Case B: LL is a 12-year-old female presenting to her pediatrician, complaining o

Question

Case B: LL is a 12-year-old female presenting to her pediatrician, complaining of sore throat and cough. She has had some hoarseness in her voice over the past few days and subjective sweats but no documented fever. She has a history of seasonal allergies in the fall, and takes loratidine (antiallergic) only during that season. Upon review of systems, she complains of isolated throat pain, without any running nose, sinus pressure, or headache. Her mother has been taking her temperature at home, and they have fluctuated from 97.8°F-99.2°F. Throat examination showed yellow pus dots in the back. Rapid Strep Antigen (RSA) Throat Culture Negative Pending

Explanation / Answer

5. Answer: Rapid Strep Antigen Test is used to detect GAS(Group A specific antigens) of Group A beta hemolytic Strep pyogenes. The virulence factors to be detected are Capsule (which inhibits the phagocytosis in the host immune system), Enzymes (Streptokinase, Hyaluronidase, Streptolysin O) and toxins (Erythrogenic toxin, Exotoxin A and Exotoxin B)

Explanation: Eventhough most of the symptoms coincides with the Strep throat, the RSA test in the returned with negative result. This is common for 3-8% of the cases and need throat culture results for confirmation for which the results are pending as per the given question. Assuming that the organism is Strep pyogenes, when gram staining is performed the following would be the expected observations:

6. Strep pyogenes is a gram positive bacterium and hence stained by crystal violet and appears in PURPLE color. Since, they are cocci, they appear as round spherical clusters or short chains, diplococci or single cocci.

Additional information: Strep pyogenes exhibit betahemolytic colonies on Blood agar when incubated for 24 hrs in aerobic conditions at 37 Celsius.

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