For many people, the answer to that question is "at least once a year" and the reason is upper respiratory tract infection (URTI). Because of the amount of time and effort involved in isolating precisely what is causing an upper respiratory tract infection, doctors quite frequently prescribe unneeded antibiotics:
Various bacterial respiratory infections were diagnosed during 6.5% of physician office visits in 1999. One or more antibiotics were prescribed during 51.0% of those visits. The probabilities of resistance to the most frequently prescribed antibiotics varied from 20% to 40% and showed a weak positive correlation with the frequencies of antibiotic prescriptions.
It is a well-established fact that a huge percentage of antibiotic prescriptions are dispensed for conditions where they will have no effect, such as the common cold, simply because doctors feel that they have some obligation to write patients a prescription--or because the patients pressure the doctor and insist that they need an antibiotic.
But statistics released in this month's Pharmacist's Letter make the issue very clear. Overtreating with antibiotics does more harm than good.
There's only a 1 in 4000 chance that an antibiotic will help most acute upper respiratory infections.
But there's a 1 in 4 chance of diarrhea...a 1 in 50 chance of a skin reaction...and a 1 in 1000 chance it'll cause an ER visit.
...antibiotics [overuse] can also lead to more resistant infections that are harder to treat.
Now, as always, I encourage readers who believe that they might be suffering from any illness to consult their physicians. But think about those numbers for a second. There's only a 0.025% chance that it's going to do you any good to beg your doctor for an antibiotic prescription. The odds that you will wind up in the ER because of a bad antibiotic reaction are higher than the odds that the antibiotic is going to do you any good.
This does not mean that you should avoid antibiotics at all costs, believing that the risks always outweigh the benefits, because that is patently untrue. Keep in mind that these numbers only pertain to (generally non life-threatening) respiratory infections. What this really mean is that you should ask your doctor to be straight with you, especially if you are going to the doctor because you're coughing up phlegm or have a stuffy head. "Do you really think I need an antibiotic?" Make it very clear that you will take no for an answer if it is that physician's professional opinion that you don't need one. They didn't go to school for nothing.