Influenza A vs Influenza B
How to tell Influenza A and Influenza B apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
Pandemic-capable host reassortment is unique to influenza A, while immediate clinical treatment decisions for A and B are otherwise the same.
Side by side
Influenza A has broader host reservoirs and is linked to major antigenic shifts and pandemic potential.
Influenza B is largely human lineage disease causing seasonal outbreaks, especially in children and adolescents.
Segmented RNA reassortment in animal and human hosts enables larger antigenic shifts for influenza A.
Influenza B evolves mostly through drift without the same pandemic shift dynamics as influenza A.
NAAT confirms influenza subtype; severe disease markers include oxygen saturation below 92%, respiratory rate above 24 per min, or progressive bilateral infiltrates requiring hospitalization.
Subtype confirmation also uses NAAT; treatment thresholds are the same, with antiviral benefit greatest when started within 48 hours or later in severe hospitalized illness.
The trap
Students overfocus on subtype and delay antivirals. In Step 2 management, timing and risk profile drive treatment, not whether the swab reports A or B.
The repair move
Next best step: start oseltamivir 75 mg orally twice daily for 5 days immediately, provide hydration and antipyretics, and escalate to hospital care if hypoxemia or respiratory distress worsens. Use the same antiviral framework for influenza A.
Try a free question
CoreA 29-year-old pregnant patient has 24 hours of fever, myalgias, and positive influenza A PCR. She is stable for outpatient treatment. What is the next best step in management?
Show answer and explanation
Answer: A. Start oseltamivir now. Pregnancy is high risk, so antiviral therapy should start promptly when influenza is suspected or confirmed.
Why the other choices are tempting
- B. Waiting forfeits early antiviral benefit.
- C. Antibiotics do not treat primary influenza infection.
- D. Aspirin-only care is inadequate and potentially unsafe in viral illness contexts.
- E. Young age does not negate pregnancy-associated risk.
Flashcards
Tap a card to flip it.
Which influenza type is associated with pandemic-scale antigenic shift?
Influenza A.
How should antiviral treatment differ between influenza A and B in high-risk symptomatic adults?
It generally does not differ; treat based on timing and severity with neuraminidase inhibitors.
Quick answers
What is the fastest way to tell Influenza A from Influenza B?
Pandemic-capable host reassortment is unique to influenza A, while immediate clinical treatment decisions for A and B are otherwise the same.
What is the key clue for Influenza A?
Influenza A has broader host reservoirs and is linked to major antigenic shifts and pandemic potential.
What is the key clue for Influenza B?
Influenza B is largely human lineage disease causing seasonal outbreaks, especially in children and adolescents.
What is the common trap with Influenza A vs Influenza B?
Students overfocus on subtype and delay antivirals. In Step 2 management, timing and risk profile drive treatment, not whether the swab reports A or B.