Influenza: Symptoms, Causes, Diagnosis and Treatment

Written by Medicover Team and Medically Reviewed by Dr Sateesh Pydi , General Medicine

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1. Causes 2. Find a Doctor 3. Diagnosis 4. Treatment 5. FAQs

Influenza (Flu), commonly known as the seasonal flu, is a highly contagious viral infection that affects the respiratory system. Common influenza symptoms include fever, chills, cough, sore throat, body aches, and fatigue. Early Influenza (Flu) Treatment and receiving the annual flu vaccine can help reduce the severity of illness, prevent complications, and limit the spread of infection.

What Are the Types of Influenza?

Influenza (Flu) viruses are classified into different types based on their genetic characteristics and the populations they affect.

Influenza A

Influenza A is the most common cause of seasonal flu epidemics and has the potential to cause pandemics due to frequent genetic changes.

Most common and widespread type
Can infect humans and animals
Responsible for pandemics

Influenza B and Influenza C

Influenza B causes seasonal outbreaks in humans, while Influenza C usually causes mild respiratory illness and occurs less frequently.

Influenza B affects only humans
Causes seasonal illness
Influenza C generally causes mild disease

What Are the Influenza Symptoms and Warning Signs?

Common Influenza Symptoms Include

Headache
Vomiting and diarrhea are common in some individuals
Cough
Muscle or body aches
Fever or feeling feverish/chills
Fatigue (tiredness)
Runny or stuffy nose
Sore throat

What Are the Common Causes and Risk Factors of Influenza?

Seasonal flu is caused by influenza viruses that infect the nose, throat, and lungs. When sick people cough, sneeze or talk, respiratory particles are released into the air and may infect surrounding individuals. A person can also catch the flu by touching the lips, eyes, or nose with contaminated hands. Some of the causes of influenza are:

Influenza viruses (types A, B, and C) are the primary cause.
Person-to-person transmission through coughing, sneezing, or talking.
Touching contaminated surfaces and then touching the face, eyes, or mouth.
Close contact with infected individuals, especially in crowded settings.
Seasonal changes, particularly in colder months, increase the likelihood of outbreaks.
Weakened immune system, making it easier for the virus to infect.
Underlying health conditions, such as asthma or heart disease, can increase susceptibility.

When To See a Doctor for Influenza?

People with persistent high fever, worsening cough, breathing difficulties, or those at high risk of complications should consult a General Medicine or Pulmonologist promptly.

You should see a doctor if you experience:

Fever lasting more than three days
Persistent cough or worsening sore throat
Symptoms that do not improve or become worse after initial recovery

Seek immediate medical attention if you:

Develop difficulty breathing or persistent chest pain
Experience confusion, seizures, or severe drowsiness
Show signs of dehydration, bluish lips, or symptoms of pneumonia

These symptoms may indicate serious influenza-related complications requiring urgent medical treatment.

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How Is Influenza Diagnosed?

Diagnosis of Influenza disease is based on its symptoms. Physical examination and laboratory tests are conduced when necessary, particularly in hospitalized or high-risk patients.

Early diagnosis allows timely antiviral treatment and helps reduce complications.

Diagnostic Methods

Medical history and physical examination.
Rapid influenza diagnostic test (RIDT).
Reverse transcription polymerase chain reaction (RT-PCR).
Viral culture in selected cases.
Chest X-ray if pneumonia is suspected.
Blood tests when severe infection is suspected.

What Are the Influenza (Flu) Treatment Options?

Influenza (Flu) Treatment depends on symptom severity, underlying health conditions, and the timing of diagnosis. Antiviral medications are most effective when started within 48 hours of symptom onset.

Flu treatment focuses on relieving symptoms, reducing the duration of illness, preventing complications, and supporting recovery through antiviral medications and supportive care when appropriate.

Supportive care remains the mainstay of treatment for uncomplicated influenza.

Medical Treatment

Antiviral medications such as oseltamivir, zanamivir, or baloxavir when indicated.
Paracetamol (acetaminophen) for fever and body aches.
Adequate hydration.
Medications to relieve cough and nasal congestion when appropriate.

Supportive Care

Plenty of rest.
Drinking adequate fluids.
Eating a balanced diet.
Isolating from others until fever-free for at least 24 hours without fever-reducing medication.
Receiving the annual flu vaccine to help prevent influenza and reduce the risk of severe illness.

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What Is the Recovery Process for Influenza?

Most people recover within 7 to 14 days, although fatigue and weakness may persist for several weeks. Individuals with severe illness or underlying medical conditions may require a longer recovery period. Following medical advice and allowing adequate time for rest help prevent complications.

Completing prescribed antiviral treatment, staying hydrated, getting sufficient rest, practicing good hand hygiene, avoiding close contact with others while infectious, and receiving the annual flu vaccine help support recovery and reduce future infections.