Medical Health Encyclopedia

In general, the flu is usually self-limited and not serious. About 1% of people who contract the flu end up in the hospital. An estimated 36,000 people currently die each year of influenza-related complications. The highest risks for serious complications occur in people over 65 years old and in those with other medical conditions. Influenza A is the most severe strain and causes an estimated average of 142,000 hospitalizations per year. Influenzas B tends to be milder.

Pneumonia. Pneumonia is the major serious complication of influenza and can be very serious. It can develop about 5 days after viral influenza. Older adults account for more than 90% of the deaths caused by influenza and pneumonia. The growing elderly population will most likely cause an increase in deaths from influenza. Nursing homes patients are especially hard-hit by flu epidemics, with fatality rates as high as 30%.  Flu-related pneumonia nearly always occurs in high-risk individuals such as the following:

• People with weakened immune systems, such as AIDS patients.
• Very young children -- may be difficult to tell whether pneumonia is related to influenza or caused by respiratory syncytial virus (RSV)
• Hospitalized patients and anyone with serious medication conditions, such as diabetes or heart, circulation, or lung disorders, particularly chronic lung disease
• Drug abusers who use needles

Combinations of these factors further increase the risk. It should be noted that pneumonia is an uncommon outcome of influenza in healthy adults.

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Complications in the Central Nervous System in Children. Influenza increases the risk for complications in the central nervous system of small children. In a 2001 Chinese study, children hospitalized with influenza A had a higher risk for fever related seizures than children with other upper respiratory tract infections. In rare cases, influenza can lead to meningitis and encephalitis (inflammations in the central nervous system). The risks decline after a child turns 1 year old, but are still high in children aged 3 to 5 years old.

Pandemics