What is the most likely diagnosis in a 2‑year‑old with cough, grunting, post‑tussive vomiting, and a single episode of high‑grade fever (39 °C)?

Clinical Diagnosis: Pertussis (Whooping Cough)

This 2-year-old most likely has pertussis (whooping cough), given the combination of cough with post-tussive vomiting, though the presence of fever makes the diagnosis less certain.

Diagnostic Reasoning

Key Clinical Features Present

The child presents with several features suggestive of pertussis 1:

• Cough - The primary symptom
• Post-tussive vomiting - Vomiting triggered by coughing episodes
• Grunting - May represent respiratory distress or could be related to paroxysmal coughing efforts

Pertussis-Specific Assessment in Children

According to the 2019 CHEST guidelines, for children with acute cough (< 4 weeks duration), clinicians should specifically assess for three classical characteristics 1:

1. Paroxysmal cough (recurrent prolonged coughing episodes with inability to breathe during spells)
2. Post-tussive vomiting (vomiting induced by coughing)
3. Inspiratory whooping (continuous inspiratory airway sound with whooping quality)

Post-tussive vomiting in children is moderately sensitive (60%) and specific (66%) for pertussis 1, 2. The CHEST guidelines state that clinicians should consider pertussis as a possible cause when post-tussive vomiting is present in children with acute cough 1.

The Fever Complication

The presence of fever (39°C) creates diagnostic uncertainty. In adults, fever argues against pertussis, but the guidelines are less definitive for children 1. The guideline recommendations focus primarily on adult populations when discussing fever as a negative predictor 1.

Important caveat: The fever was described as a single episode, which may represent:

• An early phase of illness before classic pertussis symptoms fully develop
• A concurrent viral infection
• The initial inflammatory response

Grunting Respirations

The grunting requires careful interpretation. While grunting can indicate serious bacterial infection (including pneumonia) in children, particularly those over 3 months of age 3, it may also represent:

• Respiratory distress from severe coughing paroxysms
• Effort during coughing episodes
• Secondary pneumonia complicating pertussis

Differential Considerations

Other Causes of Post-tussive Vomiting

Asthma should be considered, as post-tussive emesis occurs in 56-71% of children with asthma 4. However, the acute presentation with fever makes this less likely as the primary diagnosis.

Serious bacterial infection (particularly pneumonia) is suggested by the combination of grunting and fever in a 2-year-old 3, and could coexist with or mimic pertussis.

Clinical Approach

Immediate Actions

1. Assess for respiratory distress - The grunting warrants evaluation for pneumonia or other serious bacterial infection, especially given the fever 3

2. Consider laboratory confirmation - Given the moderate sensitivity/specificity of clinical features in children, laboratory testing is important 1:

   • PCR testing (88-100% specific)
   • Culture (100% specific)
   • Testing is most useful early in illness

3. Initiate antibiotic therapy - If pertussis is suspected, treatment should begin immediately to prevent disease spread, even though antibiotics do not alter the clinical course once symptoms are established 1, 5

Key Clinical Pitfalls

• Don't wait for laboratory confirmation to treat if clinical suspicion is high, as early treatment prevents transmission 1, 5
• Don't dismiss pertussis based on fever alone in children, as the evidence for fever ruling out pertussis is stronger in adults than children 1
• Don't overlook concurrent bacterial pneumonia - the grunting and fever combination warrants chest imaging 3
• Remember that pertussis remains endemic despite vaccination programs, with waning immunity over time 5

Risk Considerations

Pertussis carries significant morbidity and mortality risk, particularly in young children 1, 5. At age 2, this child is beyond the highest-risk infant period but still vulnerable to complications.