A 7-year-old boy is brought to the physician for the evaluation of sore throat for the past 2 days. During this period, he has had intermittent nausea and has vomited once. The patient has no cough, hoarseness, or rhinorrhea. He had similar symptoms at the age of 5 years that resolved spontaneously. He is otherwise healthy. His temperature is 37.9°C (100.2°F), pulse is 85/min, and blood pressure is 108/70 mm Hg. Head and neck examination shows an erythematous pharynx with grayish exudates overlying the palatine tonsils. There is no lymphadenopathy. Rapid antigen detection test for group A streptococci is negative. Which of the following is most appropriate next step in the management of this patient?

Reassurance and follow-up in two weeks

Measurement of antistreptolysin O titer

Measurement of antiviral capsid antigen IgM antibody

You are treating a neonate with meningitis using ampicillin and a second antibiotic, X, that is known to cause ototoxicity. What is the mechanism of antibiotic X?

It binds the 30S ribosomal subunit and inhibits formation of the initiation complex

It binds the 50S ribosomal subunit and inhibits formation of the initiation complex

It binds the 30S ribosomal subunit and reversibly inhibits translocation

It binds the 50S ribosomal subunit and inhibits peptidyltransferase

It binds the 50S ribosomal subunit and reversibly inhibits translocation

A 62-year-old woman presents to the emergency department for evaluation of a spreading skin infection that began from an ulcer on her foot. The patient has type 2 diabetes mellitus that is poorly controlled. On examination, there is redness and erythema to the lower limb with skin breakdown along an extensive portion of the leg. The patient’s tissues separate readily from the fascial plane, prompting a diagnosis of necrotizing fasciitis. What is the exotoxin most likely associated with this patient’s presentation?

Streptococcal pyogenic exotoxin B

Streptococcal pyogenic exotoxin A

An 82-year-old man presents with painless swelling of the neck for the past week. He reports no recent fever, night sweats, or weight loss. He has no significant medical history, and his only medication is daily aspirin. His temperature is 36.8℃ (98.2℉). On physical examination, there are several non-tender lymph nodes, each averaging 2 cm in diameter, which are palpable in the right anterior cervical triangle. No other palpable lymphadenopathy is noted. The remainder of the physical exam is unremarkable. Laboratory studies show the following: Hemoglobin 10 g/dL Leukocyte count 8000/mm3 with a normal differential Platelet count 250,000/mm3 Erythrocyte sedimentation rate 30 mm/h An excisional biopsy of a cervical lymph node reveals the presence of Reed-Sternberg (RS) cells. Computed tomography (CT) scans and positron emission tomography (PET) scans reveal no mediastinal mass or signs of additional disease. Which of the following aspects most strongly indicates a good prognosis for this patient?

Erythrocyte sedimentation rate (ESR)

Leukocyte count and differential

A 10-year-old boy is brought to the emergency department by his parents because of a dull persistent headache beginning that morning. He has nausea and has vomited twice. During the past four days, the patient has had left-sided ear pain and fever, but his parents did not seek medical attention. He is from Thailand and is visiting his relatives in the United States for the summer. There is no personal or family history of serious illness. He is at the 45th percentile for height and 40th percentile for weight. He appears irritable. His temperature is 38.5°C (101.3°F), pulse is 110/min, and blood pressure is 98/58 mm Hg. The pupils are equal and reactive to light. Lateral gaze of the left eye is limited. The left tympanic membrane is erythematous with purulent discharge. There is no nuchal rigidity. Which of the following is the most appropriate next step in management?

Intravenous ceftriaxone and clindamycin therapy

Intravenous cefazolin and metronidazole therapy

A 10-year-old girl with a rash is brought to the clinic by her mother. The patient’s mother says that the onset of the rash occurred 2 days ago. The rash was itchy, red, and initially localized to the cheeks with circumoral pallor, and it gradually spread to the arms and trunk. The patient’s mother also says her daughter had been reporting a high fever of 39.4°C (102.9°F), headaches, myalgia, and flu-like symptoms about a week ago, which resolved in 2 days with acetaminophen. The patient has no significant past medical history. Her vital signs include: temperature 37.0°C (98.6°F), pulse 90/min, blood pressure 125/85 mm Hg, respiratory rate 20/min. Physical examination shows a symmetric erythematous maculopapular rash on both cheeks with circumoral pallor, which extends to the patient’s trunk, arms, and buttocks. The remainder of the exam is unremarkable. Laboratory findings are significant for a leukocyte count of 7,100/mm3 and platelet count of 325,000/mm3. Which of the following is the next best step in the management of this patient?

Discharge home, saying that the patient may immediately return to school

Administer intravenous immunoglobulin (IVIG)

Discharge home, saying that the patient may return to school after the disappearance of the rash

Discharge home with instructions for strict isolation from pregnant women until disappearance of the rash

Group B streptococcal disease — USMLE Lesson

GBS Microbiology - The Beta-Hemolytic Baddie

Streptococcus agalactiae (Group B Strep) Gram stain

Organism: Streptococcus agalactiae, a Gram-positive coccus forming chains.
Culture: Exhibits a narrow zone of β-hemolysis on blood agar.
Key Biochemical Markers:
- Catalase-negative.
- Bacitracin-resistant (differentiates from S. pyogenes).

⭐ CAMP Test Positive: GBS produces a diffusible CAMP factor that synergistically enhances the hemolysis of Staphylococcus aureus, creating a characteristic arrowhead-shaped clearing on blood agar. This is a hallmark identification test.

Transmission & Risks - The Perilous Passage

Primary Source: Maternal rectovaginal colonization.
Transmission: Primarily vertical, occurring either in-utero (ascending infection) or during delivery.

GBS Early-Onset vs. Late-Onset Disease in Neonates

Risk Factors for Early-Onset Disease (EOD):
- GBS bacteriuria at any point during the current pregnancy.
- Preterm delivery (< 37 weeks).
- Prolonged rupture of membranes (PROM) ≥ 18 hours.
- Intrapartum fever ≥ 38°C (100.4°F).

⭐ A previous infant with invasive GBS disease is the most significant risk factor, mandating automatic intrapartum antibiotic prophylaxis (IAP) in subsequent pregnancies.

Clinical Syndromes - Early vs. Late Onset

Feature	Early-Onset Disease (EOD)	Late-Onset Disease (LOD)
Onset	<7 days of life (typically <24-48h)	7 days to 3 months
Source	Maternal genital tract (vertical)	Maternal or nosocomial/community (horizontal)
Presentation	Sepsis, pneumonia, respiratory distress	Bacteremia without a focus, meningitis

⭐ Exam Favourite: Late-onset disease (LOD) is strongly associated with meningitis (~30% of cases), often presenting with subtle signs like poor feeding, irritability, or fever.

Prevention & Treatment - The Prophylaxis Plan

Diagnosis: Gold standard is blood culture. For suspected meningitis, perform CSF analysis.
Treatment: High-dose IV Penicillin G or Ampicillin is the first-line therapy.

⭐ Universal screening via rectovaginal swab is performed between 36+0 and 37+6 weeks of gestation to guide prophylaxis.

High‑Yield Points - ⚡ Biggest Takeaways

Most common cause of neonatal sepsis and meningitis in term infants.

Early-onset disease (EOD) at <7 days is acquired vertically and typically presents with respiratory distress/pneumonia.

Late-onset disease (LOD) at 7-90 days is acquired horizontally and often presents as bacteremia or meningitis.

Universal maternal screening via rectovaginal culture at 35-37 weeks gestation is key.

Intrapartum antibiotic prophylaxis (IAP) with IV Penicillin G is the cornerstone of prevention for colonized mothers.

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