I am a healthy 42-year-old woman. I have had three cases of strep throat in the past two months. I am volunteering a lot in my kid's classrooms this year, and I blamed it on the germy kids. But now my little Maltese is sick, too. My vet did a throat culture on her. Can a human pass strep to a dog? Can a dog pass strep to a human? I am getting different opinions from my vet and my doctor.

H.

There are several very interesting points to make about your case. First, strep throat is usually caused by an infection with Streptococcus pyogenes, also called "group A strep." This infection causes sore throat, fever and lymph-node swelling in the neck. Sometimes, the illness leads to complications such as abscesses, rheumatic fever and kidney disease. Occasionally, strep throat is caused by other streptococci bacteria, usually "group C strep" or "group G strep." These illnesses are similar to strep throat caused by the usual group A strep.
My first concern would be whether you have had true strep throat. I would expect most people with strep throat to have fever but NOT hoarseness, cough or nasal symptoms. If your symptoms did not follow this pattern, then you may have had viral infections and not strep throat. Viruses such as rhinovirus (the cause of the common cold) are more typical causes of sore throat than strep.

Did you have cultures of your throat during these episodes? Even if all three of your episodes resulted in positive strep cultures, you may not have had strep throat each time. It would be a little unusual for an adult (or a child, for that matter) to develop strep throat so frequently. You might have had a single infection that lasted a long time, but that is not very likely because strep throat is usually a self-limited infection that does not recur even without treatment. Another possibility is that you developed strep throat three different times with three different strains of the bacterium. It is theoretically possible that you got the infection from your dog, but such a case has never been documented conclusively.

I think the most likely explanation is that you did not have strep throat three times. I believe you had viral infections or even noninfectious causes of sore throat. If you had positive cultures for strep each time, then perhaps you are a so-called "strep carrier." Up to 20 percent of people can chronically harbor the bacterium in their throats. Then, anytime you have a throat culture, it will be positive whether you are ill or not. Each time, you will get the diagnosis of strep throat.

How can you determine if you are a chronic carrier? When you are well, with no symptoms, you should have a throat culture. If the culture is positive, then you are very likely a chronic carrier. The good news is that chronic carriers are at little if any risk of any of the complications of strep throat. In most instances, chronic carriers do not need to be treated at all.