Influenza vs Parainfluenza
How to tell Influenza and Parainfluenza apart when a board question makes them look alike.
Influenza is abrupt systemic myalgia fever-cough illness; parainfluenza is croup with barking cough and stridor.
Side by side
Influenza causes abrupt fever, chills, myalgias, headache, malaise, dry cough, sore throat, and risk of viral pneumonia or secondary bacterial pneumonia.
Parainfluenza classically causes croup with barking cough, hoarseness, inspiratory stridor, and steeple sign, especially in young children.
Influenza A and B are segmented negative-sense RNA orthomyxoviruses with antigenic drift; influenza A can undergo shift.
Parainfluenza viruses infect upper/lower airways and commonly inflame larynx/trachea, producing croup.
Sudden systemic myalgias, fever during flu season, PCR/rapid testing, and post-influenza S. aureus or S. pneumoniae pneumonia support influenza.
Barking cough, stridor, hoarseness, subglottic narrowing/steeple sign, and response to dexamethasone/epinephrine support croup from parainfluenza.
The trap
Both are respiratory viruses, but upper-airway obstruction signs point to parainfluenza croup rather than influenza.
The repair move
For winter respiratory illness, separate systemic myalgias from croup airway signs.
Try a free question
CoreAn adult develops abrupt fever, chills, severe myalgias, headache, malaise, sore throat, and dry cough during winter. Which virus is most likely?
Show answer and explanation
Answer: A. Influenza virus. Abrupt systemic fever, myalgias, malaise, and dry cough during flu season support influenza.
Why the other choices are tempting
- B. Parainfluenza classically causes croup.
- C. RSV classically causes bronchiolitis in infants.
- D. Adenovirus can cause pharyngoconjunctival fever or pneumonia.
- E. EBV causes mononucleosis.
Flashcards
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What symptom cluster supports influenza?
Abrupt fever, chills, myalgias, malaise, headache, and dry cough support influenza.
What antigenic process is unique to influenza A pandemics?
Antigenic shift can produce influenza A pandemics.
Quick answers
What is the fastest way to tell Influenza from Parainfluenza?
Influenza is abrupt systemic myalgia fever-cough illness; parainfluenza is croup with barking cough and stridor.
What is the key clue for Influenza?
Influenza causes abrupt fever, chills, myalgias, headache, malaise, dry cough, sore throat, and risk of viral pneumonia or secondary bacterial pneumonia.
What is the key clue for Parainfluenza?
Parainfluenza classically causes croup with barking cough, hoarseness, inspiratory stridor, and steeple sign, especially in young children.
What is the common trap with Influenza vs Parainfluenza?
Both are respiratory viruses, but upper-airway obstruction signs point to parainfluenza croup rather than influenza.