Test Your Knowledge

The common cold and flu (influenza) are contagious infections caused by viruses that affect the upper respiratory system. Colds and the flu cause a wide variety of symptoms that are usually mild and resolve without treatment within one to two weeks. Children are particularly vulnerable to catching colds or the flu, and may experience more severe symptoms than adults.

Viruses that cause colds or the flu enter a person’s body through the mouth or nose. This can occur by inhaling airborne particles after someone with the virus has coughed or sneezed. Virus particles can travel up to 12 feet (3.7 meters) through the air with a sneeze or cough. Infection may also occur by touching a contaminated surface (e.g., skin of an infected person, tissue, doorknob, desktop, laptop), then touching one’s own nose or mouth.

Once inside the body, the virus infiltrates the protective lining of the nose and throat. This causes the immune system to attack the invading virus, resulting in irritation and inflammation of the nose and throat. It is actually the immune system’s reaction to a virus that causes the symptoms of a cold or flu (e.g., a sore throat, stuffy or runny nose). In addition, a runny nose, sneezing or coughing actually help eliminate the virus from the body and prevent it from spreading throughout the body. Symptoms of a cold or the flu usually appear anywhere from one to three days after the virus has entered the body.  

A person may develop an immunity or resistance to specific viruses. Antibodies produced by the immune system in response to a particular virus may prevent reinfection by that same virus. However, because there are hundreds of different viruses that can cause infection and most can change their structure (even slightly) so that the body does not recognize the new viral structure, immunity rarely protects a person from catching another cold or flu virus again. Cold and flu viruses can live on surfaces from a few seconds to two days, depending on the surface and the type of virus.

Colds are the most common infectious disease in the United States, according to the American Academy of Family Physicians (AAFP). Americans experience an estimated 1 billion colds per year. In addition, colds are the primary reason children visit the physician and stay home from school.

The flu affects approximately 10 to 20 percent of people in the United States every year, according to the AAFP. About 200,000 Americans are hospitalized every year for the flu, and 36,000 die annually from the flu and its complications, according to the Centers for Disease Control and Prevention (CDC).

Colds and the flu can sometimes lead to more serious conditions. These include:

• Pneumonia. Infection of the lungs that may need to be treated with antibiotics. This is the most common complication of the flu.
  
  
• Ear infections. Infection of the middle (otitis media) or inner ear may occur as a complication of a cold or the flu.
  
  
• Sinusitis. Inflammation of the sinus cavities. This is a frequent complication for children with colds. Sinusitis occurs in 5 to 13 percent of children with colds – compared to 0.5 to 2 percent of adults with colds.
  
  
• Dehydration. Significant loss of fluids in the body. This may occur as a result of severe cold or flu symptoms. It may be life-threatening in infants and small children.
  
  
• Worsening of existing medical conditions. Symptoms of colds or the flu may aggravate any other existing medical conditions, such as congestive heart failure, asthma and diabetes.