Influenza (Flu): Symptoms, Causes, Treatment, Prevention and When to Seek Help

Influenza, commonly called the flu, is a contagious respiratory infection caused by influenza viruses. It mainly affects the nose, throat and lungs and can cause symptoms such as fever, chills, cough, headache, muscle aches, tiredness and a runny or stuffy nose.

For most healthy people, influenza improves with rest, fluids and supportive care. However, the infection can sometimes become serious, particularly in older adults, young children, pregnant people and those with certain chronic health conditions and may affect to other areas of the body like heart and brain.

Begin Health Life presents this article as the understanding of flu symptoms, how influenza spreads, how it is treated and how it can be prevented can help reduce both illness and transmission.

What Is Influenza?

Influenza is a viral infection of the respiratory system. Several types of influenza viruses can infect humans, but influenza A and influenza B are responsible for most seasonal flu infections.

Influenza viruses can change over time, which is one reason seasonal flu vaccines are updated regularly. Influenza A includes different subtypes, like H1N1, based on surface proteins of the virus, while influenza B is classified into different lineages rather than the same subtype system.

The flu should not be confused with the so-called "stomach flu." Stomach illnesses that cause vomiting and diarrhea are usually caused by other viruses and are not influenza.

How Virus Causes the Flu?

The influenza virus causes flu or influenza. The virus spreads mainly through respiratory particles released when an infected person coughs, sneezes, talks or breathes.

A person can also become infected after touching contaminated surfaces and then touching their mouth, nose or eyes, although respiratory transmission is an important route.

After entering the body, the virus infects cells of the respiratory tract and begins multiplying. The body's immune response then produces inflammation, which contributes to many of the familiar symptoms of influenza.

Flu Symptoms

Flu symptoms often develop suddenly rather than gradually. Symptoms can vary from person to person, and not everyone develops every symptom.

Common symptoms include:

• Fever, although some people may not have one
• Chills
• Headache
• Muscle or body aches
• Dry or persistent cough
• Sore throat
• Runny or stuffy nose
• Tiredness and weakness
• Reduced appetite
• Watery or painful eyes

Some people, particularly children, may also experience nausea, vomiting or diarrhea.

Flu can sometimes cause wheezing or shortness of breath, especially when the infection affects the lower respiratory tract or aggravates an existing respiratory condition.

How Quickly Do Flu Symptoms Appear?

After exposure to influenza, symptoms usually appear within 1 to 4 days. This period is called the incubation period.

Because people can spread influenza before they realize they are sick, avoiding close contact with others when symptoms begin is important for reducing transmission.

Influenza is highly contagious and can spread between people relatively easily.

People with flu can generally spread the virus beginning about one day before symptoms appear and for several days afterward. They are often most contagious during the first few days of illness.

Young children and people with weakened immune systems may remain infectious for longer.

If you have influenza, staying home when possible, covering coughs and sneezes, improving ventilation and practicing good hand hygiene can help protect others.

How Is Influenza Diagnosed?

Healthcare professionals may diagnose influenza based on symptoms, the time of year, exposure history and physical examination.

When confirmation is needed, a mucus sample from the nose or throat can be tested for influenza viruses. Rapid tests can provide results relatively quickly, while other laboratory tests may take longer but can provide more detailed information.

Testing can be particularly useful when it is important to distinguish influenza from other respiratory infections, including COVID-19.

Flu Treatment

Most otherwise healthy people recover from influenza without specific prescription treatment. Flu treatment generally focuses on helping the body recover and controlling uncomfortable symptoms.

Helpful measures include:

• Getting adequate rest and sleep
• Drinking plenty of fluids
• Using fever and pain medicines when appropriate
• Keeping the room comfortably ventilated
• Using appropriate treatments for congestion or cough when needed

Antiviral medication may also be recommended for some people.

Common influenza antiviral medicines include oseltamivir, zanamivir, peramivir and baloxavir. These medications work against influenza viruses rather than bacteria.

Antivirals generally provide the greatest benefit when started early, often within the first 2 days after symptoms begin. However, people with severe illness or a higher risk of complications may still benefit from antiviral treatment when treatment begins later.

A healthcare professional can determine whether an antiviral is appropriate based on age, health status, symptoms, pregnancy status and other factors. Antibiotics do not treat influenza because antibiotics work against bacteria, not viruses. They may only be needed if a bacterial infection develops as a complication.

How Long Does the Flu Last?

Many people begin to feel better within several days, although complete recovery can take longer.

Fever and intense body aches often improve before respiratory symptoms. A cough, weakness or tiredness may continue after the main symptoms have disappeared. The length and severity of illness can vary depending on the person's age, immune system and overall health.

Who Is More Likely to Develop Flu Complications?

Most people recover without major problems, but influenza can sometimes cause complications.

Possible flu complications include:

• Pneumonia
• Sinus infections
• Ear infections
• Worsening of asthma or other chronic lung disease
• Dehydration
• Severe inflammation affecting other organs in rare cases

Influenza can also make a person more vulnerable to secondary bacterial infections. Pneumonia is one of the most serious complications and may require hospitalization. Severe flu can develop other types of illness like heart attacks, myocarditis and irregular heartbeats.

Higher-risk groups include:

• Adults aged 65 and older
• Children younger than 5, especially very young children
• Pregnant people
• People with asthma or chronic lung disease
• People with heart disease
• People with diabetes
• People with kidney, liver or neurological conditions
• People with weakened immune systems
• People with obesity
• Residents of long-term care facilities

For these groups, contacting a healthcare professional early after developing flu symptoms can be particularly important.

When Should You Seek Medical Care?

Contact a healthcare professional if you have flu symptoms and belong to a high-risk group, develop severe symptoms, or are concerned about your condition.

Prompt medical advice is especially important during pregnancy or when an existing chronic health condition becomes worse.

Seek urgent medical attention for warning signs such as:

• Difficulty breathing or shortness of breath
• Persistent chest pain or pressure
• Confusion or difficulty staying awake
• Severe weakness
• Signs of significant dehydration
• Seizures
• Severe or worsening muscle pain
• Symptoms that improve and then suddenly become worse
• A worsening of an existing medical condition

In children, concerning signs can also include unusually fast breathing, bluish or gray lips or skin, severe dehydration or difficulty waking.

Flu Prevention

The most effective way to reduce the risk of serious influenza is flu vaccination. Because circulating influenza viruses change over time, seasonal vaccination is recommended according to local public health guidance.

Vaccination does not guarantee that someone will never become infected, but it can reduce the risk of influenza and, importantly, severe disease and complications.

Other flu prevention measures include:

• Wash your hands regularly with soap and water.
• Avoid touching your eyes, nose and mouth with unwashed hands.
• Cover your mouth and nose when coughing or sneezing.
• Improve indoor ventilation when possible.
• Avoid close contact with people who are sick.
• Stay home when you are ill.
• Avoid sharing cups, utensils and other personal items.
• Consider wearing a well-fitting mask when respiratory infections are circulating or when close contact with others cannot be avoided.

Influenza vs. Common Cold

Influenza and the common cold can both cause coughing, sore throat and nasal congestion, but they are not the same infection.

Colds are often milder and may develop gradually. Influenza is more likely to begin suddenly and cause prominent fever, chills, headache, body aches and pronounced fatigue.

Symptoms can overlap considerably, so symptoms alone cannot always reliably distinguish influenza from COVID-19 or another respiratory infection. Testing may be necessary when knowing the specific infection would change treatment or precautions.

Final Takeaways

Influenza is a common respiratory infection that can range from a mild illness to a serious disease. Flu symptoms often appear suddenly and may include fever, chills, cough, headache, body aches and significant tiredness.

Most people recover with supportive care, but early medical is advised by the Begin Health Life for people at higher risk of complications. Antiviral medications can be useful in appropriate patients, particularly when started early.

The combination of flu vaccination, good hand hygiene, respiratory precautions and staying home while sick provides an effective approach to reducing influenza transmission and protecting vulnerable people.