What are the differential diagnoses for a patient presenting with a dry cough, congestion, and intermittent fevers for one month?

Differential Diagnoses for One Month of Dry Cough, Congestion, and Intermittent Fevers

This patient's symptoms lasting one month place her in the subacute cough category (3-8 weeks), and you must systematically rule out pneumonia first, then consider postinfectious cough, pertussis, evolving asthma, and upper airway cough syndrome as your primary differentials. 1

Immediate Priority: Rule Out Pneumonia

Obtain a chest radiograph to exclude pneumonia, as this fundamentally changes management and cannot be reliably excluded by clinical examination alone. 1, 2

• Check vital signs: heart rate ≥100 bpm, respiratory rate ≥24 breaths/min, or temperature ≥38°C increase pneumonia likelihood 1
• Examine for focal consolidation findings: rales, egophony, or fremitus 1
• The absence of these findings reduces but does not eliminate pneumonia risk—radiography remains essential with fever and one month of symptoms 1, 2

Primary Differential Diagnoses

1. Postinfectious Cough (Most Likely)

This is the leading diagnosis for subacute cough (3-8 weeks) following a presumed viral respiratory infection. 1

• Caused by extensive epithelial disruption and persistent airway inflammation with or without transient bronchial hyperresponsiveness 1
• Typically presents as persistent dry cough after other URI symptoms have resolved 1
• The intermittent fevers suggest ongoing inflammation or possible secondary process 1
• Critical caveat: If symptoms persist beyond 8 weeks total, this diagnosis must be abandoned and chronic cough evaluation initiated 1, 3

2. Pertussis (Bordetella pertussis)

Strongly consider pertussis when cough persists >2 weeks, especially with the constellation of symptoms this patient exhibits. 1, 3

• Look specifically for: paroxysmal coughing episodes, post-tussive vomiting, or inspiratory whooping sound 1, 3
• Pertussis frequency increases to 25-50% during outbreaks 1
• If suspected, antibiotics are indicated to reduce transmission, unlike typical acute bronchitis 4, 5

3. Evolving Asthma (Critical Not to Miss)

Approximately one-third of patients presenting with "acute bronchitis" actually have asthma, and 65% of patients with recurrent bronchitis episodes have underlying mild asthma. 1, 3

• Transient bronchial hyperresponsiveness occurs in 40% of patients after acute respiratory infections, typically resolving within 6 weeks 3
• At one month, persistent symptoms warrant consideration of true asthma rather than transient hyperresponsiveness 1, 3
• Ask about: nocturnal cough worsening, cough triggered by cold air or exercise 1
• Spirometry should be performed if available, though results may be normal in cough-variant asthma 1
• Consider methacholine challenge testing if spirometry is normal but suspicion remains high 1

4. Upper Airway Cough Syndrome (UACS)

The congestion component strongly suggests UACS, which commonly accompanies or follows viral respiratory infections. 1, 3

• Look for: throat clearing, sensation of postnasal drip, nasal discharge, rhinosinusitis symptoms 3
• UACS involves persistent inflammation of nose and paranasal sinuses following viral infection 3
• Often coexists with other causes in a multifactorial pattern 1

5. Atypical Pneumonia (Mycoplasma pneumoniae)

Mycoplasma and other atypical pathogens cause pneumonia with prominent extrapulmonary manifestations and can present with prolonged symptoms. 2

• Chest radiograph is essential to identify infiltrates 2
• May have systemic symptoms beyond typical viral bronchitis 2

Secondary Considerations

Gastroesophageal Reflux Disease (GERD)

• May be triggered by vigorous coughing from initial viral illness 3
• Ask about: heartburn, regurgitation, cough worsening after meals or when supine 3

Persistent Bacterial Bronchitis

• Occurs when initial dry viral cough becomes prolonged wet cough after febrile illness resolves 6
• However, this patient has a DRY cough, making this less likely 6

Critical Diagnostic Steps

1. Chest radiograph (mandatory to rule out pneumonia and structural abnormalities) 1, 2, 7
2. Vital signs assessment (temperature, heart rate, respiratory rate, oxygen saturation) 1, 7
3. Focused physical examination for consolidation findings 1
4. Pertussis-specific history: paroxysmal cough, post-tussive vomiting, whooping, known exposures 1, 3
5. Asthma assessment: nocturnal symptoms, exercise/cold triggers, previous similar episodes 1, 3
6. Medication history: ACE inhibitors (common reversible cause) 7

Critical Pitfalls to Avoid

• Do NOT assume purulent sputum (if it develops) indicates bacterial infection requiring antibiotics—purulence results from inflammatory cells and occurs with viral infections 1
• Do NOT prescribe antibiotics empirically unless pneumonia, pertussis, or bacterial sinusitis is specifically identified—viruses cause >90% of acute bronchitis 4, 5
• Do NOT miss underlying asthma, the most commonly overlooked diagnosis in recurrent "bronchitis" 1, 3
• Do NOT continue calling this "postinfectious cough" if symptoms extend beyond 8 weeks total—at that point, chronic cough evaluation is mandatory 1, 3