InfectiousICD-10: J09-J119–41 million illnesses annually in the U.S.
Influenza
Also known as: The Flu, Seasonal Flu
Influenza is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. It can range from mild to severe and can lead to serious complications including pneumonia and death, particularly in high-risk groups. Annual vaccination is the most effective prevention strategy.
Symptoms
Sudden onset of fever and chills
Severe body aches and muscle pain
Headache
Fatigue and weakness (can last up to 2 weeks)
Dry, persistent cough
Sore throat
Runny or stuffy nose
Vomiting and diarrhea (more common in children)
Causes
- Influenza A and B viruses transmitted via respiratory droplets
- Contact with contaminated surfaces
- Airborne transmission in enclosed spaces
- Viral mutations leading to new strains each season
Risk Factors
- Age under 5 or over 65
- Chronic medical conditions
- Pregnancy
- Weakened immune system
- Obesity (BMI ≥40)
- Nursing home residents
Diagnosis
- Rapid influenza diagnostic test
- RT-PCR test (gold standard)
- Clinical diagnosis during known flu season
- Rapid molecular assays
Treatment
- Antiviral medications (oseltamivir, baloxavir) within 48 hours of onset
- Rest and adequate fluid intake
- Acetaminophen or ibuprofen for fever and body aches
- Hospitalization for severe cases
- Avoid aspirin in children (risk of Reye's syndrome)
Prevention
- Get the annual influenza vaccine
- Wash hands frequently
- Avoid close contact with sick individuals
- Stay home when sick
- Cover coughs and sneezes
When to See a Doctor
- You are in a high-risk group and develop flu symptoms
- Symptoms are severe or worsening after initial improvement
- You experience difficulty breathing, chest pain, or confusion
- A child has high fever, inability to drink fluids, or difficulty breathing
Frequently Asked Questions
Related Conditions
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