What are colds and flu's?

Answer 1

They are upper respiratory infections caused by viruses. Viruses are non-living organisms that use the lytic and lysogenic cycles to reproduce. See the related question below for more information about the lytic cycle which is the process of viral replication.

Answer 2

Colds and flus are infections caused by viruses.

The "Common Cold" has symptoms in the upper respiratory tract like sneezing, scratchy throat, and runny nose, but adults don't typically have fevers. Colds are usually caused by the rhinovirus (up to 40% of colds), or Coronaviruses (about 20%), but there are more than 200 viruses that can cause the common cold.

The flu is caused mostly by Type A and Type B Influenza viruses. Flu starts with similar symptoms as a cold only it hits faster and harder and usually includes fever in adults.

Although the "stomach flu" is a common term, it is not a real diagnosis. The proper medical term for stomach flu is gastroenteritis (an intestinal disease, sometimes viral but also bacterial), it is often mistaken for influenza because the flu can sometimes include vomiting and diarrhea. Stomach flu is often caused by the norovirus, nicknamed the Norwalk Flu but there are many other viruses that can cause the same GI symptoms.

These types of viral infections are usually short term illnesses that are over in 10 - 14 days in most otherwise healthy people. If symptoms continue beyond two weeks, then you should contact your health care professional to be sure that you do not have a different type of illness or to be sure you do not have a secondary complication such as pneumonia.