- Explain selected features of influenza biology and viral structures.
- Interpret the presented patterns of seasonality and disease burden.
- Distinguish diagnostic, treatment, prophylaxis, and public-health priorities.
- Apply supported recommendations to clinical and residential-care scenarios.
Influenza Biology and Ecology
The viral envelope makes influenza susceptible to soap and water and to alcohol hand gels.
Influenza viruses undergo continual antigenic mutation. Influenza's genetic instability and continual change require repeated updates to vaccine formulations.
- Water birds in Southeast Asia are the normal hosts of influenza viruses.
- Some animal strains reach humans through pigs, while avian strains can pass directly from birds into humans.
- After crossing into humans, a strain may adapt and become a circulating human virus.
What feature makes influenza susceptible to soap and water and to alcohol hand gels?
Its viral envelope.
Viral Structures and Influenza Types
- Hemagglutinin enables an influenza particle to attach to a host cell.
- Neuraminidase helps newly produced particles leave infected respiratory epithelial cells.
- The M2 ion channel helps stabilize influenza particles, particularly as they leave cells.
Influenza A viruses are classified by hemagglutinin and neuraminidase types. Influenza B viruses are described by lineages such as Victoria and Yamagata.
Which structure should you identify when asked how newly produced influenza particles leave infected respiratory epithelial cells?
Neuraminidase.
Seasonality and Disease Burden
Influenza is predominantly a winter infection in temperate regions. In tropical regions, circulation generally tends to occur throughout the year.
For most Australian seasons in the data discussed, influenza seasons commonly began around June or July and peaked around September.
How do the presented temperate and tropical circulation patterns differ?
Influenza is predominantly a winter infection in temperate regions, while circulation in tropical regions generally tends to occur throughout the year.
Diagnosis and Clinical Treatment Priorities
- A clearly measurable serologic antibody response generally may take about two weeks after infection.
- Serology cannot distinguish antibodies produced by vaccination from antibodies produced by infection.
- Viral culture is not routinely used for diagnosis and is now largely confined to reference laboratories.
Nucleic acid testing of a throat swab can provide a rapid result and distinguish influenza A from influenza B. Reference laboratories can subtype strains beyond that A-or-B result.
Supportive care is the main clinical management for most people with influenza. Prompt neuraminidase-inhibitor treatment is recommended for hospitalized patients with confirmed or suspected influenza and for people at increased risk of complications.
Which described test can rapidly distinguish influenza A from influenza B using a throat swab?
Nucleic acid testing.
Antiviral Treatment and Evidence
Amantadine acts on the M2 ion channel rather than neuraminidase, but influenza strains developed resistance to amantadine rapidly.
Neuraminidase inhibitors prevent influenza particles from being released from infected cells.
- Treatment works best when started within the first 24 hours.
- Treatment has clinical benefit when begun within 48 hours.
- Neuraminidase inhibitors reduce symptoms but do not cure influenza.
A neuraminidase inhibitor is started 36 hours after symptoms begin. What supported timing statement applies?
Treatment has clinical benefit when begun within 48 hours, although it works best when started within the first 24 hours.
Antiviral Prophylaxis and Residential Outbreaks
Neuraminidase-inhibitor prophylaxis significantly reduces the risk of symptomatic influenza. It should be considered for high-risk contacts of a confirmed case, but it is not an alternative to vaccination.
When a household contains both an influenza case and a high-risk person, oseltamivir prophylaxis is recommended for every other household member.
A household has one influenza case and one high-risk person. Who else is recommended to receive oseltamivir prophylaxis?
Every other household member.
Public Health Management and Surveillance
Vaccination is the most effective influenza-prevention measure, although it is not perfect.
- Testing provides case numbers needed for surveillance.
- Surveillance requires information about circulating subtypes.
- Subtype data inform vaccine development and show whether circulating strains match the vaccine.
- Testing can alert public health authorities to an emerging pandemic strain.
Point-of-care testing can enable earlier influenza diagnosis without waiting about a day for a laboratory result.
How can circulating-subtype data support both vaccine work and assessment of the current vaccine?
The data inform vaccine development and show whether circulating strains match the vaccine.
Common misconceptions
Watch out: Antibacterial drugs specifically treat influenza virus infection.
Instead: Antibacterial drugs do not provide specific treatment for influenza virus infection.
Watch out: Neuraminidase inhibitors cure influenza.
Instead: They do not cure influenza, although they reduce symptoms.
Watch out: A negative point-of-care result necessarily excludes influenza.
Instead: For the tests discussed, a negative point-of-care result does not necessarily exclude influenza.
Lesson recap
- Influenza undergoes continual antigenic mutation, and its genetic instability and continual change require repeated vaccine-formulation updates.
- Supportive care is the main management for most people, while prompt neuraminidase-inhibitor treatment is recommended for hospitalized patients with confirmed or suspected influenza.
- During a residential-care outbreak, antiviral prophylaxis is recommended in addition to infection-control measures.
- Testing supplies case numbers and subtype information for influenza surveillance.