Caused by the bacteria Streptococcus pyogenes (“Strep”). Out of all the sore throats people get, only about 10% are due to this, while the others are caused by viruses (see Differences Among Germs). Sometimes Strep also causes a light rough-feeling rash called Scarlet Fever; 100 years ago, that strain of the bacteria was very severe, but not anymore.
Strep is more common among children and teens than adults. We suspect it if 3 of the following are present:
- Swollen glands
- Pus on the tonsils
- There’s no cough or runny nose
We diagnose Strep by swabbing the throat and doing one of 2 tests, a rapid antigen test, or a culture. The rapid test (5 minutes) is 90% to 95% accurate, but may miss a few cases. The culture won’t miss any, but takes 1-2 days. Another problem with all tests, the culture maybe more so, is that some people are colonized with Strep, meaning it lives harmlessly in the throat without causing disease. So if that person has a virus, the throat swab will be false-positive. We especially suspect this in patients who have “strep throat” over and over.
Strep Throat usually only lasts 3-5 days, and goes away by itself (if it’s lasted longer, it’s very unlikely to be Strep). Because it’s so short-lived, it’s hard to prove that antibiotics help symptoms get better sooner. But we still treat Strep so it doesn’t get spread, and because it can cause complications:
The Strep bacteria can spread deeper into the throat, causing serious illness. But this is very rare. Strep can also trigger an unusual autoimmune reaction that damages the kidneys (“glomerulonephritis”). But we don’t “worry” about this because 1) it almost always gets better on its own; and 2) treating Strep with antibiotics won’t prevent it, so there’s nothing we can do anyway. However, we do worry about Rheumatic Fever, the main reason to treat Strep Throat.
Rheumatic Fever, also an autoimmune reaction, can cause serious heart damage. It’s very rare today (though still present in inner cities and in poor countries), and virtually never occurs after 30 years old (unless the person already had it as a child). Treating Strep Throat within nine days will prevent Rheumatic Fever.