231. Enhancing the Ability to Detect an Immune Response in Patients with Group A Streptococcal Infections and in the “Carrier” State
Session: Poster Abstract Session: Diagnostic Microbiology
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: Group A streptococci (Streptococcus pyogenes; GAS) cause acute infections, are associated with non-suppurative sequelae (e.g. rheumatic fever, acute glomerulonephritis), or are carried asymptomatically in the throat for extended periods. Throat-culture persistently positive patients who fail to have detectable antibody responses to GAS antigens (e.g. streptolysin O or DNaseB) are termed “carriers.”  Differentiating carriage (organism; no immune response) from infection (organism; immune response) is clinically important for the management and prevention of post-streptococcal complications.

To determine if there has been an immune response to GAS, serum anti-streptococcal antibodies are most commonly measured using one of several techniques, including hemolysis or DNase neutralization, nephelometry, and agglutination assays. The classical neutralization techniques have limitations in that they only can measure antibodies directed at functional domains.  In contrast, enzyme-linked immunosorbent assays (ELISAs) detect antibodies to more epitopes of an antigen, and can be quite sensitive to changes in antibody concentration.  We compared the ELISA and neutralization methods for their capacity to detect immune responses to 2 GAS antigens.

 Methods: An ELISA method was used to measure serum anti-streptolysin O (ASO) and anti-C5a peptidase (anti-SCPA) antibody concentrations in sera obtained from 32 subjects (3-8 serum samples each) followed prospectively for 2 consecutive years.  Changes in these antibodies were compared to changes in ASO and anti-DNaseB titers found by classical neutralization techniques.

Results: 100% of significant ASO rises determined using neutralization methods were also evident by ELISA ASO assays.  Furthermore, of 17 patients who failed to show an ASO response by neutralization, 9 (53%) showed an ASO response by the ELISA.  In 13 (40%) of the 32 subjects, a rise in ASO and/or anti-SCPA was detected by ELISA but not by ASO or anti-DNaseB neutralization methods. 

Conclusion: These data suggest that these ELISA assays increase the capacity to detect immune responses following GAS infections and therefore have practical implications for differentiating host-recognized GAS infection from GAS carriage.

Karen Leopold, Undergraduate student, University of Minnesota College of Biological Sciences, St. Paul, MN, Edward Kaplan, MD, FIDSA, Pediatrics, University of Minnnesota Medical School, Minneapolis, MN, Dwight Johnson, BS, Pediatrics, UNIVERSITY OF MINNESOTA, MINNEAPOLIS, MN; UNIVERSITY OF MINNESOTA, Minneapolis, MN and P. Patrick Cleary, PhD, Microbiology, University of Minnesota, Minneapolis, MN

Disclosures:

K. Leopold, None

E. Kaplan, None

D. Johnson, None

P. P. Cleary, None

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