Colds and the Flu - Complications

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• People with weakened immune systems, such as AIDS patients
• Very young children -- [it may be difficult to tell whether pneumonia is related to influenza or caused by respiratory syncytial virus (RSV)]
• Hospitalized patients and anyone with serious medical conditions, such as diabetes, 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.

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

Every year, influenza strikes millions of people worldwide. Influenza epidemics are most serious when they involve a new strain against which most people are not immune. Such global epidemics (“pandemics”) can rapidly infect more than one fourth of the world's population. For example, the Spanish flu in 1918 and 1919 killed an estimated 20 million people in the U.S. and Europe and 17 million in India. With modern society’s dependence on airline travel, an influenza pandemic could potentially inflict catastrophic damage on human lives and disrupt the global economy.

The influenza virus mutates rapidly as it moves from species to species. Most Type A influenza strains first develop in migratory waterfowl populations. While most avian influenza (“bird flu”) virus strains are relatively harmless, a few subtypes develop into “highly pathogenic avian influenza” that can be deadly for domesticated poultry and livestock -- and, as recent events have shown, even humans. The medical community is now greatly concerned about the H5N1 bird flu virus, which has infected many people in several countries, and has lead to death. People can become infected from contact with contaminated chickens and pigs. Scientists’ greatest fear is the emergence of a highly contagious virus that spreads from person to person and causes severe illness or death.

Review Date: 03/06/2007
Reviewed By: A.D.A.M. Editorial Team: Greg Juhn, M.T.P.W., David R. Eltz, Kelli A. Stacy. Previously reviewed by Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital (12/4/2006).