Medical Health Encyclopedia

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.

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Certain genetic disorders predispose people with these problems to respiratory infections. They include sickle-cell disease, cystic fibrosis (which causes mucus abnormalities), and Kartagener's 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 six-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 exacerbate symptoms.

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