What is Posttussive Vomiting?
Posttussive vomiting is vomiting that occurs immediately following a paroxysm (severe bout) of coughing, and it is a highly specific clinical sign for pertussis (whooping cough), though it can occasionally occur with other severe coughing illnesses. 1, 2
Clinical Significance and Diagnostic Value
Posttussive vomiting is one of the three classical characteristics of pertussis, along with paroxysmal cough and inspiratory whooping sound. 2, 3 When evaluating any patient—child or adult—with persistent cough, the presence of posttussive vomiting should immediately raise suspicion for pertussis infection.
Diagnostic Performance
The diagnostic characteristics of posttussive vomiting vary by age:
- In children: Posttussive vomiting has moderate sensitivity (60.0%) and specificity (66.0%) for pertussis. 2, 3
- In adults: Posttussive vomiting has low sensitivity but high specificity (77.7%), meaning when present, it strongly suggests pertussis disease. 3
- Key principle: The absence of posttussive vomiting does not rule out pertussis, but its presence makes pertussis highly likely. 3
Mechanism and Clinical Presentation
Posttussive vomiting occurs because the violent, repetitive coughing paroxysms characteristic of pertussis trigger the vomiting reflex. 1 The coughing episodes are so forceful and prolonged that they lead to:
- Forceful expulsion of gastric contents immediately after the coughing bout ends 4
- Significant nutritional challenges, as patients lose calories and fluids with each episode 4
- Weight loss and feeding difficulties, particularly problematic in infants 4
Clinical Context and Timing
Posttussive vomiting typically appears during the paroxysmal phase of pertussis, which lasts 4-6 weeks and follows the initial 1-2 week catarrhal phase. 3 During this paroxysmal phase:
- Patients experience characteristic paroxysmal cough with posttussive vomiting and inspiratory whoop 3
- Episodes occur more frequently at night, causing substantial sleep disruption 4
- Patients often appear relatively well between coughing episodes despite severe disease 4
Important Clinical Pitfalls
Do not dismiss pertussis in vaccinated adolescents and adults, as the illness can be milder with absent whoop but posttussive vomiting may still be present. 3
In infants under 12 months, posttussive vomiting leads to substantial weight loss and feeding difficulties, requiring hospitalization for nutritional support with frequent small feedings offered immediately after coughing episodes when the infant is less likely to cough. 4
Management Implications
When posttussive vomiting is identified:
- Initiate macrolide antibiotics (preferably azithromycin) immediately when pertussis is suspected, even before laboratory confirmation, to prevent transmission to contacts. 2, 3
- Consider pertussis testing including PCR, culture, or serology. 2
- Provide nutritional support with smaller, more frequent feeds to prevent aspiration and maintain nutrition. 4
- For infants, consider nasogastric or intravenous hydration if vomiting is severe enough to cause dehydration or significant weight loss. 4
Differential Considerations
While posttussive vomiting is highly suggestive of pertussis, it can occasionally occur with other severe coughing illnesses. 1 However, when cough persists >2 weeks accompanied by posttussive vomiting, paroxysms of coughing, or inspiratory whooping sound, pertussis should be the primary diagnostic consideration. 3