Both influenza and the common cold are viral respiratory infections (they affect the nose, throat, and lungs). Viruses are spread from person to person through airborne 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, 10% to 20% of Canadians are stricken with influenza. Although most people recover fully, depending on the severity of the flu season, it can result in an average of 20,000 hospitalizations and approximately 4000 to 8000 deaths annually in Canada. 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. Children catch approximately 8 colds per year, adults catch roughly 4 per year, and seniors about 2 per year.
Many people confuse the flu with a bad cold. The following table highlights the differences between influenza and the common cold:
| Symptom | Flu | Cold |
| Fever | Usually present, high (102°F to 104°F or 38°C to 41°C); lasts 3 to 4 days | Uncommon |
| Headache | Very common (can be severe) | Uncommon |
| Aches and pains | Common and often severe | Slight |
| Fatigue and weakness | Starts early, can be severe, and can last up to 14 to 21 days | Mild |
| Extreme exhaustion | Very common at the start | Never |
| Stuffy nose | Sometimes | Common |
| Sneezing | Sometimes | Common |
| Sore throat | Sometimes | Common |
| Chest discomfort, cough | Common | Mild to moderate, hacking cough |
| Complications | Can lead to pneumonia or respiratory failure; can worsen a current chronic condition; can be life-threatening | Can lead to sinus congestion or earache |
People infected with an influenza or cold virus become contagious 24 hours after the virus enters the body (often before symptoms appear). Adults remain infectious (can spread the virus to others) for about 6 days, and children remain infectious for up to 10 days.
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