Common Colds for USMLE Step 3
Common colds for the USMLE Step 3 Exam
Pathophysiology
- Viral Infection:
- The common cold is primarily caused by viral pathogens. Rhinoviruses are the most common cause (50% of cases), followed by coronaviruses, adenoviruses, and respiratory syncytial virus (RSV).
- Viruses infect the upper respiratory tract by binding to host epithelial receptors (e.g., intercellular adhesion molecule-1 [ICAM-1] for rhinoviruses), initiating local inflammation and triggering an immune response.
- Immune Response:
- Infected cells release pro-inflammatory cytokines, such as IL-1, IL-6, and TNF-α, leading to vasodilation, increased vascular permeability, and mucus production. This immune response manifests as rhinorrhea, nasal congestion, and pharyngitis.
- Transmission:
- The cold is highly contagious and is transmitted primarily by:
- Direct contact with contaminated surfaces or hands.
- Respiratory droplets from coughing or sneezing.
Clinical Features
- Nasal Congestion and Rhinorrhea:
- Nasal congestion and watery rhinorrhea are common early symptoms, with rhinorrhea potentially becoming thicker as the infection progresses.
- Sore Throat:
- Mild pharyngitis or throat discomfort is common, particularly early in the illness.
- Cough:
- Cough may develop later in the illness, often due to postnasal drip or airway irritation.
- Sneezing:
- Frequent sneezing is an early symptom caused by irritation of the nasal mucosa.
- Malaise and Fatigue:
- Generalized, mild fatigue is often present but typically less severe than in influenza.
- Fever:
- Fever is uncommon in adults but may occur in children, especially in the early stages of illness.
- Duration:
- Symptoms usually last 7-10 days, though a cough may persist for up to two weeks.
Diagnosis
- Clinical Diagnosis:
- Diagnosis is clinical, based on characteristic symptoms such as nasal congestion, rhinorrhea, and mild sore throat. The absence of high fever and severe systemic symptoms helps differentiate the common cold from other illnesses.
- Differential Diagnosis:
- Influenza: More abrupt onset, higher fever, and severe body aches.
- Allergic Rhinitis: Persistent sneezing, clear nasal discharge, and itchy eyes without systemic symptoms or fever.
- Acute Bacterial Sinusitis: Prolonged nasal congestion (>10 days), facial pain, and purulent discharge.
Management
Symptomatic Treatment
- Nasal Decongestants:
- Topical decongestants (e.g., oxymetazoline) reduce nasal congestion via vasoconstriction but should not be used for more than 3-5 days to avoid rebound congestion (rhinitis medicamentosa).
- Oral decongestants (e.g., pseudoephedrine) are effective but can cause side effects like hypertension and insomnia.
- Antihistamines:
- First-generation antihistamines (e.g., diphenhydramine) may reduce sneezing and rhinorrhea but are associated with sedation. Second-generation antihistamines are less sedating but have limited effectiveness in colds.
- Analgesics and Antipyretics:
- Acetaminophen and ibuprofen can alleviate headache, fever, and body aches. Aspirin should be avoided in children due to the risk of Reye syndrome.
- Cough Suppressants and Expectorants:
- Dextromethorphan may help suppress a dry cough. Guaifenesin may facilitate mucus clearance in productive coughs but has limited effectiveness in common colds.
Supportive Care
- Hydration:
- Drinking plenty of fluids helps to thin mucus and ease congestion.
- Humidification:
- Using a humidifier or vaporizer can relieve nasal congestion and soothe the throat by keeping the airways moist.
- Rest:
- Adequate rest supports the immune response and helps the body recover.
- Saline Nasal Sprays:
- These sprays help clear nasal passages and reduce congestion by thinning mucus.
Prevention
- Hand Hygiene:
- Frequent handwashing with soap or using alcohol-based hand sanitizers reduces the risk of virus transmission.
- Respiratory Hygiene:
- Covering coughs and sneezes and avoiding close contact with infected individuals reduce the spread of infection.
Complications
- Secondary Bacterial Infections:
- Although uncommon, secondary infections such as acute bacterial sinusitis or otitis media can occur, usually after a prolonged cold with worsening symptoms.
- Asthma Exacerbations:
- Viral upper respiratory infections can trigger asthma exacerbations, leading to increased coughing, wheezing, and shortness of breath.
- Exacerbations of Chronic Lung Disease:
- Patients with chronic obstructive pulmonary disease (COPD) are at increased risk of exacerbations during viral infections.
Key Points
- The common cold is caused by viral pathogens, primarily rhinoviruses, and is characterized by nasal congestion, rhinorrhea, sore throat, and cough.
- Symptoms typically last 7-10 days, with fever being rare in adults but more common in children.
- Diagnosis is clinical, and treatment is supportive, focusing on symptom relief with decongestants, antihistamines, analgesics, and hydration.
- Antibiotics are not indicated for the common cold. Prevention relies on good hand hygiene and respiratory hygiene.
- Complications include secondary bacterial infections and exacerbations of asthma or chronic lung disease.