323.1 🎓 醫孞生版

323.1.0.1 📌 䞀頁重點

323.1.0.1.1 Influenza Pneumonia
323.1.0.1.1.1 Etiology
  • Influenza A (more severe, pandemic potential): H1N1, H3N2 currently circulating
  • Influenza B: seasonal, less severe usually
  • Influenza C: mild
  • Influenza D: cattle (no human disease yet)
323.1.0.1.1.2 Antigenic Variation
  • Antigenic drift: minor mutations, seasonal
  • Antigenic shift: major reassortment, pandemic (H1N1 2009)
  • Mutation rate ↑ in RNA virus
323.1.0.1.1.3 Epidemiology
  • Seasonal (winter Northern hemisphere, Oct-May)
  • ~ 290,000-650,000 deaths globally per year
  • Vulnerable: elderly, very young, pregnant, immunocompromised, chronic disease
323.1.0.1.1.4 Clinical
  • Acute onset: fever, chills, myalgia, headache, dry cough, sore throat, runny nose
  • Respiratory symptoms: cough, dyspnea
  • Severe: viral pneumonia, ARDS, bacterial superinfection (S. aureus, S. pneumoniae)
  • Extrapulmonary: myocarditis, encephalitis, GBS
323.1.0.1.1.5 Diagnosis
  • RT-PCR (molecular, gold standard)
  • Rapid antigen tests (less sensitive)
  • Direct fluorescent antibody (DFA)
  • Multiplex PCR panels
323.1.0.1.1.6 Treatment
  • Oseltamivir (Tamiflu) 75 mg BID × 5 days
    • Start within 48 hours of symptom onset (most benefit)
    • Severe / hospitalized: start even after 48 hours
    • Pediatric formulations available
  • Zanamivir (Relenza) — inhaled
  • Peramivir (Rapivab) — IV (single dose, severe)
  • Baloxavir (Xofluza) — single oral dose; CAP-IT trial
  • Combination oseltamivir + baloxavir for severe (RCTs ongoing)
323.1.0.1.1.7 Prevention
  • Annual influenza vaccine (October-November optimal)
  • Types: inactivated (IIV), live attenuated (LAIV), recombinant
  • Antiviral prophylaxis for high-risk exposure
  • Hand hygiene, masking, isolation
323.1.0.1.1.8 Bacterial Superinfection
  • Post-influenza pneumonia
  • S. aureus (often MRSA, including PVL+), S. pneumoniae, H. influenzae, GNR
  • Severe, cavitating
  • Vancomycin + standard CAP coverage
323.1.0.1.2 Respiratory Syncytial Virus (RSV)
323.1.0.1.2.1 Epidemiology
  • Most common cause of lower respiratory infection in infants
  • Also serious in: elderly, immunocompromised, transplant
  • Seasonal (winter), worldwide
323.1.0.1.2.2 Clinical
  • Bronchiolitis in infants
  • Pneumonia in adults
  • Exacerbation of COPD, asthma, HF
  • Dyspnea, wheeze, cough
  • Severe: respiratory failure, ARDS
323.1.0.1.2.3 Diagnosis
  • RT-PCR
  • Multiplex respiratory PCR panels
323.1.0.1.2.4 Treatment
  • Supportive (oxygen, hydration, bronchodilators)
  • Ribavirin — limited efficacy, used in transplant patients
  • Palivizumab — monoclonal antibody, prophylaxis in high-risk infants
323.1.0.1.2.5 Prevention (2023-2024 NEW)

RSV Vaccines for Adults ≥ 60: - Arexvy (GSK, RSV-pre-F adjuvanted) - Abrysvo (Pfizer, bivalent RSV) - Reduces hospitalization 70-80% (1-2 seasons)

Maternal RSV Vaccine (Abrysvo): - 32-36 weeks gestation - Protects infant 0-6 months

Nirsevimab (Beyfortus, 2023 FDA): - Long-acting monoclonal antibody - Single dose for infants - Protects through first RSV season - Replaces / supplements palivizumab

323.1.0.1.3 COVID-19 (SARS-CoV-2)
323.1.0.1.3.1 Background
  • Emerged Wuhan 2019; pandemic declared 2020
  • Multiple variants (Alpha, Beta, Delta, Omicron sublineages)
  • Ongoing endemic
323.1.0.1.3.2 Clinical Spectrum
  • Asymptomatic
  • Mild (URI symptoms, anosmia/ageusia)
  • Moderate (pneumonia)
  • Severe (hypoxemia, ARDS, MOF)
  • Long COVID (PASC — post-acute sequelae)
323.1.0.1.3.3 Diagnosis
  • RT-PCR (gold standard)
  • Rapid antigen tests
  • Serology for past infection (not acute diagnosis)
323.1.0.1.3.4 Risk Factors for Severe COVID-19
  • Age (highest ≥ 75)
  • Unvaccinated / under-vaccinated
  • Immunocompromise
  • Cardiovascular disease
  • Diabetes
  • Obesity
  • Chronic lung disease
  • Pregnancy (esp third trimester)
  • CKD
  • Cancer
323.1.0.1.3.5 Treatment

Outpatient (Mild-Moderate, High-Risk): - Nirmatrelvir/ritonavir (Paxlovid) within 5 days - Most effective - Drug interactions - Remdesivir IV × 3 days - Molnupiravir (less effective; pregnancy contraindicated) - Monoclonal antibodies (variant-dependent; many obsolete vs Omicron)

Inpatient (Hospitalized): - Dexamethasone 6 mg/d × 10 days if requires O2 (RECOVERY 2020) - Remdesivir for those on supplemental O2 (not HFNC/ventilator initially) - Baricitinib (REMAP-CAP, COV-BARRIER) for severe + on O2 - Tocilizumab (REMAP-CAP) for severe + on O2 + ↑ inflammatory markers - Anticoagulation (therapeutic for moderate; prophylactic for severe — INSPIRATION, ATTACC, ACTIV-4a)

ICU: - Mechanical ventilation if needed - Prone positioning - ECMO for refractory

323.1.0.1.3.6 Long COVID (PASC)
  • 10-30% of survivors
  • Persistent dyspnea, fatigue, cognitive impairment, palpitations
  • Microvascular dysfunction, autoimmune, inflammation
  • Multidisciplinary care
  • No specific antiviral
  • Various therapies emerging
323.1.0.1.3.7 Prevention
  • Vaccines: mRNA (Pfizer, Moderna), protein-based (Novavax), updated annually
  • Boosters for high-risk
  • Masking in healthcare + crowded indoor (selective)
  • Hand hygiene
323.1.0.1.4 Other Viral Pneumonias
323.1.0.1.4.1 Adenovirus
  • Wide range of severity
  • Outbreaks in military, dormitories, hospitals
  • Multiple serotypes
  • Cidofovir for severe (off-label)
323.1.0.1.4.2 Parainfluenza Virus
  • Croup in children
  • Lower respiratory infection
  • Immunocompromised: severe
323.1.0.1.4.3 Human Metapneumovirus
  • Similar to RSV
  • Older adults + immunocompromised
  • Supportive treatment
323.1.0.1.4.4 Rhinovirus
  • Most common URI
  • Can cause LRT infection in elderly + COPD/asthma
323.1.0.1.4.5 Coronaviruses (Non-SARS, Non-MERS)
  • Common cold viruses
  • 229E, OC43, NL63, HKU1
  • Most mild
323.1.0.1.4.6 MERS-CoV (Middle East Respiratory Syndrome)
  • Middle East, camels
  • Severe pneumonia + ARDS
  • High mortality (~ 35%)
  • Supportive
323.1.0.1.4.7 Measles + Varicella
  • Vaccination-related decline
  • Measles can cause giant cell pneumonia (immunocompromised, children)
  • Varicella in adults: hemorrhagic pneumonia, severe
323.1.0.1.4.8 Hantavirus
  • Rodent exposure (Sin Nombre, US Southwest)
  • Hantavirus Pulmonary Syndrome (HPS)
  • High mortality (~ 30-40%)
  • Aggressive supportive care, no specific antiviral
323.1.0.1.5 Bacterial Co-Infection / Superinfection

323.1.1 High-Risk Setting:

  • Post-influenza (top: S. aureus, S. pneumoniae)
  • COVID-19 (lower than thought; Aspergillus + bacterial)
  • RSV in elderly
  • Adenovirus

323.1.2 Diagnosis:

  • Worsening after initial improvement
  • Persistent / recurrent fever
  • New leukocytosis
  • New infiltrate or expansion
  • Procalcitonin elevation

323.1.3 Treatment:

  • Broad-spectrum antibiotics
  • Cover S. aureus (vanc/linezolid) + S. pneumoniae

323.1.3.1 🩺 床邊速查

  • Influenza diagnosis: RT-PCR (gold standard); seasonal late fall-early spring
  • Treatment: oseltamivir 75 BID × 5 d (within 48 hr ideal)
  • Baloxavir: single oral dose alternative
  • RSV adults ≥ 60: vaccines Arexvy/Abrysvo 2023 NEW
  • RSV infants: nirsevimab (Beyfortus, 2023 FDA)
  • COVID outpatient: Paxlovid (nirmatrelvir/ritonavir) within 5 d
  • COVID severe: dexamethasone 6 mg × 10 d (RECOVERY); tocilizumab/baricitinib (REMAP-CAP)
  • Post-influenza pneumonia: S. aureus (often MRSA), vancomycin