**Core Concept**
Group A beta hemolytic streptococci (GABHS) infection can lead to a condition known as **poststreptococcal glomerulonephritis (PSGN)**, a type of kidney inflammation that occurs after a streptococcal infection. PSGN is a classic example of a postinfectious complication.

**Why the Correct Answer is Right**
In the case of a worsening of symptoms despite penicillin treatment, the likely diagnosis is **necrotizing fasciitis**, a severe and life-threatening infection of the soft tissues. This condition requires immediate surgical intervention. The presence of severe swelling, pain out of proportion to the apparent injury, and the progression of disease despite antibiotic treatment are all red flags for necrotizing fasciitis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the worsening of symptoms despite antibiotic treatment. While streptococcal toxic shock syndrome (STSS) is a serious complication of GABHS infection, it typically presents with more systemic symptoms such as hypotension, renal failure, and multi-organ dysfunction.

**Option B:** This option is incorrect because it does not address the worsening of symptoms despite antibiotic treatment. While PSGN can occur after a streptococcal infection, it typically presents several weeks after the initial illness, not concurrently.

**Option C:** This option is incorrect because it does not address the worsening of symptoms despite antibiotic treatment. While a throat abscess is a possible complication of GABHS infection, it typically presents as a localized collection of pus, not a systemic worsening of symptoms.

**Option D:** This option is incorrect because it does not address the worsening of symptoms despite antibiotic treatment. While a retropharyngeal abscess is a possible complication of GABHS infection, it typically presents as a localized collection of pus, not a systemic worsening of symptoms.

**Clinical Pearl / High-Yield Fact**
In cases of worsening symptoms despite antibiotic treatment for GABHS infection, consider the possibility of a more severe infection such as necrotizing fasciitis, and always maintain a high index of suspicion for this condition.

**Correct Answer:** C. The child should undergo immediate surgical evaluation for possible necrotizing fasciitis.