Incubation period 1-4 days. Infectious period from day before symptoms appear, to 5 days after symptoms appear.  Virus shedding can persist for months in immunocompromised (as other viruses).

Main types A and B.  B shows antigenic drift, with minor variations over time.  A shows antigenic shift, with appearance of new N type usually associated with global pandemic eg Spanish flu.

Case definition

At least one of these systemic symptoms: Fever (or feverishness), malaise, headache, myalgia;

PLUS at least one of these respiratory symptoms: cough, sore throat (!), shortness of breath.

Transmission

• Large droplet eg sneezing, range only a metre or so.
• Direct/indirect contact eg sneezing into hands, and then to surfaces.  Survive at least 24 hrs in environment.
• Aerosol generating procedures can produce small droplets with further range (how far?).  Includes intubation, extubation, open suctioning, CPAP/HFOV/BiPAP, CPR.  NOT high flow O2 or nebs.

Prevention is therefore by good hygiene viz covering nose and mouth during coughing/sneezing, wiping with disposable tissues, avoiding touching nose/eyes/mouth, washing hands (alcohol gel adequate if hands visibly clean); and immunisation.

For close patient contact, aprons, masks, gloves recommended.  Similarly, consider eye protection.

For aerosol generating procedures, FFP3 (filter face piece, efficiency grade 3) masks required.  Such masks can be worn for up to 8 hours if necessary.  Fluid repellent gowns if extensive secretions or bodily fluids anticipated.

High risk

Long list of people at higher risk eg chronic cardiac/respiratory conditions.  Includes pregnant women.  See Green book on immunizations.

Treatment

See Influenza treatment.