A 21-year-old Cambodian patient with a history of rheumatic heart disease presents to his primary care physician for a routine check-up. He reports being compliant with monthly penicillin G injections since being diagnosed with rheumatic fever at age 15. He denies any major side effects from the treatment, except for the inconvenience of organizing transportation to a physician's office every month. On exam, the patient is found to have a loud first heart sound and a mid-diastolic rumble that is best heard at the apex. Which of the following is the next best step?

Continue intramuscular penicillin therapy

Switch to intramuscular cefotaxime, which has fewer side effects

Stop penicillin therapy in 4 years

Decrease frequency of injections to bimonthly

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 27-year-old G1P0 female presents for her first prenatal visit. She is in a monogamous relationship with her husband, and has had two lifetime sexual partners. She has never had a blood transfusion and has never used injection drugs. Screening for which of the following infections is most appropriate to recommend this patient?

Syphilis, HIV, HBV, and chlamydia

No routine screening is recommended for this patient

A 28-year-old man presents with painless anal ulcer. Dark-field microscopy shows spirochetes. He is allergic to penicillin with history of anaphylaxis. Which of the following is the most appropriate treatment?

Doxycycline 100 mg orally twice daily for 14 days

Erythromycin 500 mg four times daily for 14 days

Penicillin desensitization followed by benzathine penicillin

A 27-year-old woman, gravida 2, para 1, at 36 weeks' gestation comes to the physician for a prenatal visit. She feels well. Fetal movements are adequate. This is her 7th prenatal visit. She had an ultrasound scan performed 1 month ago that showed a live intrauterine pregnancy consistent with a 32-week gestation with no anomalies. She had a Pap smear performed 1 year ago, which was normal. Vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 36-week gestation. Her blood group and type is A negative. Which of the following is the most appropriate next step in management?

Transabdominal doppler ultrasonography

A 27-year-old woman, gravida 2, para 1, at 37 weeks' gestation is admitted to the hospital in active labor. She has received routine prenatal care, but she has not been tested for group B streptococcal (GBS) colonization. Pregnancy and delivery of her first child were complicated by an infection with GBS that resulted in sepsis in the newborn. Current medications include folic acid and a multivitamin. Vital signs are within normal limits. The abdomen is nontender and contractions are felt every 4 minutes. There is clear amniotic fluid pooling in the vagina. The fetus is in a cephalic presentation. The fetal heart rate is 140/min. Which of the following is the most appropriate next step in management?

Administer intrapartum intravenous penicillin

Obtain vaginal-rectal swab for nucleic acid amplification testing

Obtain vaginal-rectal swab for GBS culture

Obtain vaginal-rectal swab for GBS culture and nucleic acid amplification testing

Group B streptococcus screening — USMLE Lesson

GBS Basics - The Silent Invader

Pathogen: Streptococcus agalactiae, a gram-positive coccus that colonizes the maternal gastrointestinal and genitourinary tracts.
Clinical Significance: A leading cause of neonatal morbidity and mortality, primarily through vertical transmission during labor.
- Early-onset disease (<7 days): Sepsis, pneumonia.
- Late-onset disease (7-89 days): Meningitis, bacteremia.

⭐ GBS is the most common cause of early-onset neonatal sepsis, typically presenting within the first 24-48 hours of life.

Screening Protocol - The Swab Story

Universal screening for all pregnant women to reduce neonatal GBS disease.

Who: All pregnant women.
When: 36 0/7 - 37 6/7 weeks of gestation.
How: Rectovaginal culture. A single swab is passed over the lower vagina (introitus) and then through the external anal sphincter.

⭐ Exam Favorite: A patient with GBS bacteriuria at any point during the current pregnancy is automatically considered colonized. They do not require a rectovaginal screen and should be scheduled for intrapartum antibiotic prophylaxis.

Prophylaxis Plan - Antibiotic Action

⭐ Penicillin G is the first-line antibiotic for GBS IAP. For patients with a non-anaphylactic penicillin allergy, Cefazolin is the recommended alternative.

IAP Not Indicated: For women undergoing a planned cesarean section before the onset of labor and with intact membranes, regardless of their GBS colonization status.

Drug Regimens - The Backup Crew

Intrapartum antibiotic prophylaxis (IAP) is crucial. The choice of agent hinges on penicillin allergy history and severity.

⭐ Clindamycin resistance is increasingly common in GBS. If susceptibility testing is not available, vancomycin is the preferred agent for high-risk penicillin-allergic patients.

High‑Yield Points - ⚡ Biggest Takeaways

Universal screening for all pregnant women via rectovaginal culture at 36‑38 weeks gestation.

Intrapartum antibiotic prophylaxis (IAP) is indicated for a positive GBS screen, GBS bacteriuria during pregnancy, or a history of a neonate with invasive GBS disease.

IAP is not needed for a planned cesarean delivery performed before labor onset and with intact membranes, regardless of GBS status.

Penicillin is the first‑line antibiotic for IAP.

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