Viral Infection
Swine flu (H1N1 influenza) is the result of a mutated influenza virus. As Medline notes, influenza is common among animals such as swine. These viruses can mutate, which allows them to infect humans as well. When humans are infected with H1N1, the virus typically enters the body through the respiratory system. The H1N1 virus penetrates cells in the respiratory system and uses the internal machinery of the cells to make additional copies of the virus. Once the virus has made many copies of itself within the cell, it escapes (typically by breaking the cell apart) and can then spread to other tissues.
Transmission
According to the Centers for Disease Control and Prevention, the H1N1 flu is thought to spread from human to human in a way that's very similar to other forms of the flu (such as seasonal influenza). This means an infected person can transmit the virus to other people mainly via coughing or sneezing. When this occurs, droplets of fluid from the respiratory system are expelled into the air, where they can be inhaled by people nearby. The virus can also be transmitted if an infected person coughs or sneezes and then touches an object (such as a doorknob) and then uninfected people touch the contaminated surface. Most experts also say that kissing and even hugging should be avoided. Medline notes that swine flu cannot be caught by eating pork that has been cooked.
Transmission Window
There is a specific period during which people with H1N1 infections are infectious, meaning they can pass the virus to other people. This transmission window begins the day before a patient develops swine flu symptoms and typically extends five to seven days after symptoms occur. This means people who have been infected with swine flu can pass the virus to people before they know they're sick. People with weakened immune systems (including people over age 65) may have a longer period during which they are infectious.
