DEAR DR. DONOHUE: My 12-year-old son is recovering from strep throat. I have some questions about it. I understand that strep throat progresses to rheumatic fever. How can I tell if he’s developing that? Will his heart be permanently affected? – R.C.

ANSWER: A strep throat is a sore throat caused by the Streptococcus bacterium. Strep throats resolve by themselves without any treatment. So, why bother to treat them? For one, treatment slightly shortens the duration of a strep throat. For two, it stops the spread of the strep germ. And for three, and most importantly, treatment prevents rheumatic fever.

Rheumatic fever is a consequence of untreated strep throat in only a small number of patients, but that consequence has significant ramifications. The strep germ doesn’t cause the damage. Antibodies made by the patient’s own body to the strep germ do the dirty work. They can lead to arthritis that isn’t lasting. They also can lead to heart-valve troubles that are lasting.

Penicillin remains the drug of choice for strep throat. It can be given by injection or by tablets.

Recent outbreaks of rheumatic fever have occurred in the United States, but rheumatic fever isn’t the threat that it once was. Partly that’s due to penicillin treatment. Mostly it’s due to better living conditions. When people are not crowded together, the spread of strep is contained.

Your son has been treated. He will not come down with rheumatic fever. You don’t have to look for its signs.

Strep throat constitutes only 15 percent to 30 percent of children’s sore throats. The rest come from viral infections that are not affected by antibiotics. Every sore throat doesn’t, therefore, call for antibiotic treatment.

DEAR DR. DONOHUE: Eight weeks ago, after a five-day Mexican cruise, my husband and I returned home. Two days later, I ran a low-grade fever for 10 consecutive nights. My joints became extremely painful and stiff. After many blood tests and CT scans, both my primary-care doctor and a rheumatologist could not find an answer for my joint pain. Only one test, the sed rate, was abnormally high. My friend is convinced I have lupus. Your opinion? – E.T.

ANSWER: What you describe is not the classic picture for the onset of lupus. A rheumatologist – an arthritis specialist – never fails to check for it. I don’t think your friend is right.

A thought that comes to mind is reactive arthritis. It’s joint inflammation that pops up after an infection, either a digestive or urinary-tract infection. Bacteria like salmonella, shigella and campylobacter can lead to this kind of arthritis. They usually also cause stomach symptoms like diarrhea. Hepatitis is another illness that can cause reactive arthritis. Sometimes infection with the hepatitis virus produces no other symptoms. You could have caught any of these infections during your cruise.

Sed rates are high with infections.

If your joints are not feeling better shortly, go back to your doctors and inquire about reactive arthritis.

DEAR DR. DONOHUE: I would like to know what causes chest pain other than the heart. I have it after I eat at night. – C.

ANSWER: GERD – gastroesophageal reflux (heartburn) – is a big cause of chest pain. Pain that comes on after eating is suggestive of GERD.

However, the causes of chest pain are legion. Esophageal (swallowing tube) disorders, ulcers, gallstones, chest-muscle problems, lung diseases and pleural (covering of the lungs) irritations are other possibilities.

Why have you eliminated the heart as a contender? You must be positive that it isn’t, because heart disease is what kills most people.