Bordetella pertussis vs Mycoplasma pneumoniae
How to tell Bordetella pertussis and Mycoplasma pneumoniae apart when a board question makes them look alike.
Pertussis: paroxysmal whooping cough with lymphocytosis; Mycoplasma: gradual walking pneumonia with cold agglutinins.
Side by side
Paroxysmal whooping cough, posttussive emesis, and marked lymphocytosis from pertussis toxin.
Walking atypical pneumonia in school-aged patients or young adults, no cell wall, cold agglutinins, and poor beta-lactam response.
Pertussis toxin ADP-ribosylates Gi, increasing cAMP and causing lymphocytosis; tracheal cytotoxin injures ciliated epithelium.
Mycoplasma lacks a peptidoglycan cell wall and adheres to respiratory epithelium.
Inspiratory whoop, posttussive vomiting, and lymphocytosis point Bordetella.
Interstitial pneumonia, cold agglutinins, and no Gram stain visibility from absent cell wall point Mycoplasma.
The trap
Both cause cough, but pertussis is paroxysmal airway toxin disease while Mycoplasma is atypical pneumonia.
The repair move
For prolonged cough, decide three things: (1) paroxysmal inspiratory whoop with post-tussive emesis plus marked lymphocytosis in an unvaccinated child or adolescent with waning immunity equals Bordetella pertussis (PCR is the diagnostic test of choice; azithromycin shortens infectivity and offer prophylaxis to close contacts especially neonates); (2) gradual mild cough plus low-grade fever plus walking pneumonia picture in a young adult in a dorm or military setting equals Mycoplasma pneumoniae (cold agglutinins, bullous myringitis are classic clues; treat with macrolide, doxycycline, or fluoroquinolone beta-lactams do NOT work because Mycoplasma has no cell wall).
Try a free question
CoreAn infant has paroxysmal coughing spells with inspiratory whoop, posttussive emesis, and marked lymphocytosis. Which organism is most likely?
Show answer and explanation
Answer: A. Bordetella pertussis. B pertussis causes whooping cough with paroxysms, posttussive emesis, and toxin-mediated lymphocytosis.
Why the other choices are tempting
- B. M pneumoniae causes walking atypical pneumonia and lacks a cell wall.
- C. C pneumoniae causes atypical pneumonia/pharyngitis.
- D. H influenzae causes otitis/sinusitis/COPD exacerbation or Hib invasive disease.
- E. RSV causes bronchiolitis, especially in infants.
Flashcards
Tap a card to flip it.
What is the fastest separator for Bordetella pertussis vs Mycoplasma pneumoniae?
Pertussis: paroxysmal whooping cough with lymphocytosis; Mycoplasma: gradual walking pneumonia with cold agglutinins.
What clue should make you choose Bordetella pertussis?
Paroxysmal whooping cough, posttussive emesis, and marked lymphocytosis from pertussis toxin.
Quick answers
What is the fastest way to tell Bordetella pertussis from Mycoplasma pneumoniae?
Pertussis: paroxysmal whooping cough with lymphocytosis; Mycoplasma: gradual walking pneumonia with cold agglutinins.
What is the key clue for Bordetella pertussis?
Paroxysmal whooping cough, posttussive emesis, and marked lymphocytosis from pertussis toxin.
What is the key clue for Mycoplasma pneumoniae?
Walking atypical pneumonia in school-aged patients or young adults, no cell wall, cold agglutinins, and poor beta-lactam response.
What is the common trap with Bordetella pertussis vs Mycoplasma pneumoniae?
Both cause cough, but pertussis is paroxysmal airway toxin disease while Mycoplasma is atypical pneumonia.