. Infants, young children, and adults older than 65 are most at risk for severe flu symptoms.

The difference between influenza A and B, another type of flu virus, is that A is typically more common and severe. Influenza A often goes away on its own with hydration, rest, and home remedies. Seven to 10 days is typically how long influenza A symptoms last.

Influenza A Symptoms

Everyone experiences flu symptoms a little differently. Symptoms can last anywhere from a week to 10 days. Your symptoms may linger for a longer period or be more severe if you are younger than 18 or older than 65 and have an underlying condition or autoimmune disorder.

Common Symptoms

Influenza A primarily affects your respiratory system—which includes your nose, throat, and lungs. Symptoms can come on suddenly and may include:

• Body or muscle aches
• Cough
• Diarrhea
• Fatigue
• Fever or chills
• Headaches
• Nausea or vomiting
• Photophobia, or a sensitivity to bright lights
• Runny or stuffy nose
• Sore throat

Severe Symptoms

Influenza A can cause an additional set of symptoms in severe cases. These symptoms are rare but may sometimes become a medical emergency:

• Hypotension, or low blood pressure
• Shortness of breath or difficulty breathing
• Tachycardia, or a rapid and racing heart rate

Causes

Influenza A can happen when the virus infects the tissues in your upper respiratory tract (sinuses, mouth, and throat) or your lower respiratory tract (lungs). The virus can replicate within these tissues, which causes symptoms.

This type of flu is highly contagious. You can transmit the virus to someone else by coughing, sneezing, or speaking near them. You can also contract the virus if someone who is sick passes their germs to you when they cough, sneeze, or talk.

This type of flu virus often mutates (changes) rapidly every flu season. Your immune system might not be able to fight off newer forms of the virus right away, even if you have had the flu before. You may have symptoms for a few days as your immune system fights the infection.

Risk Factors

Anyone can develop influenza A. Certain people are at greater risk for severe symptoms and complications, such as:

• Adults older than 65
• Infants and children younger than 2
• Pregnant people
• People who have chronic conditions like heart, kidney, or liver disease
• Those who have a weak immune system, such as from an autoimmune disorder, cancer, chemotherapy, or steroids
  

Diagnosis

Healthcare providers mainly rely on a physical exam and health history to diagnose you with influenza A. These assessments are enough for a proper diagnosis during flu season, which typically peaks between December and February.

A healthcare provider may order laboratory tests to rule out other conditions if your symptoms last for a long period. Influenza A shares symptoms with other viral infections, such as COVID-19.

Diagnostic tests include:

• Chest X-ray: Takes images of your lungs to rule out bacterial infections or pneumonia
• Immunofluorescence: Looks for the flu and other viruses using a specialized microscope to examine specimens taken from a sample of tissue from your sinuses or throat
• Polymerase chain reaction (PCR) test: Identifies flu viruses from samples of your tissue, which can take anywhere from 45 minutes to several hours to offer results
• Rapid antigen test: Detects the presence of a virus after collecting a sample of your tissue from your nose or throat, which can show results in as quickly as 15 minutes
• Rapid molecular assay for nucleic acid detection: Delivers results within 15 to 30 minutes after getting a sample of your tissue from a swab test to identify viruses

Treatments for Influenza A

Getting enough rest and drinking more fluids can help your body fight off influenza A without additional medical treatment. Antiviral drugs are available if your symptoms are not going away or feel severe. These medications attack viruses and prevent transmitting the illness to others.

Healthcare providers recommend starting antiviral drugs within two days of symptom onset. They can reduce the duration of the illness and the severity of your symptoms.

A healthcare provider may prescribe the following drugs to ease symptoms:

• Relenza Diskhaler (zanamivir)
• Tamiflu (oseltamivir)

Prevention

It's easy to catch influenza A during flu season because the illness is so contagious. Prevention strategies can protect you from the flu or reduce your risk of complications if you do get sick.

Some prevention methods include:

• Avoiding touching your face as germs can easily spread from your hands to your eyes, nose, or mouth
• Covering your mouth with the crook of your elbow or a tissue when you sneeze or cough
• Disinfecting and cleaning surfaces or objects that may have come into contact with someone who has the flu
• Getting an annual flu shot
• Limiting contact with people who have the flu
• Washing your hands regularly and thoroughly
• Wearing a high-quality mask

Complications

Most cases of influenza A resolve within a couple of weeks. The flu can be more severe and lead to complications in some people.

Complications may include:

• Ear infection: The immune response to influenza A causes inflammation, which can affect and cause fluid to build up in the eustachian tube. This tube connects the back of your throat to your middle ear. The fluid attracts bacteria that may cause an ear infection.
• Encephalitis: The immune response may cause this inflammation of the brain. Influenza A may also affect the central nervous system.
• Myocarditis: The immune response can also affect the heart muscle. Myocarditis is inflammation of the heart muscle, which may cause chest pain and trouble breathing.
• Myositis: An overactive immune response to the flu can cause inflammation of the muscles. Symptoms include painful, tender, and weak muscles.
• Pneumonia: Influenza A can weaken your immune system, making you more susceptible to bacteria that cause a secondary infection. Pneumonia, which affects the lungs, is a common secondary infection in people with the flu.
• Sepsis: This is a severe, life-threatening reaction to an infection. It occurs if germs enter the bloodstream. Sepsis can cause organ damage and death if it's untreated.
• Sinus infection: Influenza A may cause congestion and inflammation of the sinuses, which attracts bacteria that can cause an infection.

A Quick Review

Influenza A is the most common type of flu virus that causes seasonal epidemics of the flu during the colder months. This illness is highly contagious and causes symptoms like fever, cough, nasal congestion, and fatigue.

Many cases of influenza A resolve on their own with proper rest. Antiviral drugs can reduce the duration of illness and prevent complications. Getting vaccinated, washing your hands, and limiting contact with someone who has the flu can reduce your risk of developing the flu.