Clinical serology for streptococcal disease: Which of the following laboratory tests can be used to establish a retrospective diagnosis of a recent Streptococcus pyogenes (group A streptococcal) infection, by detecting the host’s antibody response after the acute phase?

Introduction / Context:Post-streptococcal sequelae such as acute rheumatic fever and post-streptococcal glomerulonephritis often present weeks after the throat or skin infection has resolved. Because the organism may no longer be recoverable by culture, clinicians rely on serologic tests that demonstrate a recent immune response to Streptococcus pyogenes antigens.

Given Data / Assumptions:

• The question asks which tests establish retrospective (post-infection) diagnosis.
• Anti-DNase B, ASO (anti-streptolysin O), and Streptozyme are common serologic assays for group A streptococcal exposure.
• These tests measure antibodies, not the organism itself.

Concept / Approach:

Retrospective diagnosis requires evidence of a preceding infection. Antibody titers against secreted streptococcal enzymes rise 1–3 weeks after infection. Anti-DNase B is especially helpful after skin infection; ASO is classically elevated after pharyngitis; the Streptozyme slide test screens for multiple antistreptococcal antibodies.

Step-by-Step Solution:

Verification / Alternative check:

Typical patterns: ASO rises after throat infections; Anti-DNase B is useful after impetigo; Streptozyme provides a rapid qualitative screen. Rising titers or a high single titer in the appropriate time window supports recent infection.

Why Other Options Are Wrong:

Anti-DNase B alone is correct but incomplete compared with using multiple assays.

ASO alone misses some skin infections where ASO responses may be muted.

Streptozyme alone is a screen and may need confirmation; relying on one test is less comprehensive than selecting all applicable tests.

Common Pitfalls:

Equating throat culture positivity with retrospective proof; cultures reflect current carriage, not past infection. Also, interpreting a single borderline titer without clinical correlation or paired sera can mislead.

Final Answer:

All of these