In general, influenza is spread through respiratory particles or droplets. When a person with flu sneezes or coughs, thousands of droplets, usually invisible, are sent into the air like a cloud. Whomever comes in contact with the particles can get infected. Furthermore, if a person with flu sneezes into his hand or wipes his nose or face, when he touches the doorknob or other object, he leaves thousands of infectious particles. The next person comes along and opens that door, and takes flu virus onto her hand. When she touches her nose, she takes in the virus where it can infect her.
If the immune system is up to the task, the virus particles are identified and destroyed by an incredibly complex process. If the virus gets past the immune response, it infects cells in the delicate mucous membrane tissues in the nose, throat, mouth, and eyes. Infection is when the virus gets past the immune response, sticks to the cells, and then gets inside the cells.
Once inside the cell, the virus hijacks the cell's machinery and instructs it to make more viral proteins and genes. When the virus has reproduced all of its proteins, new viruses come out of the cell, typically killing the cell when they leave. The process is very efficient. In most cases, a virus that infects a cell can multiply into 2,000 or 3,000 new ones. When the newly infected person coughs or sneezes, they are blown out where they can infect the next person.
This process of infection and transmission is what motivates the most important responses and actions to a flu pandemic—prevention of transmission. This site has resources and information to help you understand how to prevent spreading the flu. The main ideas are that someone who is sick should stay home from work or school for at least 7 days or until 24 hours after symptoms clear. They should clean their hands regularly with soap and water or alcohol based sanitizer. They should wear an N95 facemask if they are going to be around other people. It is everyone’s responsibility to reduce the likelihood of transmission, especially people who are sick with flu. Read "If you get sick..." for more details.
While the medical training the most doctors and I went through focuses on “the germ”, science is beginning to confirm our common sense that “the soil” is also important. That means that having a healthy mind, body, and immune system are also key factors in reducing flu infections. And in a pandemic, it may be that enhancing resistance to infection is as important as focusing on killing germs. As I discuss in “how dangerous is the swine flu”, a flu pandemic can last more than a year. We can’t exactly wear respirators around and all stay indoors for that long. So we need to also use this pandemic as an opportunity to adopt healthier lifestyles and behaviors. See Boost your Immunity for information and suggestions on reducing susceptibility to infections.
Some Questions and Answers from the Centers for Disease Control:
How long can an infected person spread this virus to others?
At the current time, CDC believes that this virus has the same properties in terms of spread as seasonal flu viruses. With seasonal flu, studies have shown that people may be contagious from one day before they develop symptoms to up to 7 days after they get sick. Children, especially younger children, might potentially be contagious for longer periods. CDC is studying the virus and its capabilities to try to learn more and will provide more information as it becomes available.
Can I get infected with this new H1N1 virus from eating or preparing pork?
No. H1N1 viruses are not spread by food. You cannot get this new HIN1 virus from eating pork or pork products. Eating properly handled and cooked pork products is safe.
Is there a risk from drinking water?
Tap water that has been treated by conventional disinfection processes does not likely pose a risk for transmission of influenza viruses. Current drinking water treatment regulations provide a high degree of protection from viruses. No research has been completed on the susceptibility of the novel H1N1 flu virus to conventional drinking water treatment processes. However, recent studies have demonstrated that free chlorine levels typically used in drinking water treatment are adequate to inactivate highly pathogenic H5N1 avian influenza. It is likely that other influenza viruses such as novel H1N1 would also be similarly inactivated by chlorination. To date, there have been no documented human cases vof influenza caused by exposure to influenza-contaminated drinking water.
Can the novel H1N1 flu virus be spread through water in swimming pools, spas, water parks, interactive fountains, and other treated recreational water venues?
Recreational water that has been treated at CDC recommended disinfectant levels (1–3 parts per million [ppm or mg/L] for pools and 2–5 ppm for spas) does not likely pose a risk for transmission of influenza viruses. Currently, there are no documented human cases of influenza caused by exposure to influenza-contaminated swimming pool water. No research has been completed on the susceptibility of the novel H1N1 flu virus to chlorine and other disinfectants used in swimming pools, spas, water parks, interactive fountains, and other treated recreational venues. However, recent studies have demonstrated that free chlorine levels recommended by CDC are adequate to disinfect highly pathogenic H5N1 avian influenza virus. It is likely that other influenza viruses such as the novel H1N1 flu virus would also be disinfected by these chlorine levels.
Can H1N1 influenza virus be spread at recreational water venues outside of the water?
Yes, recreational water venues are no different than any other group setting. The spread of this novel H1N1 flu is thought to be happening in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing of people with influenza. Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose.