What are the potential complications of untreated strep throat infection?

Acute rheumatic fever is a known and serious complication of strep throat. It is thought that if the strep throat infection is untreated or inadequately treated by antibiotics, the bacteria remain in the tonsils and promote a persistent immune response from the body. Certain strains of the bacteria are more likely to cause this response. At times, this ongoing immune response may trigger the immune system to mistakenly attack other organs in the body including the joints and the heart valves, as seen in rheumatic fever.

Treatment with appropriate antibiotics, even if started several days after the resolution of the infection, may prevent acute rheumatic fever. Fortunately, it is now uncommon in the current antibiotic era.

Theoretically, a similar process may cause involvement of the kidneys and result in kidney inflammation called glomerulonephritis (or post-streptococcal glomerulonephritis). There is however, no evidence to support the use of antibiotics to prevent this condition. Children under the age of seven are at the highest risk of developing this condition. This condition is less common and less severe than rheumatic fever. It typically resolves spontaneously after a few weeks and generally does not to lead to permanent kidney damage.

Other complications of untreated strep throat infection include formation of an abscess behind the throat (retro-pharyngeal abscess), which may cause severe pain and illness. These abscesses may need to be drained by an ear-nose-throat specialist urgently.