Respiratory Syncytial Virus

from https://www.ncbi.nlm.nih.gov/books/NBK459215/

• RSV: common virus infecting children and adults, especially the elderly.
• Common clinical presentation: upper respiratory infection, bronchiolitis in children.
• Severe cases: pneumonia, respiratory failure, apnea, death.
• Mainstay of treatment: supportive care.
• Passive immunization: available for at-risk children.
• Antiviral treatment: limited by efficacy, side effects, and cost.
• Interprofessional team: essential for management, care coordination, and improved outcomes.

Introduction

• RSV: widespread virus infecting children and elderly.
• Commonly presents: as upper respiratory infection; in young children, often causes bronchiolitis.
• Severe cases: can lead to pneumonia, respiratory failure, apnea, and death.
• Treatment: mainly supportive; passive preventive immunization available for at-risk children.
• Antiviral treatment: ribavirin, used on a case-by-case basis due to limited efficacy and high cost.

Etiology

• RSV: single-stranded RNA virus, Paramyxoviridae family, Pneumovirus genus.
• Discovered: in 1955 in chimpanzees, confirmed in humans shortly after.
• Structure: bilipid-layer envelope, ribonucleoprotein core, membrane proteins (attachment and fusion).
• Serotype and strains: one serotype, two strains (A and B) with structural protein variations.

Epidemiology

• Lack of long-term immunity: frequent reinfections.
• Infection rate: 90% of children within first 2 years.
• Lower respiratory tract illness: significant minority of cases, primarily bronchiolitis.
• High-risk groups: premature infants, cardiac, pulmonary, neurologic, immunosuppressive disorders, elderly.
• Global impact: 33 million lower respiratory tract illnesses, 3 million hospitalizations, up to 199,000 childhood deaths annually.
• Seasonal variation: winter-spring in temperate climates, less pronounced in tropical climates.

Pathophysiology

• Transmission: respiratory droplets.
• Incubation period: 2-8 days (mean 4-6 days).
• Target cells: apical ciliated epithelial cells in respiratory tract.
• Viral entry: RSV-G glycoprotein for attachment, RSV-F glycoprotein for fusion.
• Immune response: humoral and cytotoxic T-cell activation.
• Consequences: small airway obstruction, mucus plugging, ciliary dysfunction, airway edema, decreased lung compliance.

Histopathology

• Severe disease findings: abundant respiratory epithelial cell death, airway edema, immune cell infiltration (polymorphonuclear early, lymphomononuclear later).

History and Physical

• Upper respiratory illness: rhinorrhea, nasal congestion, cough, sneezing, fever, myalgia.
• Lower respiratory involvement: rhonchorous breath sounds, tachypnea, accessory muscle use, wheezes, prolonged expiration.
• Severe cases: viral pneumonia, hypoxia, lethargy, apnea, acute respiratory failure.

Evaluation

• Clinical diagnosis: no confirmatory testing required.
• Specific testing: rapid antigen and PCR testing.
  • Antigen testing: quick, inexpensive, specific, ~80% sensitivity.
  • PCR testing: more sensitive, can detect multiple organisms, higher cost, requires specialized equipment.
• Radiographic findings: hyperinflation, patchy atelectasis, peribronchial thickening.

Treatment / Management

• Supportive care:
  • Nasal suction and lubrication.
  • Antipyretics for fever.
  • Assisted hydration: oral, nasogastric tube, or intravenous.
  • Oxygen for hypoxia.
  • Ventilatory support: high-flow nasal cannula, CPAP, intubation, mechanical ventilation.
• Immune prophylaxis: palivizumab for at-risk infants.
  • Palivizumab: humanized murine monoclonal antibody, monthly administration during RSV season.
• Antiviral medication: ribavirin (case-by-case basis).
• Other treatments: albuterol, racemic epinephrine, steroids, hypertonic saline, antibiotics, chest physical therapy (not recommended).

Differential Diagnosis

• Asthma
• Bronchiolitis
• Influenza
• Croup
• Bronchitis
• Pneumonia

Prognosis

• Excellent outcome: for most children.
• Hospitalization: typically 3-4 days.
• High-risk infants: longer stays, higher rates of mechanical ventilation and ICU admission.
• Mortality: less than 1%, <400 deaths/year in the US.

Deterrence and Patient Education

• Hand washing: critical for prevention.
• Hygiene practices: avoid sharing drinks/utensils, clean surfaces, isolate infected individuals.

Pearls and Other Issues

• Severe RSV infection: increases risk for recurrent wheezing, childhood asthma, allergic sensitization.
• Palivizumab prophylaxis: may decrease incidence of recurrent wheezing.

Outcomes

• Majority of children: excellent outcome.
• High-risk infants: longer admissions, potential need for mechanical ventilation.
• Long-term: possible wheezing, but recent studies show no increased asthma risk

RSV immunisation

https://www.vaccinate.initiatives.qld.gov.au/what-to-vaccinate-against/rsv-immunisation

Medication Used: Nirsevimab (Brand Name: Beyfortus®)

• Type: Long-acting monoclonal antibody
• Protection Duration: At least 5 months
• Effectiveness: Up to 80% in decreasing infant hospitalisations related to RSV
• Approval: Determined safe and effective by Therapeutic Goods Administration (TGA) in November 2023

Program Commencement and Eligible Groups

• Eligibility: Only infants and young children who are residents of Queensland
  • Not required to be Medicare eligible
• Availability:
  • Queensland Birthing Hospitals (public and private): Starting 15 April 2024 for newborns
  • Other Immunisation Providers: Access via special-order process starting 22 April 2024

Program Focus

• Ensuring infants and young children at highest risk of severe RSV are protected due to global supply constraints.

Eligible Groups for RSV Immunisation

1. All infants born on or after 1 February 2024
   • At birth or prior to discharge from hospital
   • Not immunised in hospital: Access nirsevimab up to less than 8 months of age through primary care providers
   • Ineligible once they reach 8 months of age
2. Aboriginal and Torres Strait Islander infants less than 8 months of age
   • Eligible even if born prior to the program commencement, if they receive nirsevimab before reaching 8 months of age
   • Ineligible once they reach 8 months of age
3. Infants with certain complex medical conditions from birth to less than 8 months of age*
   • Eligible if born prior to the program commencement and receive nirsevimab before reaching 8 months of age
   • Ineligible once they reach 8 months of age
4. Young children with certain complex medical conditions from 8 months to less than 20 months of age, until 31 October 2024*
   • Time-limited: Doses available until 31 October 2024
   • Ineligible once they reach 20 months of age
   • Restricted stock due to the specialised nature of this cohort and supply constraints

Eligible Complex Medical Conditions*

• Prematurity: Born less than 32 weeks gestation and less than 12 months of age
• Chronic Neonatal Lung Disease: Neonates requiring home oxygen/other respiratory support, less than 20 months of age
• Significant Respiratory Conditions: Requiring respiratory support such as tracheostomy, non-invasive ventilation (BIPAP or CPAP), or cystic fibrosis with severe lung disease or weight for length less than 10th percentile, less than 20 months of age
• Congenital Heart Disease: Haemodynamically significant, less than 20 months of age
• Severe Primary Immunodeficiency: Less than 20 months of age and not yet received curative treatment
• Trisomy 21: Less than 20 months of age
• Post Solid-Organ Transplant or End Stage Organ Disease: Awaiting transplant, less than 20 months of age
• Active Chemotherapy: Infants less than 20 months of age
• HSCT: Infants less than 20 months of age within 28 days prior to HSCT or prior to engraftment post HSCT
• Neuromuscular Disorders: Associated with significantly impaired respiratory function such as spinal muscular atrophy (SMA), less than 20 months of age
• Other Infants: Less than 20 months of age by exception only, with complex medical conditions after discussion with a Paediatric Infectious Diseases Specialist

Notes

• Clinical Guidance for Immunisation Service Providers: Refer for infants born to a person who received RSV vaccination during pregnancy.
• Special-order Process: Available for other immunisation providers starting 22 April 2024.