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You may think your cough ought to last no more than a week, but the actual duration of a typical cough is nearly 18 days, and could be more than three weeks, a study finds.

If you’re a victim of this year’s terrible flu, or any of the other nasty bugs causing general respiratory distress, Dr. Mark Ebell sends his sympathies.

But if you’re tempted to head to the doctor to demand drugs for the hacking cough that came with your illness, he’s got another message: Wait a little longer.

A new study shows that although most people think a cough ought to last no more than a week or so, the duration of the most annoying symptom of winter illness is about 18 days -- and could be more than three weeks.

Taking antibiotics in the interim is not only ineffective, it could also prompt dangerous side effects -- and contribute to the country’s growing problem with bugs becoming resistant to the drugs used to treat them.

That’s according to a new study by Ebell, an associate professor at the University of Georgia College of Public Health, which sought to define the gulf between public perception and reality when it comes to coughing.

“A lot of times patients will come to me and they’ve been coughing for four or five days and they’re not getting any better, so they ask for an antibiotic,” he said. “After eight or nine days, they’re still not feeling better, so they ask for an even stronger antibiotic. Then they’ll say, ‘The only thing that really works for me is this really strong antibiotic.’”

The trouble is, antibiotics aren’t actually the solution for most of the 3 million outpatient cases in the U.S. each year in which cough is the chief complaint, or for the more than 4.5 million outpatient cases diagnosed as acute bronchitis or bronchiolitis. More than 90 percent of such cases are viral, not bacterial, which means they won’t respond to the drugs most folks request, according to the Centers for Disease Control and Prevention.

Ebell decided to pursue the study, published Monday in the journal Annals of Family Medicine, after noticing the disconnect between how long people thought coughs should last and how long they actually lingered.

When he surveyed nearly 500 Georgia residents by phone, he found that they predicted that a cough would last between five days and nine days, but generally about a week, depending on the scenario.

A review of 19 published medical studies, however, revealed that the mean duration of any cough was 17.8 days, with a range of 15.3 to 28.6 days.

If a person demanded -- and received -- an antibiotic after he or she had been sick for a week,  the condition might improve several days later -- but not because of the drug, Ebell said.

“Although this outcome may reinforce the mistaken idea that the antibiotic worked, it is merely a reflection of the natural history of acute cough,” he said.

Convincing people of that fact is tough. In Ebell’s study, a quarter of participants thought that antibiotics were "always helpful" and about 44 percent said they were "always or usually" helpful. 

That ignores the reality that antibiotics won't affect viral infections, and also that they can cause harmful side effects, including allergic reactions and the life-threatening gut condition called C. difficile, Ebell said. Plus, overuse of antibiotics is contributing to conditions such as drug-resistant pneumonia and other infections.

Crystal Thompson, a 34-year-old kindergarten teacher in Fort Worth, Texas, says that she’d start to become concerned if a cough lasted more than a few days.

“I would think no longer than a week,” said Thompson, whose family is just now getting over this year’s severe flu. “If it lasted longer than a week, I’d be in to the doctor.”

But Thompson said she also understands the difference between a viral infection and a bacterial one and that she’d follow her doctor’s advice about antibiotics.

In general, Ebell said he tells patients that they likely don’t need an antibiotic unless symptoms turn serious, with shortness of breath, high fever or bloody or rusty phlegm.

It’s important to get the message out about the actual duration of a normal cough, said Dr. Gustavo Ferrer, director of the new cough clinic at the Cleveland Clinic’s Weston, Fla., site. Ferrer, who was not involved with Ebell’s study, praised it as “beautiful” way to remind the public that there’s not a drug solution for every symptom.

“We have come to the conclusion as a population that we don’t want to be sick for one hour,” he said. "In reality, people want those symptoms to go away right away."

Still, cough docs know that patients come for some relief. Ferrer said that antihistamines such as Benadryl can help dry up airways, reduce coughing and help people sleep. Cough drops – especially those with honey and herbs – can help during the day, he added.

Ebell said he and other docs have come up with a range of ways to discourage demand for antibiotics. They’ll call the infection a “chest cold” instead of acute bronchitis. They’ll agree to write an antibiotic prescription -- but then tell patients to wait.

“If you feel that you’re really not going to get them out of the office without a prescription, give them one and say ‘Don’t fill it for a few days,’” he said. “About half never fill it at all.”

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