Anistreptolysin-O: A Literature Review

Summary

Streptococcus pyogenes (group A Strepto­coccus, GAS) is one of the most common pathogens, which can cause a wide range of infections from uncomplicated selflimited pharyngotonsillitis or impetigo to very serious diseases like rheumatic fever, acute glomerulonephritis, streptococcal toxic shock syndrome. Swabbing the throat and testing for GAS pharyngi­tis by rapid antigen detection test and/or culture are both the gold standard to con­firm the di ag no sis of strepto coc cal pharyngotonsillitis. The onset of non- suppurative complications of GAS infec­tions often starts several weeks after an acute infection when symptoms and signs are resolved. Throat cultures taken at this time may be negative because of clearance of GAS by the host immune system during the latent period or due to previous antibiotic treatment. The evi­dence of recent preceding streptococcal infection can be proved by serological tests, one of which is measurement of antistreptolysin O con cen tration. Streptolysin O acts in human organism as antigen, triggering the production of antistreptolysin O antibodies, which con­centration begins to increase within 1 week and reaches the peak at 3-6 weeks. They start to gradually de­crease 6-8 weeks after and reach their previous level after 12-18 months. The normal ASO values vary depending on the age of child, geographic location, sea­son, use of antibiotics and steroids. Other antibodies - antideoxyribonucleasis B are more specific to A group streptococcal infections, because streptolysin-O is also produced by C and G streptococci. Estimation of ASO and ADB concentrations can be helpful when rheumatic fever, acute glomerulonephritis, paediatric autoimmune neuropsychiatric disorder associated with group A streptococci (PANDAS) are suspected. However ASO concentration cannot be elevated in 20% of patients with preced­ing severe streptococcal infections. For this reason, the ADB concentration is recommended additionally to prove re­cent streptococcal infection. The aim of this article is to acquaint physicians with avail able streptococcal serological tests, their clinical benefit and interpretation of their results.

Conclusions: The ASO concentra­tion is useful, if complications of streptococcal origin are suspected. It shows pre­vious streptococcal infection, however is not always absolutely precise: a negative result does not always show the absence of previous streptococcal infection, though an increased one does not always mean there was a group A streptococcal infection. The ADB concentration is more specific than ASO concentration for GAS caused disease, so we recommend start­ing to measure ADB concentration in Lithuania. Increased ASO and/or ADB concentrations are not an indication for antimicrobial treatment and/or tonsillectomy.

Keywords: group A Streptococcus (GAS), antistreptolysin O (ASO) concentration, normal values of serological tests, streptococcal diseases diagnostics.