What is the likely cause of a dry cough, sore throat, and persistent unpleasant taste in the mouth, and how should it be managed?

Dry Cough, Sore Throat, and Bad Taste in Mouth

The most likely cause is Upper Airway Cough Syndrome (UACS, formerly postnasal drip) from viral upper respiratory infection or rhinitis, and you should start a first-generation antihistamine/decongestant combination immediately while considering recent COVID-19 infection as a potential cause of the taste disturbance. 1

Most Likely Diagnosis

Upper Airway Cough Syndrome (UACS) is the single most common cause of chronic cough in adults, accounting for 18.6-81.8% of cases. 1 The combination of dry cough and sore throat strongly suggests upper airway inflammation with postnasal drainage irritating the pharynx and triggering cough reflexes. 1, 2

The bad taste in mouth adds a critical diagnostic clue:

• Post-viral syndrome (including COVID-19) can cause persistent taste impairment through direct viral effects on taste bud cells and salivary glands that express ACE2 receptors. 3
• GERD mimicking UACS frequently produces upper respiratory symptoms including throat irritation and altered taste, and can coexist with true postnasal drip. 1, 4
• Approximately 20% of UACS cases are "silent" with no obvious postnasal drip symptoms, yet patients still respond to treatment. 1, 2

Immediate First-Line Treatment

Start a first-generation antihistamine/decongestant combination as the most effective evidence-based treatment for UACS. 1, 2 Specific effective combinations include:

• Dexbrompheniramine maleate plus sustained-release pseudoephedrine sulfate 1
• Azatadine maleate plus sustained-release pseudoephedrine sulfate 1
• Chlorpheniramine with sustained-release pseudoephedrine 1

Dosing strategy to minimize sedation: Start with once-daily dosing at bedtime for a few days, then increase to twice-daily therapy. 1 Most patients see improvement within days to 2 weeks. 1

Add Intranasal Corticosteroids

If no improvement after 1-2 weeks with antihistamine/decongestant alone, add fluticasone 100-200 mcg daily for a 1-month trial. 1, 5 Intranasal corticosteroids are the most effective monotherapy for both allergic and non-allergic rhinitis-related UACS. 1 Maximum benefit may not be reached for several days. 5

Symptomatic Cough Relief

While treating the underlying cause:

• Simple home remedies like honey and lemon mixtures should be tried first for benign viral cough. 6
• Dextromethorphan 60 mg provides maximum cough reflex suppression and prolonged relief; standard OTC doses of 15-30 mg are subtherapeutic. 6, 7
• Menthol inhalation (menthol crystals or proprietary capsules) provides acute but short-lived relief. 6

Avoid codeine or pholcodine due to their adverse side effect profile (drowsiness, nausea, constipation, physical dependence) with no greater efficacy than dextromethorphan. 6

Sequential Evaluation if No Response After 2 Weeks

If symptoms persist despite adequate upper airway treatment for 2 weeks, proceed with sequential evaluation for other common causes: 1, 2

1. Asthma/Non-Asthmatic Eosinophilic Bronchitis (NAEB)

• Consider bronchial provocation testing if spirometry is normal 1
• Trial of inhaled corticosteroids 2

2. Gastroesophageal Reflux Disease (GERD)

Initiate empiric therapy with omeprazole 20-40 mg twice daily before meals for at least 8 weeks plus dietary modifications. 1, 8 GERD frequently mimics UACS with upper respiratory symptoms and can cause altered taste. 1, 4 Improvement in cough from GERD treatment may take up to 3 months. 1

Dietary modifications include:

• No more than 45 g of fat in 24 hours 8
• Avoid coffee, tea, soda, chocolate, mints, citrus products (including tomatoes), and alcohol 8
• No smoking 8

3. Post-Viral Cough (if timing suggests recent URI)

If cough duration is 3-8 weeks following a viral upper respiratory infection, this represents subacute post-infectious cough. 7 The presence of clear lungs, normal vital signs, and no fever makes bacterial infection extremely unlikely. 7

Addressing the Bad Taste

The persistent unpleasant taste warrants specific consideration:

• COVID-19 or other viral infection can cause taste impairment through direct effects on oral epithelium, taste buds, and salivary glands. 3 This may persist as "long COVID" even after acute illness resolves. 3
• GERD-related taste disturbance responds to proton pump inhibitor therapy. 4
• Medication side effects: First-generation antihistamines commonly cause dry mouth, which can alter taste. 1

Critical Pitfalls to Avoid

• Do not rely solely on physical examination. The absence of visible postnasal drainage or pharyngeal cobblestoning does not rule out UACS. 1
• Do not overlook "silent" UACS as approximately 20% of patients have no obvious symptoms yet respond to treatment. 1, 2
• Do not use newer-generation antihistamines (cetirizine, fexofenadine, loratadine) for non-allergic UACS, as they are ineffective. 1
• Do not prescribe antibiotics unless there is clear evidence of bacterial sinusitis (purulent discharge >10 days, facial pain, fever, or air-fluid levels on imaging). 1, 7

When to Seek Further Evaluation

Cough persisting beyond 8 weeks meets criteria for chronic cough and requires systematic evaluation. 7, 9 Red flags requiring immediate re-evaluation include:

• Hemoptysis 7
• Fever, night sweats, or weight loss 7
• New or worsening dyspnea 7
• Abnormal lung examination findings 7

Adjunctive Non-Pharmacological Measures

• High-volume saline nasal irrigation (150 mL) mechanically removes secretions and improves mucociliary function, more effective than saline spray. 1
• Adequate hydration to thin mucus 6
• Use of humidifiers to moisten airways 6
• Avoid irritants that trigger cough 6