Last updated: Oct 07, 2014
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With all the fearsome sounding flu strains in the news—bird, swine and those letter-number combinations—it's easy to make yourself sick just thinking about them. And it's true: Influenza is a highly contagious, rapidly transforming pathogen that keeps doctors and pharmaceutical companies guessing every year. "Influenza viruses share a similar genetic makeup, and they all infect the respiratory system," says Robert Salata, MD, chief of infectious diseases at University Hospitals Case Medical Center in Cleveland. "But there are several types and subtypes, some of which are more of a threat than others." Here's all you need to know about what could be circulating this winter.



Seasonal flu

Scary stats: Although regular old influenza may not seem as frightening as some of its more exotic siblings, the flu hospitalizes about 200,000 Americans a year and kills anywhere from 3,000 to 49,000 annually in the U.S. "Seasonal flu" actually refers to several circulating strains of influenza, says Lisa Grohskopf, MD, medical officer for the Centers for Disease Control and Prevention (CDC). Thanks to flu trackers, scientists can predict fairly accurately which strains will be most common in the U.S. each year.

What it's like: For most healthy adults, seasonal flu lasts about a week and usually goes away on its own. It tends to be more debilitating than the common cold, with symptoms like head and muscle aches, fever, cough, sore throat and a runny nose. Young children, pregnant women and adults 65 and up—plus those with a compromised immune or respiratory system—are most vulnerable to complications.

How it spreads: Usually through the air; less commonly via contact with a contaminated surface.

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Should you worry? Yes. All Americans are at risk of a bad case of seasonal flu. Defend yourself by following common preventions, like washing your hands or getting the flu vaccine.

H1N1 flu

Scary stats: Formerly known as swine flu, this virus surfaced in 2009 and reached pandemic proportions, infecting approximately 60 million people in the U.S. (and killing an estimated 12,000). It has returned every year since, but a vaccine has helped decrease infection rates, and it's now considered a form of seasonal flu.

What it's like: Symptoms are similar to those of other seasonal flu strains, although unlike other strains, H1N1 has been shown to hit healthy adults under 65 especially hard.

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How it spreads: It's transmitted in the same ways as other seasonal flus.

Should you worry? H1N1 could be prevalent again this year, but if you get your general flu shot, you'll have some good protection: Both the trivalent and quadrivalent versions of the flu vaccine include H1N1.



Avian flu

Scary stats: In January, a Canadian woman who had traveled to China died after contracting H5N1, the same strain of "bird flu" that has infected more than 650 people (and killed nearly 400) in Asia and the Middle East since 2003.

What it's like: When humans contract H5N1, they can develop fever and cough and have difficulty breathing. Up to 60% of those infected have died.

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How it spreads: Both of the most common forms of avian flu spread mainly from infected birds to humans.

Should you worry? Not unless you're traveling in countries with outbreaks (including China, Egypt and Indonesia) and hanging around poultry. You can't catch it from eating cooked chicken or handling meat bought at a supermarket.

Variant flu

Scary stats: When a virus present in pigs makes its way to humans, it's considered a variant virus. In the last three years, more than 300 people in the U.S. have been infected by a new strain, H3N2v, mostly after exposure to pigs at state fairs. A vaccine is being developed.

What it's like: For most people, H3N2v feels like a mild seasonal flu, but complications can occur: In 2012, 16 people were hospitalized, and one older adult with underlying health conditions died. The majority of those infected have been children, not adults, probably because H3N2v is related to human flu viruses from the 1990s, so grown-ups tend to have a built-in immunity.

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How it spreads: Humans can become infected via exposure to a sick pig if, for example, it sneezes and a droplet lands in your nose or mouth.

Should you worry? Probably not. Like bird flu, H3N2v doesn't appear to circulate easily among humans, and you can't catch it from eating properly cooked pork. If you do spend time around pigs, wear gloves, wash your hands afterward and avoid any swine that seem to be obviously, well, under the weather.



More to Worry About?
Though these headline-making viruses and bacterial infections haven't yet taken as many lives as influenza, they are still serious public health threats.

Ebola
As of press time, more than 2,400 people have died in the current Ebola outbreak in West Africa, and the virus reached American soil for the first time in August, when infected health-care workers were flown home and treated. The illness involves vomiting and sometimes internal and external bleeding. Transmission is possible only through shared bodily fluids, so unless you're traveling to affected countries, risk of exposure is low. (If visiting West Africa, check the CDC website for travel advisories.)

Norovirus
This so-called stomach flu (it's not related to influenza) causes vomiting and diarrhea and usually lasts one to three days. You can catch it by eating contaminated food or being exposed to germs from an infected person. It made news after spreading on cruise ships earlier this year. Washing your hands often, disinfecting household surfaces and carefully preparing meals are ways to stay safe.

MERS (Middle East Respiratory Syndrome)
First reported in Saudi Arabia in 2012, this respiratory illness causes fever, cough and shortness of breath and has infected nearly 900 people, with a 30% fatality rate. Research suggests that transmission may be airborne and that camels have helped it spread. But so far, cases in the U.S. have been limited to two people who traveled abroad.

Whooping Cough (Pertussis)
Outbreaks in the U.S. have killed several infants and sickened thousands of adults and kids in the past two years with flulike symptoms and a persistent cough. Making sure your vaccines are up-to-date can lower your risk.

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West Nile Virus
About one in five people infected with this mosquito-borne virus, found throughout the U.S., will develop a fever, rash, headache or joint pain; one in 100 will get a neurological illness such as meningitis. To keep bugs at bay, wear insect repellent containing DEET, get rid of standing water in your yard and screen or close doors and windows.

Chikungunya
This viral infection, spread by the tiger mosquito, was reported in the Caribbean in 2013. This year, eight people were diagnosed in Florida, suggesting that mainland mosquitoes have become infected. Symptoms include fever and joint pain. Protecting yourself from insect bites is your strongest defense.

Flu Prevention Primer

Get a flu vaccine and encourage friends and family to get one as well. Go for a quadrivalent vaccine (in either shot or nasal-spray form) if it's available, since it offers protection against four flu strains rather than three. But if your provider has only the trivalent, get it.

Wash your hands often (use an alcohol-based sanitizer when you're not near a sink) and avoid touching your eyes, nose and mouth—especially after shaking hands or handling doorknobs, railings or keyboards. (According to a small study at the University of California, Berkeley, we touch our faces roughly 16 times an hour!)

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Stay home if you're sick to avoid infecting friends, co-workers and fellow commuters. You can pass the virus on to others for five to seven days after first showing symptoms.