Strep (short for Group A Streptococcus) is a bacteria that can cause sore throats in both adults and children. It looks no different than any other type of sore throat, and comes in mild, medium and severe cases. Most sore throats are caused by viruses, so they go away without any treatment. Strep throat is the only type of sore throat that needs antibiotic treatment, because strep might lead to complications that could be severe or life-threatening.
Sore throats caused by other bacteria, or by viruses, should (almost) never be treated with antibiotics. Many good studies have shown that using antibiotics for non-strep sore throats ONLY leads to side effects, bacterial resistance, and absolutely zero effect on the the sore throat.
Signs of strep throat include throat pain, pus on the tonsils, fever, headache, vomiting, stomach ache, and tiredness. These could also be signs of viral sore throat, so you really can’t tell if it is strep without doing a strep test. Two common tests are the throat culture (takes 24 hours, 95% accurate) and the strep antigen test (takes 5 minutes, 95% accurate).
If it is not true strep, a sore throat should not be treated with antibiotics.
Once you prove that group A strep is the cause of the sore throat, you should treat it with a specific antibiotic that is effective against strep. Penicillin (the really yucky tasting stuff) is most effective, so that is a good treatment if you are taking pills. Macrolides (like azithromycin or erythromycin) are the first choice for anyone allergic to penicillin. Other drugs similar to penicillin, like amoxicillin, are also effective. Tetracycline and sulfa-type drugs are NOT effective. Many infectious disease specialists are now recommending cephalosporins for strep to avoid the possibility of your own resistant bacteria destroying any penicillin you take.
Sometimes the strep infection is still there after taking all the antibiotic. There are several possible reasons for this. The widespread abuse of antibiotics has led to bacterial resistance in all of our normal germs (that we carry around in our bodies all the time). These germs produce chemicals that destroy penicillin, so your normal germs might be "protecting" the strep germs by destroying the penicillin. To prevent this, NEVER take antibiotics for viral infections, when they are completely unnecessary. Over half of antibiotics prescribed in the USA are given for inappropriate reasons, and should not be used. Be sure to read the health-byte about "bacterial resistance"!!
Even a mild case of strep throat could lead to heart damage from rheumatic fever, if not treated.
In the last 30 years, the incidence of rheumatic fever, the most severe strep complication, has dropped to very low levels. Checking for strep will prevent this complication, because any strep infection treated within 2-3 weeks will not lead to rheumatic fever. Most cases of rheumatic fever arise from strep throats that did not get checked. You have to remember that strep throat might be a mild case, and might go away in a few days without treatment (but could then go on to rheumatic fever 2 months later!). If in doubt, it is better to get a strep test to know for sure.