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🩺 Disease of the Day — Day 1

The Common Cold (Acute Viral Rhinitis / Rhinopharyngitis)

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📌 At a Glance

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1. ETIOLOGY - What Causes It?

• Rhinovirus - the superstar. Over 100 serotypes (types). Part of the Picornaviridae family. This is why you can catch a cold over and over - every infection only protects you against that one specific serotype.
• Seasonal Coronaviruses (not SARS-CoV-2) - responsible for ~15% of colds
• Parainfluenza viruses
• Respiratory Syncytial Virus (RSV)
• Adenovirus, Enterovirus, Metapneumovirus

Any single serotype of rhinovirus accounts for <1% of all colds in a year - that tells you just how diverse the viral landscape is. - Fishman's Pulmonary Diseases and Disorders

Why does rhinovirus love the nose?

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2. TRANSMISSION - How Does It Spread?

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3. PATHOGENESIS - What Happens Inside the Body?

Virus enters → Binds ICAM-1 receptor on nasal epithelium
     ↓
Minimal actual cell damage (unlike flu)
     ↓
Immune system activated → Bradykinin & Kinin release
     ↓
Bradykinin causes: vasodilation + hypersecretion + sore throat
     ↓
Symptoms are IMMUNE-MEDIATED, not virus-mediated

• The real culprit is bradykinin (a kinin peptide) - levels are elevated in nasal secretions during rhinovirus infection
• Bradykinin causes: nasal congestion, runny nose, vasodilation, and sore throat
• The virus causes minimal direct mucosal cell damage - which explains why you feel bad but recover quickly

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4. CLINICAL FEATURES - What Does the Patient Feel?

Timeline of symptoms:

Day 0-1: Sore throat (often the first symptom), malaise
Day 1-2: Nasal congestion, sneezing, rhinorrhea begin
Day 2-4: Peak symptoms - runny nose, stuffiness, cough begins
Day 5-7: Gradual improvement in most adults
Day 7-14: Residual cough may persist

Typical symptom checklist:

• ✅ Nasal congestion / stuffiness
• ✅ Rhinorrhea (watery → thick → colored discharge as days pass)
• ✅ Sneezing
• ✅ Sore throat
• ✅ Mild cough (variable)
• ✅ Malaise / mild fatigue
• ✅ Hoarse voice
• ❌ High fever (absent in adults - this is a key distinguisher from flu!)
• ❌ Severe myalgia / body aches (that's flu)

"Patients often report chills, but fever is not a typical feature of uncomplicated colds. Cough and hoarseness are variably present." - Fishman's Pulmonary Diseases and Disorders

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5. COMPLICATIONS - When Does It Get Worse?

Rhinoviruses are the #1 cause of asthma exacerbations in both children and adults. - Fishman's Pulmonary Diseases and Disorders

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6. DIAGNOSIS - How Do You Diagnose It?

When to think otherwise:

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7. TREATMENT - How Do You Manage It?

The Golden Rule: Supportive care only

"The goal of treatment for the common cold is supportive care." - Tintinalli's Emergency Medicine

What works (symptom relief):

What does NOT work (or is harmful):

• ❌ Antibiotics - viral disease; antibiotics cause harm, no benefit
• ❌ Antihistamines alone - not effective for viral rhinitis
• ❌ Vitamin C - widely used, evidence is weak and inconclusive
• ❌ Zinc - mixed evidence; some benefit if taken within 24 hours of onset
• ❌ Echinacea - not proven effective
• ❌ Cough/cold medicines in children ≤6 years - avoid entirely due to risk of harm

Special note on children:

Never give cough/cold combination medicines to children under 6 years. Use saline nasal drops, bulb suctioning, cool-mist humidifiers, and honey (if >1 year). - Harrison's Principles of Internal Medicine 22E

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8. PREVENTION - How Do You Stop It Spreading?

• Hand hygiene - undeniable benefit, reduces transmission
• Avoid touching eyes/nose with unwashed hands
• Masks and distancing - now well-established as effective (lesson from COVID era)
• No vaccine available - 100+ serotypes of rhinovirus make vaccine development extremely difficult. Researchers have explored monoclonal antibodies targeting ICAM-1 (the receptor), but nothing is in clinical use yet.

"The multiplicity of serotypes and their tendency to be type-specific in the production of antibodies demand the development of a multivalent vaccine - which would be extremely difficult to accomplish." - Sherris & Ryan's Medical Microbiology

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9. MNEMONIC SUMMARY

• C - Caused by Rhinovirus (>50%), spread via airborne >> fomites
• O - Only supportive treatment; antibiotics = useless
• L - Lasts 7-10 days; ICAM-1 receptor; Bradykinin = main symptom mediator
• D - Differentials: Flu (fever+myalgia), Strep (exudate+nodes), Mono (young adult+lymphadenopathy)

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10. HIGH-YIELD EXAM FACTS

1. Rhinovirus grows best at 33°C (nasopharyngeal temp) - explains upper airway tropism
2. Virus binds ICAM-1 receptor - this is the target for experimental monoclonal antibodies
3. Symptoms are immune-mediated via bradykinin, not from direct viral cell killing
4. No fever in adults - distinguishes from influenza
5. >100 serotypes = no vaccine; re-infection is lifelong
6. Antibiotics are never indicated unless clear secondary bacterial infection (sinusitis, otitis media)
7. Anosmia post-viral is a recognized complication (particularly relevant after any severe cold - predates COVID awareness)
8. Rhinovirus is the #1 trigger of asthma exacerbations

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📅 Coming Up Next (Day 2)

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🔍 The "It Looks Like a Cold" Differential Diagnosis - Complete Breakdown

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The 7 Diseases That Masquerade as Each Other

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DISEASE 1: Common Cold (Your Baseline)

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DISEASE 2: Influenza (Flu)

• Severe myalgia (muscle aches) - this is the hallmark
• Severe headache
• Fatigue so bad they can't get out of bed
• Dry cough (not runny)
• Runny nose is MINIMAL compared to a cold

• Oseltamivir (Tamiflu) 75mg twice daily x 5 days - only works if given within 48 hours of symptom onset
• Zanamivir (inhaled) - alternative
• Paracetamol/ibuprofen for fever and myalgia
• Rest and hydration
• Annual flu vaccine - most important prevention

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DISEASE 3: Strep Throat (Group A Streptococcal Pharyngitis)

• Severe sore throat - out of proportion, hurts to swallow
• Tonsillar exudate (white pus on tonsils)
• Tender, swollen anterior cervical lymph nodes
• NO COUGH - this is the golden clue
• No runny nose - another clue
• Headache, malaise

• Tonsillar exudate
• Tender anterior cervical lymph nodes
• Fever history
• Absence of cough (1 point for no cough!)

• Penicillin V (500mg twice daily x 10 days) - first choice - cheap, narrow spectrum
• Amoxicillin (500mg twice daily x 10 days) - alternative first line, equally good
• If penicillin allergic: Azithromycin (500mg day 1, then 250mg days 2-5)
• NEVER amoxicillin if EBV mono is possible (causes a rash!)

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DISEASE 4: Infectious Mononucleosis (Mono / Glandular Fever)

1. Severe sore throat + tonsillar exudate (looks exactly like strep!)
2. Lymphadenopathy - especially posterior cervical nodes (strep affects anterior nodes)
3. Splenomegaly - enlarged spleen (important!)

• Extreme fatigue (can last weeks to months)
• Hepatitis (jaundice in 20-50%)
• Maculopapular rash (especially if given amoxicillin - classic exam question!)

• CBC: atypical lymphocytes (Downey cells)
• Monospot test (heterophile antibody) - positive in 95% of cases
• EBV-specific antibodies (VCA IgM) if monospot negative

• Supportive - rest, paracetamol for pain and fever
• No amoxicillin (causes florid rash)
• Steroids if severe airway obstruction from tonsillar swelling
• No contact sports for 6 weeks - spleen can rupture!
• Recover in 2-6 weeks usually - Textbook of Family Medicine

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DISEASE 5: Allergic Rhinitis (Hay Fever)

• Itchy nose, eyes, palate - itching is the hallmark (infections don't itch)
• Watery runny nose
• Sneezing in multiple sneezes in a row (paroxysmal sneezing)
• Red, watery eyes (conjunctivitis)
• Nasal congestion
• No sore throat (or very mild)
• No myalgia

1. "Does it happen every year at the same time (spring/summer)?" → Seasonal allergic rhinitis
2. "Does it happen when you're around cats, dogs, or dusty rooms?" → Perennial
3. "Does it itch?" → Allergy
4. "Have you had this exact thing 5 times before?" → Allergy, not infection

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DISEASE 6: Bacterial Sinusitis

• Facial pain/pressure/fullness over the cheeks (maxillary) or forehead (frontal)
• Pain worse on bending forward
• Unilateral maxillary pain and purulent discharge - very suggestive
• Thick, colored (yellow-green) nasal discharge persisting >10 days
• Reduced/lost sense of smell
• Dental pain (upper teeth share innervation with maxillary sinus)
• Symptoms lasting >10-14 days without improvement OR biphasic course (cold improves → then worsens)

• Most mild cases: still watchful waiting 3-5 days first (some resolve on their own)
• Moderate-severe: Amoxicillin-clavulanate (first line, 10-14 days)
• Penicillin allergy: trimethoprim-sulfamethoxazole or macrolides
• Adjuncts: saline nasal irrigation, intranasal steroids to reduce mucosal swelling

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DISEASE 7: COVID-19

• Loss of smell (anosmia) and/or taste (ageusia) - classic for COVID, rare in other URTIs
• Dry cough prominent
• Can range from mild cold-like to severe pneumonia
• Shortness of breath suggests lower respiratory involvement
• Fatigue can be prolonged ("long COVID")
• Test with rapid antigen test (RAT) or PCR

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THE MASTER DECISION FLOWCHART

Patient with runny nose / sore throat / cough / feeling unwell
                          │
         ┌────────────────┴─────────────────┐
         ▼                                  ▼
    FEVER present?                    NO FEVER
         │                                  │
    ┌────┴──────┐                  ┌────────┴────────┐
    ▼           ▼                  ▼                 ▼
 Sudden      Gradual         ITCHY nose/eyes?   No itch
 onset?      onset?          Seasonal pattern?       │
    │            │                │                  ▼
    ▼            ▼               YES           Common Cold
  FLU       Think:          Allergic          (if <10 days)
(myalgia   Strep/Mono/       Rhinitis
 severe)   COVID/Sinusitis
             │
     ┌───────┴──────────┐
     ▼                  ▼
  Tonsil          Extreme fatigue +
  exudate?        posterior nodes +
  No cough?       splenomegaly?
     │                  │
     ▼                  ▼
  Strep            Mono (EBV)
  (test it!)       (Monospot!)
             
             Symptoms >10 days?
             Facial pain?
                  │
                  ▼
            Bacterial Sinusitis

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ONE-LINE TREATMENT CHEAT SHEET

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EXAM TRIGGER PHRASES - MEMORIZE THESE

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