Common Immune System Attackers
According to Harvard Medical School's Consumer Health Information, more than 200 viruses that can cause the common cold have been identified. The biggest offender, the rhinovirus, causes up to 40 percent of colds—and the common cold causes nearly 26 million days of missed school and 23 million days of absence from work every year in the United States.
Upper respiratory infections, otherwise known as colds, are passed through direct contact with an infected person or through the air from sneezes or coughs. Children are especially vulnerable to communicable diseases because they tend to touch their mouths, noses and eyes without thinking, then handle toys or come in direct contact with another child. They may also forget to cover their mouths when coughing and sneezing, neglect washing hands, and innocently ignore their running noses.
When a person contracts a cold, symptoms are evident one to three days later. Infants with colds may experience an inability to sleep, fussiness, congestion, and sometimes diarrhea and vomiting. In addition to these symptoms, older children and adults may also have a scratchy throat, watery eyes, sneezing, a mild hacking cough, muscle aches, and fatigue. Symptoms differ in adults and children, and vary from person to person, but they normally last about a week.
Influenza, or the flu, is caused by a virus and is usually transmitted through the air. The flu can be spread one day prior to exhibiting symptoms—making the cause trickier to identify. Adults can transmit the flu three to seven days after symptoms begin, and children can transmit it for more than seven days.
Unlike the common cold, the flu can lead to pneumonia and, in most severe cases, death. There are many different strains of flu, and the viral infection generally starts with symptoms such as fever, cough, nasal discharge, headache, muscle aches, chills, fatigue, sore throat, nausea, and loss of appetite.
The Centers for Disease Control (CDC) warns, "Millions of people in the United States—about five percent to 20 percent of US residents—will get influenza each year. An average of about 36,000 people per year in the United States dies from influenza, and more than 200,000 have to be admitted to the hospital as a result of influenza."