A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 7-day-old infant boy presents to an emergency department due to poor feeding. His parents are recent immigrants to the United States. He was born in a traditional home birth and has never seen a medical provider. Mom had no prenatal care, has no medical issues, and is unvaccinated. The baby had been breastfeeding well until 24 hours ago when mom noticed he started having trouble latching. In the last 12 hours, he has completely refused to feed. He has had a decreased number of wet diapers and has stooled twice in the last 24 hours. His temperature is 98.6°F (37.0°C), pulse is 180/min, respirations are 52/min, and blood pressure is 70/50 mmHg. On exam, the infant has increased tone, a clenched jaw, no head lag, and clenched hands. Initial screening bloodwork is normal. What is the most likely organism causing this infant's presentation?
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A
Clostridium botulinumIncorrect. Infant botulism (Clostridium botulinum) causes flaccid descending paralysis with hypotonia and constipation — opposite of this rigid, hypertonic presentation.
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B
Clostridium tetaniCorrect. Neonatal tetanus from C. tetani at the umbilical stump in an infant of an unvaccinated mother causes trismus, increased tone, and inability to feed via tetanospasmin blockade of GABA/glycine.
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C
Group B streptococcusIncorrect. Group B strep sepsis causes hypotonia, lethargy, respiratory distress, and fever in a septic-appearing infant — not trismus and hypertonia.
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D
Listeria monocytogenesIncorrect. Listeria neonatal sepsis presents with nonspecific signs of sepsis and meningitis, not the trismus-rigidity pattern of tetanus.
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E
Streptococcus agalactiaeIncorrect. S. agalactiae (group B strep) is the same organism as choice C and causes early-onset neonatal sepsis with hypotonia and respiratory distress — not the trismus and rigidity of neonatal tetanus.
↑ Tap an answer to reveal the reasoning
Answer: B. A 7-day-old infant born at home to an unvaccinated mother, with no prenatal care, presenting with poor feeding, jaw clenching (trismus), increased tone, and difficulty latching — followed by complete inability to feed — has neonatal tetanus from Clostridium tetani infection. The classic risk factor is umbilical stump contamination (often from non-sterile cord cutting or application of unclean substances) plus lack of maternal tetanus immunization (which would have provided passive transplacental antibody).
Neonatal tetanus presents in the first 1–2 weeks of life with trismus (lockjaw), inability to suck (the earliest sign), generalized rigidity, opisthotonus, and stimulus-induced spasms. The mechanism is tetanospasmin — a neurotoxin that travels retrograde up motor axons, enters spinal inhibitory interneurons (Renshaw cells), and blocks release of GABA and glycine. Without inhibitory input, motor neurons fire uncontrollably, producing tonic contractions.
Clostridium botulinum (infant botulism from honey or environmental spores) causes the opposite picture — flaccid descending paralysis with hypotonia, poor feeding, and constipation — not increased tone. Group B strep causes neonatal sepsis/meningitis with hypotonia, fever, respiratory distress. Listeria meningitis causes nonspecific sepsis. Treatment of neonatal tetanus is human tetanus immune globulin (HTIG), metronidazole, supportive care (mechanical ventilation, sedation), and wound care.
**Why each option:**
**A.** Infant botulism (Clostridium botulinum) causes flaccid descending paralysis with hypotonia and constipation — opposite of this rigid, hypertonic presentation.
**B.** Correct. Neonatal tetanus from C. tetani at the umbilical stump in an infant of an unvaccinated mother causes trismus, increased tone, and inability to feed via tetanospasmin blockade of GABA/glycine.
**C.** Group B strep sepsis causes hypotonia, lethargy, respiratory distress, and fever in a septic-appearing infant — not trismus and hypertonia.
**D.** Listeria neonatal sepsis presents with nonspecific signs of sepsis and meningitis, not the trismus-rigidity pattern of tetanus.