Seasonal Influenza

Antimicrobial prescribing: NHS Lothian
NHS Lothian

Seasonal Influenza A and B generally circulate from November through to spring but may be seen out of season, particularly in patients returning from the southern hemisphere (their winter) and tropical regions (where influenza is found throughout the year).

Assessment

Influenza can be divided into uncomplicated or complicated infection.

Uncomplicated influenza: fever, coryza, generalised symptoms (headache, malaise, myalgia, arthralgia) and sometimes gastrointestinal symptoms, but without any features of complicated influenza.

Complicated influenza: requiring hospitalisation, with or without evidence of lower respiratory tract infection (hypoxaemia, dyspnoea, lung infiltrate), central nervous system involvement, and/or a significant exacerbation of an underlying medical condition

All patients with complicated influenza should be assessed for treatment, irrespective of onset of symptoms, unless there is clear evidence of recovery.

Risk factors for complicated influenza include:

  • neurological, hepatic, renal, pulmonary and chronic cardiac disease
  • diabetes mellitus
  • severe immunosuppression
  • age over 65 years
  • pregnancy (including up to 2 weeks post-partum)
  • children under 6 months of age
  • morbid obesity (BMI ≥40)

Required investigations

Testing is by respiratory virus PCR on combined nose & throat swab (‘Resp virus screen’), or sputum (‘Respiratory sputum’).

Treatment recommendations

Recommended total duration: 5 days (10 days for patients with severe immunosuppression)

Oseltamivir 75mg 12 hours orally

Can be given NG if required 

Please refer to national guidance  “Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza” for full details on treatment,  including dosing in renal impairment, extremes of weight and second line options.

Where there is a high index of suspicion of oseltamivir resistance (e.g. treatment failure, infection occurs following prophylaxis, exposure to oseltamivir resistant flu A) OR known oseltamivir resistance, zanamivir should be used – this should be following discussion with virology.

 

Prophylaxis of Influenza

Patients exposed to influenza who are unvaccinated or unprotected (those vaccinated less than 14 days prior to exposure) and who are in a high risk group (see 'Assessment' guidance) should be assessed for symptoms of current infection, and offered prophylaxis if asymptomatic.

If symptoms are present, follow ‘ Treatment recommendations ’ guidance.

Prophylaxis should be within 48 hours of last exposure – or later on further discussion with virology.

Recommended total duration: 10  days 

Oseltamivir 75mg 24 hours orally

Can be given NG if required 

Please refer to national guidance “Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza” for full details on dosing, including dosing in renal impairment, extremes of weight and second line options.

 

 

Notes

Risk assessment for avian influenza should be done for patients with influenza-like illness, and in the 10 days before the onset of symptoms have a history of close contact (within 1m) with live, dying or dead domestic poultry or wild birds, including live bird markets, in an area of the world affected by avian influenza or with any confirmed infected animal. See UKHSA guidance for further information.

Unvaccinated eligible patients with one type of flu should be encouraged to still receive flu vaccine to provide protection against other flu types.