美国有线新闻 CNN 致命流感肆虐美国 揭秘四大致命原因（在线收听）

Which of these "seasons" typically coincides with fall and winter in the U.S.?

Baseball season, hurricane season, flu season, or carnival season?

The only one of these seasons that starts in the fall and continues through winter is the flu season.

AZUZ: It's closed down schools in at least 12 states. It set a record for the number of cases in New York state. It's the first time in 15 years that every state in the continental U.S. has reported widespread activity during the same week and it's possible that the current flu season that's ravaging the country hasn't even peaked yet.

Part of the reason is that this year's flu vaccine appears to be one of the least effective in recent years, though doctors say people should still get it because it might make the flu less severe. H3N2 is the specific strain of the virus that's making so many people sick. This strain usually causes higher rates of hospitalizations and death.

ELIZABETH COHEN, CNN SENIOR MEDICAL CORRESPONDENT: It's always scary when you hear of someone dying from something as common as the flu.

There are four main ways the flu can turn deadly.

The first and most common cause is pneumonia. The influenza virus can directly cause viral pneumonia. When someone has the flu, it can weaken their immune system so much that another virus or bacteria can enter the lungs. Infected lungs filled with fluid making it difficult to breathe, so oxygen can't get to the rest of the body which can lead to death.

Sepsis is the second way the flu can become lethal, especially in healthy and younger adults and children. Sepsis occurs when a person's immune system goes into overdrive trying to fight the flu. This causes inflammation which can lead to a cascade of symptoms that ultimately ends in organ failure.

A third way the flu can kill is by increasing your risk of heart attack. Experts say an adult's risk of heart attack increases six-fold in a seven days following a flu diagnosis.

The fourth way the flu can kill is by dehydration, particularly among infants and young children. The flu often causes vomiting and diarrhea which can quickly become life threatening if fluids aren't replaced in the body.

So, if you get the flu, when should you be worried?

Some people have a higher risks for serious complications from the flu, including the elderly, children under the age of 5, pregnant women and those with chronic health problems.

If this is you, make sure you see a doctor. If you're a healthy older child or adult, watch out for sudden dizziness, severe, persistent vomiting, difficulty breathing, pain or pressure in the chest or abdomen, and flu-like symptoms that improve, then return with a fever or worse cough.