Complications

Complications table
ComplicationTimeframeLikelihood

bacterial pneumonia

short termhigh

Most commonly occurs in high-risk populations, such as those with chronic medical conditions, and is associated with 25% of all influenza deaths.[93] An estimated 11.5% of lower respiratory tract infections (LRTI) are caused by seasonal influenza. Adults aged over 70 years are particularly susceptible to influenza LRTIs.[154]

The most common organisms involved are Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae.[155]

Treat with antibiotics that provide coverage against these bacterial organisms or as indicated by culture results.

Chest x-ray will reveal typical infiltrates.

viral pneumonia

short termlow

Primary influenza pneumonia occurs when influenza virus infection directly involves the lung tissue. An estimated 11.5% of lower respiratory tract infections (LRTI) are caused by seasonal influenza. Adults aged over 70 years are particularly susceptible to influenza LRTIs, which caused an estimated 9,459,000 hospitalisations and 145,000 deaths globally in 2017.[154]

Suspicion should be raised when symptoms persist and increase instead of resolving in a patient with acute influenza.

High fever, dyspnoea, and even progression to cyanosis can be seen.[4]

Most commonly occurs in high-risk populations, such as those with chronic medical conditions.

otitis media

short termlow

Complicates the course of influenza in 10% to 50% of children.[156] Treatment with oseltamivir reduces the incidence of new acute otitis media infections in children.[157]

Aetiology is a bacterial superinfection most commonly associated with Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis.[158] Treatment is based on coverage for these organisms.

rhabdomyolysis/myositis

short termlow

Reported more frequently in children, myositis typically presents as sore muscles of the legs.

The pathogenesis is not well understood; however, the presence of influenza virus in affected muscles has been noted.[159]

Characterised by increased levels of creatine phosphokinase in serum and, possibly, myoglobinuria with renal failure.[160][161]

encephalitis

short termlow

A retrospective cohort study of 842 children in the US with laboratory-confirmed influenza in the years between 2000 and 2004 found the incidence of neurological complications was 4 cases per 100,000 person-years.[156]

Neurological complications were more frequent for ages 6 months to 4 years and in those with underlying neurological or neuromuscular disease.

Encephalitis occurs when the virus enters the CNS. Since abnormalities in brain function are common in encephalitis, monitor for altered mental status, motor or sensory deficits, altered behaviour and personality changes, and speech or movement disorders.

Treatment is supportive.

transverse myelitis

short termlow

This is a segmental spinal cord injury caused by acute inflammation. Typically the inflammation is bilateral, producing weakness and sensory disturbance below the level of the lesion.

MRI of the spinal cord shows gadolinium-enhancing signal abnormality in the affected segment(s).

Patients are often treated with parenteral corticosteroids.[162]

aseptic meningitis

short termlow

Patients with meningitis may be uncomfortable, lethargic, and/or distracted by headache, but their cerebral function remains normal.

Treatment is supportive.

A retrospective cohort study of 842 children in the US with laboratory-confirmed influenza in the years between 2000 and 2004 found the incidence of neurological complications was 4 cases in 100,000 person-years.[156] Neurological complications were more frequent for ages 6 months to 4 years and in those with underlying neurological or neuromuscular disease.

Guillain-Barre syndrome (GBS)

short termlow

A heterogeneous condition with several variant forms. Most often, GBS presents as an acute paralysing illness provoked by a preceding infection.

The cardinal clinical features of GBS are progressive, fairly symmetrical muscle weakness accompanied by absent or depressed deep tendon reflexes.

Treatment is mostly supportive, although disease-modifying agents such as corticosteroids and immunoglobulin infusions have been used.[163]

toxic shock syndrome

short termlow

Toxic shock syndrome, associated with Staphylococcus aureus infection and acute influenza, has been described after both influenza A and B infections in case reports.[164]

post-influenza encephalopathy

long termlow

A retrospective cohort study of 842 children in the US with laboratory-confirmed influenza in the years between 2000 and 2004 found the incidence of neurological complications was 4 cases in 100,000 person-years.[156]

Neurological complications were more frequent for ages 6 months to 4 years and in those with underlying neurological or neuromuscular disease.

Monitor for altered mental status, motor or sensory deficits, altered behaviour and personality changes, and speech or movement disorders.

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