HOW TO TREAT 27
ausdoc . com . au 14 MARCH 2025
HOW TO TREAT 27
Box 1 . Individuals at higher risk of poor outcomes from influenza *
• Adults 65 or older .
• Pregnant women or those up to two weeks postpartum .
• People with : — Heart disease . — Down syndrome . — Obesity ( BMI 30kg / m 2 or more ). — Chronic respiratory conditions . — Severe neurological conditions . — Immune compromise . — Other chronic illnesses .
• Aboriginal and Torres Strait Islander people of any age .
• Children aged five or younger , but especially less than two . #
• Residents of aged care facilities or long-term residential facilities .
• Homeless people . * Higher-risk groups may vary with different strains of influenza .
#
In young children , rates of hospitalisation and mortality are greatest among those younger than six months . Sources : Therapeutic Guidelines Antibiotic 29 , US Centers for Disease Control and Prevention 2023 30
non-localising rales , rhonchi or wheeze . 7 Crackles or decreased breath sounds on chest examination may suggest complications , such as viral pneumonia , secondary bacterial pneumonia or heart failure . 16
PROGNOSIS
MOST people with influenza recover without serious complications or sequelae .
Specific groups at higher risk of poor outcomes from influenza-associated complications , severe influenza and hospitalisation or death , include young children , those with underlying cardiopulmonary disease or immunosuppression regardless of age , and women in the second or third trimester of pregnancy .
Those 65 or older have the highest rates of influenza-associated hospitalisation and mortality ( see figure 7 ). While the 2023 season was considered of low overall clinical severity , this graph reflects the higher risk of influenza-associated death with increasing age . Box 1 lists those at risk of poor outcomes , such as complications , severe influenza , hospitalisation and death .
16 , 29
Adults with uncomplicated influenza typically have fever and systemic symptoms for about three days , following which most show signs of improvement . Respiratory symptoms , in particular recurrent cough , may persist beyond the 2-5 days of systemic symptoms . Complete recovery may take up to two weeks and can be even longer in older adults . 7 , 16
A subset of people have symptoms of weakness or fatigue lasting several weeks , with a post-infectious delay in return to normal levels of activity . Pulmonary function is reduced after acute influenza and even in those with a regular exercise routine , such as runners , a decline in prior level of performance may last for a month or more . In the elderly , though the respiratory presentation may be less marked , there is often a temporary decline in baseline activity and a loss of appetite . 7 , 16
Figure 3 . Laboratory-confirmed influenza notifications , 2006 to 2010 , Australia , by month and year of diagnosis . Annual report of the National Influenza Surveillance Scheme , 2010 13 NNDSS = National Notifiable Diseases Surveillance System .
Figure 4 . Symptoms of influenza .
COMPLICATIONS
COMPLICATIONS vary by age , immune function , and underlying medical conditions . Influenza infection may lead to exacerbations of underlying chronic disease , such as COPD or heart failure . 29
The most common complication of influenza is pneumonia , which includes primary influenza pneumonia , mixed bacterial and viral pneumonia and secondary bacterial pneumonia . In healthy young individuals , bacterial pneumonia complicates about 0.5 % of cases , while it occurs in at least 2.5 % of older individuals and those with predisposing conditions . 31 Bacterial pneumonia
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Figure 5 . Viral pharyngitis .
Department of Health and Aged Care typically occurs within a few days of the onset of influenza ; consider pneumonia in those with persistent symptoms and signs ( including high fever and dyspnoea ) after 3-5 days of acute influenza , in those with a recrudescence of symptoms or those who demonstrate progressive symptoms . 31 Pneumonia can occur with or without pleural effusion and can progress rapidly to respiratory failure , acute respiratory distress syndrome , and refractory hypoxaemia . 16
Streptococcus pneumoniae is the most common cause of secondary bacterial pneumonia . Other bacterial pathogens that can complicate influenza include Staphylococcus aureus ( both methicillin susceptible and methicillin resistant ) and Streptococcus pyogenes . Less common co-infecting bacteria include Pseudomonas aeruginosa , Haemophilus influenzae , Klebsiella pneumoniae , Moraxella catarrhalis , and Escherichia coli . 32 In those severely unwell with respiratory failure requiring ICU admission , influenza may be complicated by invasive aspergillosis , even in those with no or milder immunosuppression . 33 Other potential complications include otitis media , bronchiolitis and croup in young children and sinusitis in older children and adults , while bronchospasm and bronchitis can occur at any age . 16
Extrapulmonary complications
The most common extrapulmonary manifestation of influenza is myositis , more commonly seen in influenza B infection and children . It is characterised by severe muscle pain , muscle tenderness most frequently of the lower extremities , elevated creatine kinase levels and myoglobinuria that
16 , 34 can lead to renal failure .
Critically ill patients may present with multiorgan failure ( respiratory and renal ), shock and sepsis . 23 While elevation of hepatic aminotransferases can be common , liver failure is rare . 36
Cardiac complications include MI , heart failure , and rarely , myocarditis and pericarditis . There is a consistent epidemiological link between influenza epidemics and excess cardiovascular hospitalisations with a cross-sectional study of more than 80,000 adults with laboratory-confirmed influenza demonstrating 11.7 % had an acute cardiovascular event , the most common events were acute heart failure and acute ischaemic
16 , 35 heart disease .
While neurological involvement is infrequent , influenza has been associated with a broad range of neurological complications including seizures , encephalopathy , encephalitis , stroke , acute disseminated encephalomyelitis , transverse myelitis and Guillain-Barre syndrome ( GBS ). Neurological manifestations occur more frequently in children than adults , who most commonly present with febrile seizures , increased seizure frequency in those with seizure disorders , or self-limited encephalopathy . Reye ’ s syndrome , a rapidly progressive disease characterised by encephalopathy and fatty infiltration of the liver , has , since the recognition of the role of aspirin as an important cofactor , seen a marked reduction in incidence because of the avoidance of aspirin in the treatment of viral infections . 23 , 36 An association between bacterial meningitis caused by Neisseria meningitidis and influenza has been reported . 23
Influenza during pregnancy has both maternal and fetal effects ; pregnant patients are more likely to have a more severe clinical course , be hospitalised and admitted to an ICU , and to die compared with the general population . 23 PAGE 30