As U.S. officials warn of the spread in swine flu cases across the country, there are a number of steps Americans can take to protect themselves and their children from this unique virus.
The rapidly spreading swine flu is a new virus that includes combination of swine, bird and human strains. It has taken the lives of 81 people in Mexico, and sickened more than a thousand south of the border.
In the United States, 20 cases have been confirmed thus far -- seven in California, two in Kansas, eight in New York City, one in Ohio and two in Texas.
Simple preventive measures, such as washing hands frequently and avoiding people who are coughing or sneezing, can go a long way toward keeping Americans safe from the virus, which health officials expect is likely to afflict more people.
"There is a role for everyone to play when an outbreak is going on to try and reduce the impact," said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention (CDC). "At an individual level, it's important people understand how they can prevent respiratory infection. Frequent handwashing [is an] effective way to reduce transmission of diseases."
The World Health Organization declared the unusual virus a "public health emergency of international concern," but fell short of calling it a pandemic.
A flu virus can reach pandemic status if three conditions are met, according to the World Health Organization.
First, it must be an infection that has newly emerged. Secondly, it has to be able to cause serious illness in humans. And thirdly, it must be able to spread easily from person to person. Infections in this category can often spread beyond their continents of origin -- and potentially around the world.
When a flu virus mutates in such a way that it forms a novel version, it means people typically have little to no protection, because their immune systems have no experience fighting that form of the virus. Flu viruses can spread quickly and potentially cause more severe illness when the population lacks immunity.
Scientists around the globe are working hard to determine the threat level of the current swine virus. Right now, the virus is said to have "pandemic potential" because it is a new virus that can spread from person-to-person.
But if it turns out the virus does not spread easily among people, the threat level will go down. Similarly, if it turns out the virus can spread easily among people, the threat becomes more serious and the virus is more likely to trigger a pandemic.
"The distinction about a pandemic is that you need a distinct virus that human population hasn't seen before. Once it starts to spread, it moves rapidly from country to country and from continent to continent and we don't have that yet," said Dr. William Schaffner, chairman of Preventive Medicine at Vanderbilt University Medical Center in Nashville, Tenn.
He added that it is still too early to use the "P" word just yet.
"I'm still observing this as a variant of seasonal influenza. I don't know if we've seen that kind of [global] spread yet so I'm a little bit cautious. However it's in everyone's mind," he said.
But all pandemics are not equally deadly. Some kill millions more people than normal flu outbreaks, while others are roughly on par with seasonal flu in terms of deaths.
It is not possible to predict a pandemic in advance, so health officials keep a close watch on viruses that have "pandemic potential" -- new viruses that have shown at least some ability to transmit to humans.
The current H5N1 bird flu circulating in Asia is an example of a virus that has pandemic potential, but has not yet caused a pandemic.
Pandemics can vary quite a bit in severity. The 1918 pandemic killed many more Americans than an ordinary flu, while the 1968 version killed about 34,000 people -- about the same number killed each year by seasonal flu, according to CDC statistics.
The world generally experiences at least two flu pandemics each century.
Declaring a public health emergency allows states to free up their resources for prevention of the disease in question.
That declaration gives the head of the Department of Health and Human Services authority to take rapid measures -- including authorizing contacts and mobilizing the national disaster system -- to respond to the disease, including allowing the use of unapproved drugs.
Scientists have not yet determined the reason why there are reported swine flu deaths in Mexico while cases in the United States have thus far been mild.
The WHO noted that the U.S. cases have all been confirmed by laboratory analysis, while those in Mexico have not all been confirmed as yet. This means that health officials do not know how many people who died in Mexico perished because of the new swine flu virus.
However, the CDC is concerned that because the virus is genetically similar in the United States and Mexico, the United States will see more severe illness as new cases emerge, including some deaths.
What many people do not realize is that the flu is generally a much more serious illness than most people appreciate. Even the "typical" flu season results in 36,000 American deaths each year, according to CDC statistics.
The swine flu is a type of influenza virus usually found in pigs. The most common version is H1N1, and the current virus causing concern is a new variation of that virus. Swine flu does not typically pass to humans directly, but such transmission can occur. The current swine flu virus concerns health experts because it has shown the ability to pass from human to human.
When a person gets the swine flu virus, it takes 48 hours before the infected person actually begins to feel ill.
"It takes time for the virus to get down and start to create an illness. That interval between exposure and onset of illness is called the incubation period. The virus hasn't manigested itself," Schaffner said.
Once a person becomes ill, they can stay that way for anywhere from 48 hours to seven days. So far, in the United States, the cases of swine flu have been mild.
There is no vaccination for the swine flu system. U.S. and WHO officials said they are beginning work on a vaccine, but that could take months to develop.
Two prescription anti-viral drugs -- Tamiflu and Relenza -- have proved effective in combating the swine flu virus in victims in the United States. The Obama administration has released 12.5 million courses of the country's stockpile of 50 million courses of Tamiflu.
Health officials and doctors don't recommend people go to the hospital if they are experiencing flu-like symptoms. Rather, they should contact their doctor.
Doctors recommend getting rest and drinking plenty of fluids, and using Tylenol and Advil, which have proven effective for flu symptoms.
Doctors recommend "self-quarantine" for those inflicted with the influenza, so that it does not spread to others. If children are sick, they should not be sent to school. For adults, they should stay away from their workplaces and maintain as much distance as possible from others. Travel on buses or airplanes is not recommended.
Doctors say it is only natural for flus to spread in places like schools, where there is a lot of interaction.
It is hard to distinguish the symptoms of a swine flu from any other flu.
Schaffner said the one distinction is that the swine flu is not a common cold.
"Common cold has its symtoms from the neck up -- sore throat, stuffy nose and feeling crummy. However influenza tends to make you feel much more ill. You can have a sore throat but then you also get cough and muscle aches and pains," he said.
Hayden Henshaw, an 18year-old from Cibolo, Texas, who was diagnosed with the swine flu last week, said he felt regular flu symptoms.
"You just get really run down, my skin and my muscles were achy. I had a cough and slightly feverish." he told ABC News.
His father, Patrick and 11-year-old sister, Hannah, also got the flu from him.
"It's just like any other flu but the vaccine doesn't help with this strain," his mother, Robin, told ABC News.
Doctors recommend looking out for symptoms such as a fever of more than 100 degrees, body aches, coughing, a sore throat, respiratory congestion and, in some cases, vomiting and diarrhea.
In the absence of symptoms, officials say people don't have to get tested. If they are experiecing the symptoms, they you should take precaution and stay away from others.
The WHO is developing a profile of the "typical case" of swine flu, but thus far, the symptoms appear to be essentially the same as those for the usual winter flu. The only way to definitively diagnose swine flu is to have laboratory testing done to determine the exact subtype of the virus.
The WHO has a six-phase approach for dealing with large outbreaks of viruses. The six threat levels help the organization determine the course of action it needs to take and the kind of guidelines and recommendations it needs to provide to countries.
Phase 1 means no viruses circulating among animals are reported to have caused infections in humans. The Phase 2 threat is activated when the virus has spread from animals to humans and has "potential pandemic threat."
The threat level is escalated to Phase 3 -- such as after the swine flu spread -- when the virus is reported in clusters, but has not resulted in enough human-to-human transmission to have caused a large outbreak at the community level.
Phase 4 means the virus has resulted in "community-level" outbreaks, and is at a strong risk of becoming a pandemic.
Phases 5 and 6 mean there is widespread human infection, and the uptick to Phase 5 means that a global pandemic is on its way. Phase 6 is post-peak, meaning the virus has dropped from its most sever but hasn't completely disappeared.
In the post-pandemic period, influenza disease activity will have returned to levels normally seen for seasonal influenza.
Currently, the WHO has a threat level of 3 but is considering raising it to 4. WHO officials said they are not yet convinced that this is a pandemic and there are still a lot of questions about the strength and lethality of the swine flu virus.
"[Prevention is] no different than any other pandemic flu, and those are kind of simple things -- wash your hands a lot, don't shake hands or hug or kiss people if you're sick, don't go to work, self-qurantine yourself," said Peter Katona, an associate professor at the University of California, Los Angeles (UCLA) Medical Center.
1. Wash hands frequently: This will lessen the chance of carrying or transmitting any viruses that normally get stuck on the hands in day-to-day activities. Try to avoid rubbing eyes or touching nose with dirty hands. Wash hands often with soap and water, especially after coughing or sneezing. Alcohol-based hand cleaners are also effective.
2. Try to avoid people who are coughing and sneezing: The CDC advises people to cover their nose and mouth with a tissue when they cough or sneeze and throw the tissue in the trash after using it. Try to teach your kids to do the same. Influenza is thought to spread mainly person-to-person through coughing or sneezing of infected people.
3. If experiencing flu-like symptoms, don't go out -- stay at home. Call a healthcare provider, particularly if a person has been to Mexico, southern California and southern Texas. The CDC recommends that people who get sick stay home from work or school and limit contact with others to keep from infecting them.
4. Taking a trip to Mexico? Rethink your plans. Schaffner said that unless you have a compelling reason to go, you might want to reconsider. Many airlines, including Continental, US Airways and American Airlines, are waiving cancellation fees on tickets to Mexico.
5. Stay informed and plan ahead: Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, said it's important to stay informed about what's going on in one's community, and whether the authorities -- such as the state or county health departments -- have issued any recommendations. It's a good idea to plan for what to do if children's school is closed.
6. Keep sick kids out of school, and stay home from work if you are sick. Aside from providing needed rest, such absences protect others from catching whatever you or your kid has. Keep at least a few feet's distance if you have the flu or are interacting with someone who has the flu. The communicable distance for most flu viruses is about three feet, so keep clear of this radius in order to avoid spread. If dealing with a flu case at home, make sure the flu sufferer (and even those who interact with this person) wear facial masks to lower the chances of spread.
7. Avoid surfaces and objects that may be handled by many people. For kids, this may include doctor's office toys, surfaces that a lot of other kids are touching. Keep all surfaces and objects around the house clean. This becomes especially relevant if there is someone in that house who is sick or has the flu already. Try to teach kids not to touch their faces. This is like mass transit for germs: straight from the hands to the eyes, nose and mouth.
The CDC advises those who feel symptoms to contact their doctor right away. And finally, one myth that can be dispelled: There are no signs that people can get the swine flu from eating pork.
Here are some useful Web sites for more information:
ABC News' Dan Childs, Desiree Adib, John Hendren and Joanna Schaffhausen contributed to this report.