Risk Factors

Colds and flus are spread primarily when an infected person coughs or sneezes near someone else. Everyone gets a cold or upper respiratory infection at some time:

On average, every American has two to four colds a year.
Each year, there are 18 - 20 million cases of respiratory infections caused by influenza.

Age

The very young and the very old are at higher risk for upper respiratory tract infections and for complications from them.

Children. Young children are prone to colds and may have eight to 12 colds every year. Millions of cases of influenza develop in American children and adolescents each year.

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Before the immune system matures, all infants are susceptible to infections, with a possible frequency of one cold every 1 - 2 months. Smaller nasal and sinus passages also make children more vulnerable than older children and adults. Infections gradually diminish as they grow, until at school age their rate is about the same as an adult's. There is almost never cause for concern when a child has frequent colds unless they become unusually severe or more frequent than usual.

The Elderly. The elderly have diminished cough and gag reflexes and faltering immune systems and are at greater risk for serious respiratory infections than are young and middle-aged adults.

Exposure to Smoke and Environmental Pollutants

The risk of respiratory infections is increased by exposure to cigarette smoke, which can injure airways and damage the cilia (tiny hair-like structures that help keep the airways clear). Toxic fumes, industrial smoke, and other air pollutants are also risk factors. Parental smoking increases the risk of respiratory infections in their children.

Medical Conditions

People with AIDS and other medical conditions that damage the immune system are extremely susceptible to serious infections.

Cancers, especially leukemia and Hodgkin's disease, put patients at risk. Patients who are on corticosteroid (steroid) treatments, chemotherapy, or other medications that suppress the immune system are also prone to infection.