Rheumatic fever is now very uncommon in wealthy societies, but not so in underprivileged and "undeveloped" countries.
The Group A beta-haemolytic Streptococcus can still kill rapidly and cause this immune-mediated after effect.
These notes were scrawled on the back of a Queen Victoria Hospital discharge summary form, in 1966 or 1968. That hospital no longer exists and I've only seen a couple of people with florid acute rheumatic fever in private practice since 1969.
Less severe and less typical instances are still seen, so one still has to think of the possibility.
Prevention depends on avoiding and promptly treating Streptococcal infections. Sore throats are mostly caused by viruses and turn into head colds, but a minority are due to Streptococci (GABHS.)
A good run down on this is at the American Academy of Family Physicians site (http://www.aafp.org/afp/2009/0301/p383.html.)
One simple indication is whether the glands are tender on both sides under the jaw, and if so, where it hurts when you swallow.
Viral sore throats more often have a tender gland on one side only. On swallowing the pain is more often over the glands or right across under the jaw. Strep throats more often have glands tender on both sides and the pain on swallowing is often in the mid-line.
If you can get a look at your throat, marked diffuse reddening and a heavily coated tongue are in favor of Strep throat. If someone is prepared to smell your breath, bad breath ++ also suggests Strep.
Early penicillin treatment certainly reduces our body's antibody response to Streptococcal infection, so hopefully will also reduce the chance of acute rheumatism.The ASLo titre of over 500 in this case reflects past Streptococcal infection. It is not a useful way of telling if a current sore throat is Streptococcal. It is a very useful test if you're prone to frequent sore throats, which may be putting you at risk of this complication if they are Streptococcal.
Streptolysin O is a poison produced by this germ, and anti-streptolysin O is our body's antibody against it.