Nicole Martin age 13, of Decatur, Ill., for her question:

HOW DOES INFECTION ENTER THE BODY?

Infection is the injurious contamination of the body or part of the body by pathogenic agents, such as fungi, bacteria, protozoa or viruses, or by the toxins that these agents may produce.

Infectious agents may enter the body of the host by several routes. The most common route is through the respiratory passages and gastrointestinal tracts, but other common entry routes are through the skin, especially injured skin, the mucosal surfaces of other body openings and the conjunctiva of the eyes.

Resistance to infection is lowered by many diseases of the immune system, cancer and leukemia as well as by conditions such a severe burns or malnutrition.

In healthy persons, the body's own so called natural flora of bacteria form a line of defense against mild infections, which may thus be taken care of without further treatment.

Antibiotic and sulfa drugs and other pharmaceuticals are prescribed by doctors and used against more severe infections, and vaccines serve as preventive measures against a wide range of infectious diseases.