Influenza for PA
Influenza for the Physician Assistant Licensing Exam
Etiology
- Influenza Virus:
- Influenza is caused by influenza A and B viruses.
- Influenza A is responsible for most epidemics and pandemics and can undergo antigenic drift (small mutations) and antigenic shift (major reassortment).
- Influenza B causes seasonal outbreaks but does not undergo antigenic shift.
Transmission
- Respiratory Droplets:
- Spread primarily through droplets from coughing, sneezing, or talking.
- Can also spread via contaminated surfaces.
- Seasonality:
- Common during the winter months in temperate regions.
Pathophysiology
- Viral Replication:
- The virus infects respiratory epithelial cells, damaging them and impairing mucociliary clearance.
- This leads to systemic symptoms from cytokine release (e.g., interferons, IL-6, TNF-α).
Clinical Features
- Systemic Symptoms:
- Sudden onset of fever, severe myalgias, headache, and fatigue.
- Respiratory Symptoms:
- Dry cough, sore throat, and rhinorrhea.
- Gastrointestinal Symptoms:
- More common in children, presenting as nausea, vomiting, or diarrhea.
Complications
- Primary Viral Pneumonia:
- Presents with dyspnea, hypoxia, and bilateral infiltrates on chest X-ray.
- Secondary Bacterial Pneumonia:
- Recurrence of fever and productive cough. Common pathogens include S. pneumoniae and S. aureus.
- Exacerbation of Chronic Conditions:
- Includes asthma, COPD, and heart failure.
Diagnosis
- Clinical Diagnosis:
- Based on sudden onset of fever, myalgias, and respiratory symptoms during flu season.
- Laboratory Testing:
- RT-PCR is the gold standard for confirming the diagnosis.
Management
- Antiviral Therapy:
- Oseltamivir or zanamivir are most effective if started within 48 hours of symptom onset. They reduce illness duration and severity.
- Supportive Care:
- Symptomatic treatment includes antipyretics, rest, hydration, and cough suppressants.
Prevention
- Annual Vaccination:
- Recommended for all individuals ≥6 months, especially high-risk populations such as the elderly, pregnant women, and those with chronic conditions.
Key Points
- Influenza is caused by influenza A and B viruses, transmitted via respiratory droplets, and characterized by sudden onset of fever, myalgias, and respiratory symptoms.
- Antiviral treatment with neuraminidase inhibitors (e.g., oseltamivir) is most effective when started within 48 hours.
- Annual influenza vaccination is the best prevention method for all individuals ≥6 months.