ATLANTA (AP) -- Whooping cough was once a terrible menace to U.S. children, with hundreds of thousands of cases reported annually. Then a vaccine drove cases down, and the illness became thought of as rare and even antiquated.

But it never totally disappeared, and now there's been a spike in cases.

With nearly 18,000 cases so far this year, health officials say this is shaping up to be the worst national epidemic in more than 50 years for the highly contagious disease.

Worrisome numbers have been reported in more than a dozen states.

What's a parent to do?

Some advice:

FIRST STEP: Make sure your child is up-to-date on vaccination against whooping cough, or pertussis. There are five doses, with the first shot at age 2 months and the last between 4 and 6 years. A booster shot is recommended around 11 or 12. It's part of routine childhood shots that also protect against diphtheria and tetanus.

PROTECT YOURSELF: Adults who are around kids should get a whooping cough booster shot so that they don't spread it to young children, who are the most vulnerable to whooping cough. Nine young children have died so far this year. The booster for teens and adults, approved in 2005, was combined with the tetanus booster that adults are supposed to get every 10 years or so.

VACCINE NOT PERFECT: No vaccine is 100 percent effective, and its ability to fend off infections wanes as years pass. But even diminished vaccine protection is better than nothing, and usually people who are vaccinated have milder cases. In this current epidemic, experts are investigating whether the childhood shots and the booster offer less lasting protection than previously thought.

WATCH FOR SYMPTOMS: The illness typically starts with cold-like symptoms that can include a runny nose, congestion, low-grade fever and a mild cough. Infants may have a pause in breathing, called apnea. The Centers for Disease Control and Prevention advises parents to see a doctor if they or their children develop prolonged or severe coughing fits, vomiting and exhaustion.

The name comes from the sound children make as they gasp for breath. Here's what it sounds like: http://tinyurl.com/btskus

The disease is spread through coughing or sneezing. Whooping cough is treated with antibiotics, the earlier the better.

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