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Microbiology

Respiratory

This section will cover major respiratory pathogens, such as influenza virus, RSV, parainfluenza virus, and SARS-CoV-2 - focusing on their etiology, epidemiology, transmission, and the diseases they cause

Etiology, Epidemiology, Transmission, and Disease States

Influenza Virus

  • Etiology
    • Types: Influenza viruses are classified into types A, B, C, and D
    • Influenza A: Further classified into subtypes based on two surface glycoproteins: hemagglutinin (H) and neuraminidase (N). Examples include H1N1 and H3N2
    • Influenza B: Not classified into subtypes but can be further divided into lineages
    • Influenza C: Causes mild respiratory illness, not typically associated with epidemics
    • Influenza D: Primarily affects cattle, not known to cause illness in humans
  • Epidemiology
    • Seasonality: Typically occurs during the fall and winter months in temperate climates
    • Global Distribution: Found worldwide
    • Age Groups: Affects all age groups but can be more severe in young children, the elderly, and individuals with underlying health conditions
    • Pandemics: Influenza A viruses have caused several pandemics, including the 1918 Spanish flu (H1N1), the 2009 swine flu (H1N1), and others
  • Transmission
    • Respiratory Droplets: Primarily spread through respiratory droplets produced when infected individuals cough, sneeze, or talk
    • Contact: Can also be transmitted through direct or indirect contact with contaminated surfaces
  • Disease States
    • Influenza (Flu): Characterized by fever, cough, sore throat, muscle aches, fatigue, and headache
    • Complications: Pneumonia (viral or secondary bacterial), bronchitis, sinus infections, ear infections, and exacerbation of chronic medical conditions (e.g., asthma, heart failure)
    • High-Risk Groups: Severe illness and complications are more common in young children, older adults, pregnant women, and individuals with chronic medical conditions

Respiratory Syncytial Virus (RSV)

  • Etiology
    • Classification: A member of the Paramyxoviridae family
    • Types: Two major antigenic subgroups, A and B
  • Epidemiology
    • Seasonality: Typically occurs during the fall and winter months
    • Ubiquitous: Extremely common, with most children infected by age 2
    • Age Groups: Primarily affects infants and young children, but can also cause illness in older adults and immunocompromised individuals
  • Transmission
    • Respiratory Droplets: Spread through respiratory droplets produced when infected individuals cough or sneeze
    • Contact: Can also be transmitted through direct or indirect contact with contaminated surfaces
  • Disease States
    • Bronchiolitis: Inflammation of the small airways in the lungs, primarily affecting infants
    • Pneumonia: Infection of the lungs
    • Common Cold-like Symptoms: In older children and adults, RSV can cause mild upper respiratory symptoms such as runny nose, cough, and sore throat
    • High-Risk Groups: Premature infants, young children with congenital heart or lung disease, and immunocompromised individuals are at higher risk for severe RSV infection

Parainfluenza Virus (PIV)

  • Etiology
    • Classification: A member of the Paramyxoviridae family
    • Types: Four types: PIV-1, PIV-2, PIV-3, and PIV-4
  • Epidemiology
    • Seasonality: PIV-1 and PIV-2 typically occur in the fall, while PIV-3 has a less predictable seasonal pattern
    • Age Groups: Primarily affects infants and young children
  • Transmission
    • Respiratory Droplets: Spread through respiratory droplets produced when infected individuals cough or sneeze
    • Contact: Can also be transmitted through direct or indirect contact with contaminated surfaces
  • Disease States
    • Croup (Laryngotracheobronchitis): Characterized by a barking cough, stridor (a high-pitched breathing sound), and hoarseness. Primarily caused by PIV-1 and PIV-2
    • Bronchiolitis and Pneumonia: Can also cause lower respiratory tract infections, especially PIV-3
    • Common Cold-like Symptoms: In older children and adults, PIV can cause mild upper respiratory symptoms

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2)

  • Etiology
    • Classification: A member of the Coronaviridae family
    • Variants: Multiple variants have emerged, including Alpha, Beta, Delta, Omicron, and their subvariants, each with different transmissibility and severity
  • Epidemiology
    • Pandemic: Caused the COVID-19 pandemic, with global spread
    • Age Groups: Affects all age groups, but older adults and individuals with underlying health conditions are at higher risk for severe illness
  • Transmission
    • Respiratory Droplets and Aerosols: Primarily spread through respiratory droplets and aerosols produced when infected individuals cough, sneeze, talk, or breathe
    • Contact: Can also be transmitted through direct or indirect contact with contaminated surfaces, although this is less common
  • Disease States
    • COVID-19: Ranges from asymptomatic infection to severe illness and death
    • Symptoms: Fever, cough, fatigue, loss of taste or smell, sore throat, headache, muscle aches, shortness of breath, and gastrointestinal symptoms
    • Complications: Pneumonia, acute respiratory distress syndrome (ARDS), blood clots, multisystem inflammatory syndrome in children (MIS-C), long-term symptoms (long COVID)
    • High-Risk Groups: Older adults, individuals with chronic medical conditions (e.g., heart disease, diabetes, obesity), and immunocompromised individuals are at higher risk for severe COVID-19

Important Notes

  • Prevention: Vaccination is available for influenza and COVID-19. RSV vaccines and monoclonal antibody prophylaxis are available for certain high-risk infants
  • Diagnosis: Respiratory viruses are typically diagnosed using molecular methods (e.g., PCR) on nasopharyngeal swabs or other respiratory specimens
  • Treatment: Antiviral medications are available for influenza (e.g., oseltamivir, zanamivir) and COVID-19 (e.g., remdesivir, nirmatrelvir/ritonavir). Supportive care is important for all respiratory viral infections

Key Terms

  • Etiology: The cause or origin of a disease or condition
  • Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems
  • Transmission: The way a disease is spread from one person or source to another
  • Respiratory Droplets: Small particles produced when an infected person coughs, sneezes, talks, or breathes
  • Aerosols: Even smaller particles that can remain suspended in the air for longer periods and travel greater distances
  • Bronchiolitis: Inflammation of the small airways in the lungs
  • Croup: Inflammation of the larynx and trachea, causing a barking cough
  • Stridor: A high-pitched, noisy breathing sound
  • Variants: Different versions of a virus with genetic mutations that can affect transmissibility, severity, or immune evasion
  • ARDS (Acute Respiratory Distress Syndrome): A severe lung condition characterized by widespread inflammation and fluid buildup in the lungs
  • MIS-C (Multisystem Inflammatory Syndrome in Children): A rare but serious condition associated with COVID-19, characterized by inflammation of multiple organ systems