I have had a three‑week cough with yellow sputum and now vomiting; what evaluation and treatment are recommended?

Evaluation and Treatment for 3-Week Cough with Yellow Sputum and Vomiting

You need to be evaluated for pertussis (whooping cough), which is the most likely diagnosis given your 3-week cough with post-tussive vomiting, and if confirmed, you should receive a macrolide antibiotic immediately.

Why Pertussis is the Primary Concern

Your presentation strongly suggests pertussis based on two critical features 1, 2:

• Cough lasting ≥2-3 weeks with post-tussive vomiting is highly suggestive of Bordetella pertussis infection
• Post-tussive vomiting in adults has high specificity (79.5%) for pertussis, meaning when present, it strongly points to this diagnosis 2

The 2019 CHEST guidelines specifically state that post-tussive vomiting should rule in a possible diagnosis of pertussis in adults with acute or subacute cough 2.

Immediate Diagnostic Steps

You need the following tests ordered urgently 1:

1. Nasopharyngeal swab or aspirate for culture - this is the gold standard and only certain way to confirm pertussis
2. Paired acute and convalescent sera (if culture unavailable) - looking for 4-fold increase in IgG or IgA antibodies to pertussis toxin

Important caveat: PCR testing is available but not universally validated for routine clinical use 1.

Treatment Algorithm

If Pertussis is Confirmed or Highly Suspected:

Start a macrolide antibiotic immediately 1:

• Treatment within the first few weeks will diminish coughing paroxysms and prevent disease spread
• You must be isolated for 5 days from start of treatment
• Grade A recommendation with substantial benefit 1

Regarding the Yellow Sputum:

Do NOT use antibiotics based on sputum color alone 3, 4:

• Yellow/green sputum does NOT indicate bacterial infection requiring antibiotics in acute cough
• Research shows sputum color has poor specificity (46%) for bacterial infection 4
• Antibiotics provide minimal benefit (reducing cough by only half a day) with significant adverse effects 5

Exception: Antibiotics are only indicated if pertussis is confirmed or if bacterial sinusitis is present 1.

Alternative Diagnosis: Post-Infectious Cough

If pertussis is ruled out, you have post-infectious cough (defined as cough lasting 3-8 weeks after respiratory infection) 1. Treatment options in order:

1. Inhaled ipratropium - first-line therapy (Grade B) 1
2. Inhaled corticosteroids - if ipratropium fails and quality of life is affected 1
3. Prednisone 30-40 mg daily - for severe paroxysms, short finite period only (Grade C) 1
4. Codeine or dextromethorphan - when other measures fail 1

Critical Red Flags to Assess

Before assuming benign post-infectious cough, ensure you don't have 6:

• Fever (suggests ongoing infection, makes pertussis less likely) 2
• Dyspnea, tachypnea, or abnormal lung sounds (suggests pneumonia requiring chest X-ray)
• Paroxysmal cough with inspiratory whooping sound (further supports pertussis) 1, 2

Key Clinical Pitfalls

1. Don't dismiss vomiting as simple gastroenteritis - post-tussive vomiting (vomiting triggered by coughing) is a specific pertussis feature 1, 2
2. Don't prescribe antibiotics for yellow sputum alone - this is not evidence-based and causes harm 3, 4, 5
3. Don't delay pertussis treatment - efficacy decreases significantly after the first few weeks of infection 1
4. If cough persists >8 weeks, this is no longer post-infectious cough and requires full chronic cough workup 1

Bottom Line

Seek medical evaluation immediately for pertussis testing. The combination of 3-week cough with vomiting makes this diagnosis until proven otherwise. If confirmed, macrolide antibiotics are essential to reduce transmission and may still provide some symptom benefit. The yellow sputum alone does not justify antibiotic treatment.