Common Colds for USMLE Step 2
Common colds for the USMLE Step 2 Exam
Pathophysiology
- Viral Infection:
- The common cold is caused by viral infections of the upper respiratory tract. Rhinoviruses are the most frequent pathogens (accounting for 50% of cases), followed by coronaviruses, adenoviruses, and respiratory syncytial virus (RSV).
- Rhinoviruses enter nasal epithelial cells by binding to intercellular adhesion molecule-1 (ICAM-1), triggering a local inflammatory response.
- Immune Response:
- Infected epithelial cells release cytokines (e.g., IL-1, IL-6, TNF-α), promoting vasodilation, increased vascular permeability, and mucus production. These inflammatory responses lead to the characteristic symptoms of nasal congestion, rhinorrhea, and sore throat.
- Transmission:
- Spread occurs via:
- Direct contact: With contaminated surfaces or objects.
- Aerosolized droplets: When an infected person sneezes or coughs.
Clinical Features
- Nasal Congestion and Rhinorrhea:
- These are the hallmark symptoms of the common cold. Rhinorrhea typically begins as clear, watery discharge but may become thicker and more purulent as the illness progresses.
- Sore Throat:
- Pharyngitis is common early in the illness due to viral inflammation of the mucosa.
- Cough:
- Cough may start early or develop later, often due to postnasal drip.
- Sneezing and Malaise:
- Sneezing is frequent early in the illness, and mild fatigue or malaise often accompanies other symptoms.
- Fever:
- Low-grade fever may occur in children but is uncommon in adults with a typical cold.
- Duration:
- Symptoms usually last 7-10 days, though cough may persist for up to 2 weeks.
Diagnosis
- Clinical Diagnosis:
- Diagnosis is based on characteristic symptoms, including gradual-onset nasal congestion, sore throat, and cough without high fever or severe systemic illness.
- Differential Diagnosis:
- Influenza: More severe systemic symptoms (e.g., high fever, body aches) and abrupt onset.
- Allergic Rhinitis: Persistent sneezing, itchy eyes, and clear nasal discharge without fever.
- Sinusitis: Symptoms lasting more than 10 days, facial pain, and purulent nasal discharge suggest bacterial sinusitis.
Management
Symptomatic Treatment
- Nasal Decongestants:
- Intranasal decongestants (e.g., oxymetazoline) reduce nasal congestion via vasoconstriction but should be limited to 3-5 days to avoid rebound congestion (rhinitis medicamentosa).
- Oral decongestants (e.g., pseudoephedrine) are effective but may cause systemic side effects like hypertension and insomnia.
- Antihistamines:
- First-generation antihistamines (e.g., diphenhydramine) may alleviate sneezing and rhinorrhea by reducing mucus production but can cause sedation.
- Analgesics:
- Acetaminophen or ibuprofen can be used to reduce headache, fever, and body aches. Aspirin is not recommended in children due to the risk of Reye syndrome.
- Cough Suppressants:
- Dextromethorphan may provide temporary relief for bothersome cough, though its efficacy in colds is limited.
Supportive Care
- Hydration:
- Drinking fluids helps to thin mucus, making it easier to clear nasal secretions.
- Rest:
- Rest supports the immune response and can help alleviate fatigue.
- Humidification and Saline Sprays:
- Humidifiers and saline nasal sprays soothe irritated nasal passages and ease congestion.
Prevention
- Hand Hygiene:
- Washing hands with soap or using alcohol-based hand sanitizers is the most effective preventive measure against the common cold.
- Avoiding Close Contact:
- Staying away from infected individuals and practicing good respiratory hygiene (e.g., covering coughs and sneezes) reduces transmission.
Complications
- Secondary Bacterial Infections:
- Secondary bacterial sinusitis or otitis media may develop in some cases, characterized by worsening symptoms after initial improvement.
- Asthma Exacerbations:
- Viral infections can trigger asthma exacerbations in susceptible individuals.
- Exacerbation of Chronic Lung Disease:
- In patients with chronic obstructive pulmonary disease (COPD), viral infections may lead to exacerbations.
Key Points
- The common cold is a viral upper respiratory tract infection caused primarily by rhinoviruses. Other pathogens include coronaviruses, adenoviruses, and respiratory syncytial virus (RSV).
- Symptoms include nasal congestion, rhinorrhea, sore throat, cough, sneezing, and malaise, with fever being rare in adults.
- Diagnosis is clinical, based on symptom pattern, with management focused on supportive care (e.g., nasal decongestants, antihistamines, analgesics, and hydration).
- Antibiotics are not indicated for the common cold, and prevention relies on proper hand hygiene and respiratory hygiene.
- Complications, though rare, include secondary bacterial infections and exacerbations of asthma or COPD.