Colds and the flu
Description
An in-depth report on the diagnosis, treatment, and prevention of colds and flu.
Alternative Names
Influenza; Strep throat; Bird flu; Avian influenza
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:
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On average, every American has two to four colds a year.
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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.
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.
People with diabetes are at higher risk for flu.
Certain genetic disorders predispose people with these problems to respiratory infections. They include sickle-cell disease, cystic fibrosis (which causes mucus abnormalities), and Kartagener syndrome (which results in malfunctioning cilia).
People under Stress
Much evidence suggests that stress increases one's susceptibility to a cold. In one study, people with high stress levels averaged 2.7 upper respiratory infections during a 6-month period and those reporting low stress averaged 1.5 infections. Stress appears to increase the risk for a cold regardless of lifestyle or other health habits. And once a person catches a cold or flu, stress can make symptoms worse.
It is not clear why these events occur. Some experts believe that stress alters specific immune factors, which cause inflammation in the airways. One 2001 study reported that the only people who got sick after experiencing short stress were those whose body responded to stress with high levels of cortisol, a stress hormone, coupled with a low immune response.
Excessive Exercise
In people who already have colds, exercise has no effect on the illness' severity or duration of the infection. High-intensity or endurance exercises, however, appear to suppress the immune system while they are being performed. Some highly trained athletes, for instance, report being susceptible to colds after strenuous events. People should avoid strenuous physical activity when they have high fevers or widespread viral illnesses. Note: Very low fat diets appear to worsen this dampening effect on the immune system. A higher fat-diet may help redress this imbalance (omega-3 fatty acids, found in fish and canola oil are preferred). Whether carbohydrate loading provides much additional value is not clear.
Seasonal Incidence
Colds and flus occur predominantly in the winter. Flu season typically starts in October and lasts into mid March. In 1999, for example, doctors' office visits significantly increased beginning in December and influenza activity peaked during the first 2 weeks in February.
The reasons for this seasonal bias are not due to the cold itself, but to other factors. Certainly, flus and colds are more like to be transmitted in winter because people spend more time indoors and are exposed to higher concentrations of airborne viruses. Dry winter weather also dries up nasal passages, making them more susceptible to viruses. Some experts theorize that the high rates of viral infections in winter may be due to certain immune factors, which react to light and dark and affect a person's susceptibility to viruses.
Traveling in Trains, Buses, and Planes
Traveling in close contact with people, whether on trains, planes, or buses, can increase the risk for respiratory infections. (A 2002 study suggested that the risk for a cold was about 20% after flying.) There has been particular concern that aircraft air that is recirculated can increase the risk for such infections. The same 2002 study, however, reported no difference in colds and flus among those who traveled in planes with fresh air versus recirculated air.
Day Care Centers
Children who attend day care may have an increased risk of colds. However, a 2002 study suggested that although children in day care centers incur higher rates of the common cold in the preschool years, they have
lower
cold rates in their first years of regular school. The colds they catch in day care, then, may bestow some immunity to future colds for a few years. By age 13, such protection has worn off. There is also some evidence that frequent colds in young children may help protect against future allergies and asthma.
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Review Date: 3/6/2007
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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).
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