The following are the most important diseases or complications that may be contributed to by influenza (flu):
Respiratory system (J00-J99)
- Bronchitis – inflammation of the bronchi.
- Bronchopneumonia, secondary-bacterial (caused by pneumococcus, Staphylococcus aureus, or Haemophilus influenzae).
- Pulmonary edema – accumulation of water in the lungs.
- Pneumonia (pneumonia) – primary hemorrhagic or interstitial pneumonia; primarily viral, possibly with bacterial pulmonary complications, esp. with pneumococcalNote: After a double infection with Streptococcus pneumoniae and influenza viruses (influenza A virus), the disease is always particularly severe, often even lethal.
- Pseudocroup – viral laryngitis.
- Sinusitis (inflammation of the paranasal sinuses)
Cardiovascular system (I00-I99)
- Cardiomyopathy (heart muscle disease) → severe left heart failure (left heart failure).
- Myocardial infarction (heart attack) – in the first seven days of influenza infection, the risk of myocardial infarction increases 6-fold compared to non-infected individuals.
- Myocarditis (inflammation of the heart muscle).
- Pericarditis (inflammation of the pericardium)
Infectious and parasitic diseases (A00-B99).
- Bacterial superinfection – this refers to the grafting of a bacterial infection (e.g., pneumococcal pneumonia/pneumonia) onto a viral infection
- Invasive pulmonary aspergillosis (IPA) – influenza patients treated in an intensive care unit for a severe course; 90-day mortality (death rate) was 51% vs. 28% in influenza patients without IPA, according to the report
Musculoskeletal system and connective tissue (M00-M99).
- Myositis (muscle inflammation)
- Rhabdomyolysis – dissolution of skeletal muscle.
Liver, gallbladder, and bile ducts – Pancreas (pancreas) (K70-K77; K80-K87).
- Sclerosing cholangitis – inflammation of the extrahepatic and intrahepatic (located outside and inside the liver) bile ducts (1 case report)
Ears – mastoid process (H60-H95).
- Otitis media (inflammation of the middle ear)
Psyche – nervous system (F00-F99; G00-G99)
- Encephalitis (inflammation of the brain).
- Guillain-Barré syndrome (GBS; synonyms: Idiopathic polyradiculoneuritis, Landry-Guillain-Barré-Strohl syndrome); two courses: acute inflammatory demyelinating polyneuropathy or chronic inflammatory demyelinating polyneuropathy (disease of the peripheral nervous system); idiopathic polyneuritis (diseases of multiple nerves) of spinal nerve roots and peripheral nerves with ascending paralysis and pain; usually occurs after infections.
- Meningitis (meningitis).
- Meningoencephalitis (combined inflammation of the brain (encephalitis) and meninges (meningitis)).
- Reye syndrome – acute encephalopathy (pathological change of the brain) with concomitant fatty liver hepatitis (fatty liver inflammation) after a passed viral infection in young children; occurs on average one week after the resolution of the previous disease.
Pregnancy, childbirth, and puerperium (O00-O99).
- Preterm birth (< 37 weeks’ gestation) 3.9-fold risk compared with pregnant women without influenza
- Low birth weight (< 2,500 g) 4.6-fold risk compared with pregnant women without influenza
- Low Apgar score (≤ 6, collected five minutes after birth) 8.7-fold risk compared with pregnant women without influenza
Symptoms and abnormal clinical and laboratory findings not elsewhere classified (R00-R99)
- Multi-organ failure (MODS, multi-organ dysfunction syndrome; MOF: multiple organ failure) – simultaneous or sequential failure or severe functional impairment of multiple vital organ systems of the body.
- Febrile convulsions
Further
- Increase in heart attack deaths one to three weeks after infection
Prognostic factors
- Mutations in IFITM3 (for “interferon-induced transmembrane protein 3″), present in about 20% of Chinese and 4% of people of European ancestry, result in increased replication of the virus. This is known to lead to severe courses of influenza pneumonia (swine flu H1N1 2009/10) and, according to a recent study, also to increased cardiac complications.For carriers of the IFITM3 mutations, this means they are likely to be at increased risk for sudden cardiac death (PHT).