Both influenza and the common cold are viral respiratory infections (they affect the nose, throat, and lungs). These viruses are spread from person to person through droplets that are sneezed out or coughed up by an infected person. In some cases, the viruses can be spread when a person touches an infected surface (e.g., doorknobs, countertops, telephones) and then touches his or her nose, mouth, or eyes. As such, these illnesses are most easily spread in crowded conditions such as schools.
Influenza is commonly referred to as "the flu." Each year, millions of Canadians come down with influenza. Although most people recover fully, it results in about 12,000 hospitalizations and 3,500 deaths in Canada annually. Deaths due to the flu are found mostly among high-risk populations, such as those with other medical conditions (such as diabetes or cancer) or weakened immune systems, seniors, or very young children. There are 3 types of influenza viruses: A, B, and C. Type A influenza causes the most serious problems in humans.
There are over 200 different known cold viruses, but most colds (30% to 40%) are caused by rhinoviruses. In Canada, the peak times for colds are at the start of school in the fall, in mid-winter, and again in early spring. Adults catch approximately 2 to 4 colds a year, and children catch even more.
People infected with an influenza or cold virus become contagious 1 to 2 days before symptoms develop. Adults remain infectious (can spread the virus to others) for about 6 days, and children remain infectious for up to 10 days.