Antibody to streptococcal cysteine proteinase as a seromarker of group A Streptococcal (Streptococcus pyogenes) infections

Serological tests are commonly employed to aid the diagnosis of Streptococcus pyogenes infections, particularly when non-suppurative sequelae are suspected. Conventional laboratory practice is to measure antibody levels to various combinations of the extracellular group A Streptococcus (GAS) antigens streptolysin O (SLO), DNase B, streptokinase and hyaluronidase. Antibody to the extracellular cysteine proteinase streptococcal pyrogenic exotoxin B (SPE B) and its precursor zymogen is also produced in response to GAS infections. An indirect hemagglutination test for antibody to zymogen/SPE B was established and evaluated in serum samples from 168 patients with proven (n = 27) or suspected GAS (n = 141) infections, which were also screened for antibodies using the 4 conventional tests. For comparison, sera from 56 patients infected with a variety of other pathogens, as well as sera from 16 patients infected with either S. agalactiae or S. pneumoniae and 34 sera from healthy subjects, were tested. Statistical analysis confirmed that antibody to zymogen/SPE B is a serological marker that can discriminate GAS infections. It can be ranked with the anti-SLO titer, currently the most widely used test, as a marker of an antecedent GAS infection.