Complications associated with influenza infection in adults
| Complication | Incidence | Comments |
|---|---|---|
| Respiratory | ||
| Acute bronchitis | Common | More common in elderly and those with chronic medical conditions |
| Primary viral pneumonia | Uncommon | Onset within 48 hours of start of fever |
| Secondary bacterial pneumonia | Common | Typically occurs four to five days after onset of illness |
| Cardiovascular | ||
| ECG abnormalities | Common | Non-specific T wave and rhythm changes, ST segment deviation. Mostly not associated with cardiac symptoms |
| Myocarditis | Rare | |
| Pericarditis | Rare | |
| Muscle | ||
| Myositis | Uncommon | Occurs during early convalescence |
| Myoglobinuria and renal failure | Rare | |
| Central nervous system | ||
| Encephalitis/encephalopathy | Rare | Occurs within first week of illness. More common in children and in Japan |
| Transverse myelitis | Very rare | |
| Guillain-Barré syndrome | Very rare | |
| Others | ||
| Otitis media | Common | Much more common in children |
| Toxic shock syndrome | Rare | |
| Parotitis | Very rare |