Common Colds for USMLE Step 1
Common colds for the USMLE Step 1 Exam
Pathophysiology
- Viral Infection:
- The common cold is primarily caused by viral infections of the upper respiratory tract. Rhinoviruses are the most common pathogen (accounting for 50% of cases), followed by coronaviruses, adenoviruses, respiratory syncytial virus (RSV), and enteroviruses.
- The virus enters through the nasal or conjunctival mucosa, binding to epithelial cell receptors (e.g., intercellular adhesion molecule-1 [ICAM-1] for rhinoviruses), initiating infection and inflammation.
- Immune Response:
- Infected epithelial cells release pro-inflammatory cytokines (e.g., IL-1, IL-6, TNF-α), causing vasodilation, increased vascular permeability, and mucus production. This immune response leads to the characteristic symptoms of nasal congestion, rhinorrhea, and sore throat.
- Transmission:
- Transmission occurs via direct contact with contaminated surfaces or aerosolized droplets when an infected person coughs or sneezes.
Clinical Features
- Nasal Congestion and Rhinorrhea:
- These are the most prominent symptoms, beginning as clear, watery discharge, which may become thicker and more purulent as the infection progresses.
- Sore Throat:
- Pharyngitis or a mild sore throat is often an early symptom, secondary to inflammation of the pharyngeal mucosa.
- Cough:
- A nonproductive cough is common, especially as postnasal drip increases later in the illness.
- Sneezing:
- Often an initial symptom, sneezing results from irritation of the nasal mucosa.
- Malaise and Fatigue:
- Generalized mild fatigue and malaise are common but less severe than in other viral infections like influenza.
- Fever:
- Fever is uncommon in adults but may occur in children with more pronounced systemic symptoms.
- Duration:
- Symptoms typically last for 7-10 days, though a residual cough may persist for up to two weeks.
Diagnosis
- Clinical Diagnosis:
- Diagnosis is made clinically based on history and physical examination. The presence of gradual-onset symptoms, nasal congestion, rhinorrhea, and absence of severe systemic signs (e.g., high fever, myalgia) help differentiate the common cold from other respiratory infections.
- Differential Diagnosis:
- Influenza: More severe systemic symptoms (e.g., abrupt fever, myalgia).
- Acute Sinusitis: Prolonged congestion (>10 days), facial pain, and purulent nasal discharge suggest bacterial infection.
- Allergic Rhinitis: Clear nasal discharge, sneezing, and itchy eyes without fever or systemic illness.
Management
Symptomatic Treatment
- Nasal Decongestants:
- Topical decongestants (e.g., oxymetazoline) reduce nasal congestion by 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 side effects such as insomnia or tachycardia.
- Antihistamines:
- First-generation antihistamines (e.g., diphenhydramine) may reduce rhinorrhea and sneezing through anticholinergic effects but cause sedation.
- Analgesics:
- Acetaminophen and ibuprofen are effective for treating headache, fever, and body aches. Aspirin should be avoided in children due to the risk of Reye syndrome.
- Cough Suppressants:
- Dextromethorphan may be used to suppress a bothersome cough, though its efficacy is limited.
Supportive Care
- Hydration:
- Adequate hydration helps to thin mucus secretions, promoting easier clearance.
- Rest:
- Rest is essential for recovery and supporting the immune system's response.
- Humidification:
- Using a humidifier or saline nasal sprays helps soothe the nasal passages and reduce congestion.
Prevention
- Hand Hygiene:
- Frequent handwashing with soap or using alcohol-based hand sanitizers reduces transmission by minimizing contact with contaminated surfaces.
- Respiratory Hygiene:
- Covering coughs and sneezes and avoiding close contact with infected individuals helps reduce the spread of viral particles.
- Vaccines:
- No vaccine exists for the common cold, but vaccines for influenza and other respiratory viruses (e.g., COVID-19) can reduce the burden of respiratory infections overall.
Key Points
- The common cold is a viral upper respiratory infection primarily caused by rhinoviruses. Other causative agents include coronaviruses, RSV, and adenoviruses.
- Symptoms include nasal congestion, rhinorrhea, sore throat, cough, sneezing, and mild malaise. Fever is rare in adults but may occur in children.
- Diagnosis is clinical, based on gradual symptom onset and mild systemic involvement. Treatment is supportive, focusing on symptom relief through nasal decongestants, antihistamines, and hydration.
- Prevention focuses on hand hygiene and respiratory hygiene, as there is no vaccine available for the common cold.