Influenza (Flu): Types, Causes, Signs and Symptoms, Diagnosis, Prevention, and Treatment
Introduction
• Influenza, commonly known as the flu, is a highly contagious viral respiratory illness that affects millions of people worldwide every year. It spreads easily through droplets released when an infected person coughs, sneezes, or talks. Influenza infections can range from mild to severe, and in some cases, may even lead to hospitalization or death, especially in vulnerable populations such as children, elderly adults, pregnant women, and those with weakened immune systems.
• Understanding influenza is crucial because it is one of the most common seasonal epidemics. Despite being preventable through vaccines and manageable with timely treatment, influenza continues to pose a significant global health burden.
In this detailed article, we will explore:
• What influenza is
• The different types of influenza viruses
• Causes and risk factors
• Common signs and symptoms
Methods of diagnosis
Prevention strategies including vaccines and hygiene practices
Available treatment options
What is Influenza?
• Influenza is an acute viral infection caused by influenza viruses that belong to the family Orthomyxoviridae. It primarily affects the nose, throat, and lungs, leading to respiratory symptoms. Unlike the common cold, influenza usually comes on suddenly, with more severe and long-lasting effects.
• The flu is known for its seasonal outbreaks, particularly during colder months. These outbreaks can lead to widespread absenteeism from work and school, overburdening healthcare systems.
Types of Influenza
There are four major types of influenza viruses: A, B, C, and D. Each type has unique characteristics and impacts.
1. Influenza A
• Most common and dangerous type.
• Responsible for major flu pandemics (e.g., the 1918 Spanish Flu, 2009 H1N1 Swine Flu).
• Found in humans, birds, and other animals.
Subtypes are based on two surface proteins:
• Hemagglutinin (H)
• Neuraminidase (N)
Examples: H1N1, H3N2.
2. Influenza B
• Found only in humans.
• Usually less severe than Type A.
• Can cause seasonal epidemics.
No subtypes like Influenza A, but categorized into two lineages:
• B/Yamagata
• B/Victoria
3. Influenza C
• Rare and milder.
• Causes mild respiratory illness.
• Not responsible for epidemics.
4. Influenza D
• Primarily affects cattle.
• No known human infections so far.
Causes of Influenza
Influenza is caused by infection with influenza viruses. The virus spreads mainly through:
1. Airborne transmission – Droplets from coughing, sneezing, or talking.
2. Direct contact – Shaking hands or touching an infected person.
3. Surface contamination – Touching contaminated surfaces (doorknobs, phones) and then touching mouth, nose, or eyes.
Risk Factors
Certain groups are at higher risk of developing severe flu complications:
• Children under 5 years
• Adults over 65 years
Pregnant women
• People with chronic conditions (asthma, diabetes, heart disease)
• Immunocompromised individuals
Signs and Symptoms of Influenza
The symptoms of influenza often appear suddenly within 1–4 days of exposure.
Common Symptoms:
• High fever (usually over 100.4°F or 38°C)
• Chills and sweats
• Headache
• Muscle aches (myalgia)
• Fatigue and weakness
• Cough (dry, persistent)
• Sore throat
• Runny or stuffy nose
Less Common Symptoms:
• Vomiting
• Diarrhea (more common in children than adults)
• Severe Symptoms (Complications):
• Difficulty breathing
• Chest pain
• Confusion
• Persistent dizziness
• Seizures
Diagnosis of Influenza
Diagnosing influenza is essential to differentiate it from other respiratory infections such as the common cold, COVID-19, or pneumonia.
Diagnostic Methods:
1. Clinical Evaluation
• Based on symptoms and patient history.
• Sudden onset of fever, cough, and body aches raises suspicion.
2. Rapid Influenza Diagnostic Tests (RIDTs)
• Detect viral antigens within 10–15 minutes.
• Less sensitive; false negatives possible.
3. Rapid Molecular Assays
• Detect viral genetic material.
• More accurate than RIDTs.
4. Reverse Transcription Polymerase Chain Reaction (RT-PCR)
• Gold standard test.
• Detects specific influenza virus type and subtype.
5. Viral Culture
• Rarely used in routine practice.
• Helps in epidemiological studies and vaccine development.
Prevention of Influenza
Preventing influenza is more effective than treating it. The most important preventive measure is vaccination.
1. Influenza Vaccination
Annual flu vaccines recommended for everyone above 6 months of age.
Available forms:
• Inactivated influenza vaccine (IIV) – injection.
• Live attenuated influenza vaccine (LAIV) – nasal spray (for certain age groups).
• Updated yearly to match circulating strains.
2. Personal Hygiene Measures
• Wash hands frequently with soap and water.
• Use alcohol-based hand sanitizers.
• Avoid touching face (mouth, nose, eyes) with unwashed hands.
3. Respiratory Hygiene
• Cover mouth and nose when coughing/sneezing.
• Dispose of tissues properly.
• Wear masks in crowded places during outbreaks.
4. Lifestyle Measures
• Maintain strong immunity through balanced diet, adequate sleep, and regular exercise.
• Stay hydrated.
5. Avoiding Exposure
• Stay away from crowded places during flu season.
• Isolate infected individuals to reduce spread.
Treatment of Influenza
Most cases of influenza are mild and resolve within 1–2 weeks without medical treatment. However, some cases require medical intervention.
1. Supportive Care
• Rest
• Adequate hydration
• Pain relievers and fever reducers (acetaminophen, ibuprofen)
• Warm fluids and throat lozenges for sore throat
2. Antiviral Medications
Antiviral drugs are most effective when taken within 48 hours of symptom onset.
• Oseltamivir (Tamiflu) – oral
• Zanamivir (Relenza) – inhaled
• Peramivir (Rapivab) – intravenous
• Baloxavir marboxil (Xofluza) – single-dose oral treatment
These drugs help:
• Shorten duration of illness
• Reduce severity of symptoms
• Prevent complications
3. Hospitalization
Severe cases may require hospitalization for:
• Oxygen therapy
• Intravenous fluids
• Mechanical ventilation in critical cases
Complications of Influenza
If left untreated or in high-risk groups, influenza can lead to:
• Pneumonia (viral or bacterial)
• Bronchitis
• Asthma flare-ups
• Heart problems (myocarditis, pericarditis)
• Multi-organ failure in rare cases
Global Burden of Influenza
According to the World Health Organization (WHO):
• Every year, 1 billion people are infected with influenza.
• Around 3–5 million develop severe illness.
• Between 290,000 and 650,000 deaths occur annually from influenza-related respiratory diseases.
• This highlights the need for global vaccination campaigns and public awareness.
Difference Between Influenza and Common Cold
Feature Influenza (Flu) Common Cold
• Onset Sudden Gradual
Fever High, common Rare or mild
• Body aches Severe Mild
• Fatigue Severe, lasts weeks Mild, short-lived
• Complications Serious (pneumonia etc.) Rare
Conclusion
• Influenza remains a major public health challenge due to its contagious nature and potential for complications. Awareness, vaccination, and early treatment are the keys to reducing its impact.
• By practicing good hygiene, getting vaccinated annually, and seeking timely medical care, individuals can protect themselves and others from the flu.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group)