My son has always been susceptible to strep throat infections, up to three cases a year. He is 23 now and just got another one. The difference this time is that along with his usual symptoms -- fever, sore throat with white coating in his throat, headache -- he also has severe joint pain everywhere. It started with his ankles and even his back is hurting. He is taking amoxicillin for it, but I am concerned about the additional symptoms and their effects on his health. Is this normal?

D.W.

A sore throat might be strep throat (an infection caused by Streptococcus pyogenes bacteria). Or it might be pharyngitis (throat inflammation) caused by viruses. Telling the difference can be difficult, because the two may have overlapping signs and symptoms. Strep throat usually involves fever, a yellowish exudate (coating) on the tonsils and enlarged lymph nodes in the front of the neck. Normally, patients do not have a cough or a stuffy or runny nose. When viruses cause sore throat, the person may have a cough or nasal symptoms and enlarged lymph nodes in the back part of the neck, but usually has less fever and no exudate on the tonsils.

The preferred diagnostic test for strep throat is finding strep bacteria in a culture grown from a swab of the tonsils and throat. It is possible that every time that your son had a sore throat and had a throat culture taken, strep bacteria grew. This could mean that his sore throat was indeed caused by strep infection on all those occasions. However, up to 10 percent or more of healthy people carry strep in their throats. That means if your son is a chronic strep carrier, he may have had frequent viral infections that were misdiagnosed as strep throat, based on a positive culture. To tell the difference, he should have a throat culture performed when he is feeling well. If it is positive, then he is indeed a chronic carrier. In that case, there is usually no need to try to get rid of the strep from his throat because it usually does not cause much trouble.

Regardless of your son's history of strep, what is going on now? It is hard to say, but it's possible he has a viral infection. There are many viruses that can cause sore throat, and some of them can also cause body and joint aches. Influenza is a possibility. The common cold (rhinovirus) can cause sore throat, but fever and aches are not prominent complaints.

Epstein-Barr virus (EBV), the cause of infectious mononucleosis (mono), can cause sore throat, fever and headache. It can even cause exudate in the throat, as well as muscle and joint aches. This is a relatively common disorder, and your son should probably be tested to rule it out. If he has this infection, it is usually nothing to worry about; it just may take him more than a month to fully recover. However, amoxicillin (Amoxil) usually causes a rash when given to people with an acute Epstein-Barr virus infection, so if your son did not have a rash, that makes this diagnosis somewhat less likely.

Another virus that can cause all of your son's symptoms, including the exudate in his throat, is adenovirus. Adenovirus infection commonly occurs in the spring and summer months and causes a severe sore throat. Joint pains are not usually prominent, but they certainly can occur. One clue to this diagnosis is the finding of conjunctivitis (inflammation of the membrane lining the eyes and eyelids, also called pink eye) in someone with a sore throat. There is no real reason to confirm this diagnosis because no treatment is necessary.

Although I can't diagnose your son's condition without examining him personally, I would guess from your description that he probably has a viral infection, either due to EBV or adenovirus. I think that he will recover uneventfully, with or without antibiotics. If he does not get better in a few days, then further workup, including culture and viral testing, is warranted. When he is healthy, his throat should be cultured for strep to determine if he is a chronic carrier.