Severe Influenza

Influenza, colloquially known as ‘the flu’, is a common infectious disease caused by one of three influenza viruses – A, B or C. 

While early stage influenza can be indistinguishable from the common cold, and modern medicine has become incredibly efficient at diagnosing and treating the condition, influenza still has the ability to develop rapidly, endangering infected individuals if left unchecked.

Severe influenza presents unique challenges for clinicians. While mild influenza can be treated via ambulatory care, patients who develop complications could get severe influenza which can result in hospital and even ICU admission. Infants, the elderly and sufferers of chronic disease are most at risk of severe influenza, as it can result in complications and exacerbations of underlying conditions([FOOTNOTE=Choi WS, Baek JH, Seo YB, et al. Severe influenza treatment guideline. The Korean Journal of Internal Medicine. 2014;29(1):132-147. doi:10.3904/kjim.2014.29.1.132.],[ANCHOR=],[LINK=]). In the UK, children under 5 have the highest influenza admission rate (1.9 per 1000), while over two-thirds (72%) of all influenza-attributable deaths in hospital occurred in patients over the age of 65 who had co-morbidities.([FOOTNOTE=Cromera D, Jan van Hoek A, Jit M, Edmunds WJ, Fleming D, Miller E. The burden of influenza in England by age and clinical risk group: A statistical analysis to inform vaccine policy. Journal of Infection, Vol 68, Issue 4. April 2014, Pages 363-371. doi: 10.1016/j.jinf.2013.11.013],[ANCHOR=],[LINK=])

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Symptoms and Risk Factors

According to World Health Organisation (WHO) guidelines([FOOTNOTE=World Health Organization. WHO guidelines for pharmacological management of pandemic (H1N1) 2009 influenza and other influenza viruses [Internet] Geneva (CH): World Health Organization; c2013. Available from:],[ANCHOR=],[LINK=]), severe influenza is defined as a positive influenza test result combined with at least one of the following clinical presentations:

  • Dyspnoea, tachypnoea, or hypoxia
  • Radiological signs of lower respiratory tract disease
  • Central nervous system involvement (e.g., encephalopathy, encephalitis)
  • Severe dehydration
  • Acute renal failure
  • Septic shock
  • Exacerbation of underlying chronic disease, including asthma, chronic obstructive pulmonary disease (COPD), chronic hepatic or renal insufficiency, diabetes mellitus, or other cardiovascular conditions
  • Any other influenza-related condition or clinical presentation requiring hospital admission

Risk factors for severe influenza could include chronic respiratory, renal, liver, and heart diseases. Also aged patients, are at higher risk just like obese persons (in particular morbid obese >40 body mass index). And finally it seems that pregnancy, particularly the third trimester, can also increase the risk of complications.([FOOTNOTE=Van Kerkhove, M.D., Vandemaele, K.A.H., et al. Risk Factors for Severe Outcomes following 2009 Influenza A (H1N1) Infection: A Global Pooled Analysis. PLoS Med 8(7): e1001053],[ANCHOR=],[LINK=])


There are several influenza tests that offer almost instant positive or negative results.

The most common are rapid influenza diagnostic tests (RIDTs) which detect influenza antigens. These tests produce results within 10-15 minutes([FOOTNOTE=],[ANCHOR=],[LINK=]) but are not entirely accurate. Rapid molecular assays swab and analyse respiratory tract mucus and are more accurate than RIDTs, but take longer to produce results (15-20 minutes)([FOOTNOTE=],[ANCHOR=],[LINK=]). These tests, in concert with physical examination, are generally enough for a clinician to confidently diagnose influenza.


Upon admission into hospital, anti-viral medications such as Oseltamivir are effective in treating the influenza, and in severe cases may need to be administered for longer than the usual treatment duration.([FOOTNOTE=Rouleau I, Charest H, Douville-Fradet M, et al. Field performance of a rapid diagnostic test for influenza in an ambulatory setting. J. Clin. Microbiol. 2009;47:2699 –2703. 10.1128/JCM.00762-09.],[ANCHOR=],[LINK=])

As severe influenza can present in the wide variety of ways listed above, a patient’s treatment will focus on minimising symptoms, and will be guided by their clinical presentations. Antibiotics may be administered if the patient has accompanying pneumonia, sinusitis or any other bacterial infection, and various treatments aiming to oxygenate the body may be employed if the patient presents with pulmonary issues. How these treatments might interact with the antiviral medications must be carefully considered before being prescribed.([FOOTNOTE=Leekha S, Zitterkopf NL, Espy MJ, et al. Duration of influenza A virus shedding in hospitalized patients and implications for infection control. Infect Control Hosp Epidemiol. 2007; 28(9):1071-6.],[ANCHOR=],[LINK=])


Discover below which pulse oximeters from Medtronic can help treating patients who have been diagnosed with severe influenza. 

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