A 40-year-old pregnant woman, G4 P3, visits your office at week 30 of gestation. She is very excited about her pregnancy and wants to be the healthiest she can be in preparation for labor and for her baby. What vaccination should she receive at this visit?

Tetanus, diphtheria, and acellular pertussis (Tdap)

Measles, mumps, and rubella (MMR)

Live attenuated influenza vaccine

A 40-year-old man is brought to an urgent care clinic by his wife with complaints of dizziness and blurring of vision for several hours. His wife adds that he has had slurred speech since this morning and complained of difficulty swallowing last night. His wife mentions that her husband was working outdoors and ate stew with roasted beef and potatoes that had been sitting on the stove for the past 3 days. The patient's past medical history is unremarkable. A physical examination reveals right eye ptosis and palatal weakness with an impaired gag reflex. Cranial nerve examination reveals findings suggestive of multiple cranial nerve involvement. What is the mechanism of action of the toxin that is the most likely cause of this patient's symptoms?

Inhibition of the release of acetylcholine

Ribosylation of eukaryotic elongation factor-2

An 11-year-old boy is brought to his pediatrician by his parents for the routine Tdap immunization booster dose that is given during adolescence. Upon reviewing the patient’s medical records, the pediatrician notes that he was immunized according to CDC recommendations, with the exception that he received a catch-up Tdap immunization at the age of 8 years. When the pediatrician asks the boy’s parents about this delay, they inform the doctor that they immigrated to this country 3 years ago from Southeast Asia, where the child had not been immunized against diphtheria, tetanus, and pertussis. Therefore, he received a catch-up series at 8 years of age, which included the first dose of the Tdap vaccine. Which of the following options should the pediatrician choose to continue the boy’s immunization schedule?

A single dose of Tdap vaccine at 13 years of age

A single dose of Td vaccine at 18 years of age

A single dose of Td vaccine now

A single dose of Tdap vaccine now

A 27-year-old man presents to the emergency department with unrelenting muscle spasms for the past several hours. The patient’s girlfriend states that he started having jaw spasms and soreness last night but now his neck, back, and arms are spasming. She also states that he stepped on a nail about 1 week ago. Past medical history is noncontributory. The patient's vaccination status is unknown at this time. Today, the vital signs include temperature 39.1°C (102.4°F), heart rate 115/min, blood pressure 145/110 mm Hg, and respiratory rate 10/min. On exam, the patient is in obvious discomfort, with a clenched jaw and extended neck. Labs are drawn and a basic metabolic panel comes back normal and the white blood cell (WBC) count is moderately elevated. Which of the following is the most likely etiology of this patient’s symptoms?

An exotoxin that cleaves SNARE proteins

An exotoxin that causes ADP-ribosylation of EF-2

An edema factor that functions as adenylate cyclase

A heat-labile toxin that inhibits ACh release at the NMJ

A toxin that disables the G-protein coupled receptor

A 34-year-old gravida 5, para 4 presents to the physician for prenatal care at 32 weeks of pregnancy. She comes from a rural region of Ethiopia and did not have appropriate prenatal care during previous pregnancies. She has no complaints of swelling, contractions, loss of fluid, or bleeding from the vagina. During her current pregnancy, she has received proper care and has completed the required laboratory and instrumental tests, which did not show any pathology. Her blood pressure is 130/70 mm Hg, heart rate is 77/min, respiratory rate is 15/min, and temperature is 36.6°C (97.8°F). Her examination is consistent with a normal 32-weeks’ gestation. The patient tells the physician that she is going to deliver her child at home, without any medical aid. The physician inquires about her tetanus vaccination status. The patient reports that she had tetanus 1 year after her first delivery at the age of 16, and it was managed appropriately. She had no tetanus vaccinations since then. Which of the following statements is true?

The patient should receive at least 2 doses of tetanus toxoid within the 4-week interval to ensure that she and her baby will both have immunity against tetanus.

The antibodies from tetanus immune globulin vaccine, if given to a pregnant woman, would not cross the placental barrier.

Even if the patient receives appropriate tetanus vaccination, it will be necessary to administer toxoid to the newborn.

The patient is protected against tetanus due to her past medical history, so only the child is at risk of developing tetanus after an out-of-hospital delivery.

The patient does not need vaccination because she has developed natural immunity against tetanus and will pass it to her baby.

A 9-year-old girl presents with a 3-week history of cough. Her mother reports that initially, she had a runny nose and was tired, with a slight cough, but as the runny nose resolved, the cough seemed to get worse. She further states that the cough is dry sounding and occurs during the day and night. She describes having coughing spasms that occasionally end in vomiting, but between episodes of coughing she is fine. She reports that during a coughing spasm, her daughter will gasp for air and sometimes make a “whooping” noise. A nasopharyngeal swab confirms a diagnosis of Bordetella pertussis. Which of the following statements apply to this patient?

Her 3-month-old brother should be treated with azithromycin as prophylaxis.

She should be started on azithromycin for more rapid resolution of cough.

Her classmates should be treated with clarithromycin as prophylaxis.

She will have lifelong natural immunity against Bordetella pertussis.

Her classmates should receive a Tdap booster regardless of their vaccination status.

Diphtheria, tetanus, pertussis for USMLE Step 3: High-Yield Microbiology Lessons

Diphtheria - The Strangling Angel

Organism: Corynebacterium diphtheriae (Gram-positive, club-shaped rod).
Pathophysiology: Exotoxin encoded by a β-prophage inhibits protein synthesis.
Clinical Features:
- Local: Sore throat, fever, and a thick, gray, adherent pseudomembrane on the tonsils/pharynx that bleeds when scraped.
- Systemic: "Bull neck" from cervical adenopathy, myocarditis, and neuropathies.
Diagnosis: Culture on Tellurite or Loeffler's agar; Elek's test for toxin production.
Treatment: Urgent administration of diphtheria antitoxin plus antibiotics (e.g., erythromycin or penicillin).

⭐ The exotoxin inactivates Elongation Factor-2 (EF-2) via ADP-ribosylation, halting protein synthesis.

Diphtheria pseudomembrane in pharynx

Tetanus - The Rigid Smile

Organism: Clostridium tetani - Gram-positive, spore-forming rod (tennis racket appearance), obligate anaerobe found in soil.
Toxin: Tetanospasmin, a protease that travels via retrograde axonal transport to the spinal cord.

⭐ Mechanism: Tetanospasmin cleaves synaptobrevin (a SNARE protein), irreversibly blocking the release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells.

Clinical: Presents with spastic paralysis.
- Trismus (lockjaw) is a common early sign.
- Risus sardonicus (rigid, grinning smile).
- Opisthotonus (arched back).

Ablett Classification of Tetanus Severity

Pertussis - The 100-Day Cough

Organism: Bordetella pertussis, a gram-negative coccobacillus.
Transmission: Respiratory droplets; highly contagious.
Clinical Stages:
- Catarrhal (1-2 wks): Nonspecific symptoms, highest infectivity.
- Paroxysmal (2-8 wks): Inspiratory "whoop," post-tussive emesis.
- Convalescent (1-3 mos): Gradual symptom resolution.
Diagnosis: PCR or culture (nasopharyngeal swab).
Treatment: Macrolides (e.g., Azithromycin).

⭐ Exam Favorite: Pertussis toxin ADP-ribosylates and inactivates Gi proteins, preventing them from inhibiting adenylate cyclase. The resulting surge in cAMP causes massive lymphocytosis by preventing lymphocyte entry into lymph nodes.

DTPH Vaccines - Acellular Shield

DTaP (Diphtheria, Tetanus, acellular Pertussis): Primary series for children <7 years.
Tdap (Tetanus, diphtheria, acellular Pertussis): Booster for adolescents & adults; features lower diphtheria/pertussis antigen dose.
- Administer one dose, then Td booster every 10 years.
Mechanism: Toxoid-based vaccines that stimulate humoral immunity against bacterial toxins.

⭐ Tdap is recommended during each pregnancy (27-36 weeks) to confer passive immunity to the neonate.

Tetanus vaccine schedule by age group (DTaP, Tdap, Td)

High‑Yield Points - ⚡ Biggest Takeaways

Diphtheria toxin inactivates Elongation Factor-2 (EF-2) via ADP-ribosylation, halting protein synthesis.

Tetanus toxin cleaves SNARE proteins, blocking the release of inhibitory neurotransmitters GABA and glycine, causing spastic paralysis.

Pertussis toxin ADP-ribosylates Gi, leading to increased cAMP levels and the characteristic "whooping cough".

Key presentations: Diphtheria's pharyngeal pseudomembrane and myocarditis; Tetanus's trismus (lockjaw).

The DTaP/Tdap vaccine uses toxoids for diphtheria/tetanus and acellular pertussis antigens.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play