Table 2.

Complications associated with influenza

	Complications	Considerations
Upper-respiratory complications	Otitis media, parotitis, sinusitis, and laryngotracheobronchitis	Otitis media, parotitis, and laryngotracheobronchitis are more common in children than adults
Lower-respiratory complications	Bronchiolitis, bronchitis, reactive airway disease, pneumonia, respiratory failure, and acute respiratory distress syndrome	Bronchiolitis is more common in young children than in adults
Cardiac complications	Myocardial infarction, myocarditis, pericarditis, and heart failure	Influenza might precipitate myocardial infarction or heart failure in people with coronary artery disease; cardiac complications can result in critical illness with fatal outcomes
Gastrointestinal complications	Hepatitis, pancreatitis, and severe acute abdomen-like pain	Hepatic failure is rare
Musculoskeletal complications	Myositis, rhabdomyolysis, and compartment syndrome	Severe myositis (soleus and gastrocnemius) can occur in school-age children; myoglobinuria can cause acute kidney injury
Renal complications	Acute kidney injury and kidney failure	Can occur with severe pneumonia
Neurological complications	Encephalopathy, encephalitis, meningoencephalitis, febrile seizures, cerebrovascular accident, transverse myelitis, acute demyelinating encephalomyelitis, Reye syndrome with salicylate exposure, and Guillain-Barré syndrome	Encephalopathy and encephalitis are more common in young children, can be acute or postinfectious with full neurological recovery, sequelae, or fatal outcomes; Reye syndrome is rare in children without salicylate exposure, and Guillain Barre syndrome is uncommon
Co-infections	Pneumonia, ventilator-associated pneumonia, tracheitis, and meningitis	Invasive bacterial, viral, and fungal coinfections can cause critical illness and fatal outcomes
Other complications	Exacerbation of chronic disease, dehydration, sepsis, toxic shock syndrome, sepsis-like syndrome or sudden death in young infants, premature labour, and fetal loss in pregnant people	People of all ages with chronic disease can experience worsening of underlying conditions (eg, chronic obstructive pulmonary disease exacerbation in adults, acute chest syndrome with sickle cell disease, worsening of asthma, and heart failure)

Adapted from Uyeki and colleagues.²⁶