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

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

An 8-year-old boy is brought to the physician because of a 7-day history of a progressively worsening cough. The cough occurs in spells and consists of around 5–10 coughs in succession. After each spell he takes a deep, noisy breath. He has vomited occasionally following a bout of coughing. He had a runny nose for a week before the cough started. His immunization records are unavailable. He lives in an apartment with his father, mother, and his 2-week-old sister. The mother was given a Tdap vaccination 11 years ago. The father's vaccination records are unavailable. His temperature is 37.8°C (100.0°F). Examination shows no abnormalities. His leukocyte count is 42,000/mm3. Throat swab culture and PCR results are pending. Which of the following are the most appropriate recommendations for this family?

Administer oral azithromycin to all family members and Tdap vaccination to the father and mother

Administer oral azithromycin to the baby and father and Tdap vaccination to the father

Administer oral azithromycin to all family members and Tdap vaccination to the father

Administer oral erythromycin to all family members and Tdap vaccination to the father

Administer oral trimethoprim-sulfamethoxazole to the father and baby and Tdap vaccination to the father

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.

A 34-year-old poultry worker presents to his physician with a sore throat and a non-productive cough for 2 weeks. His cough is associated with fever. The vital signs include: blood pressure 120/80 mm Hg, heart rate 67/min, respiratory rate 18/min, and temperature 37.6°C (98.0°F). Physical examination shows oropharyngeal erythema and scattered, moist rales on lung auscultation. The patient's X-ray demonstrates patchy reticular opacities in the perihilar regions of both lungs. After some additional tests, he is diagnosed with community-acquired pneumonia and is initially treated with cephalexin with no significant improvement. Which of the following best describes the immune response elicited by the pathogen that is causing this patient's condition?

It primarily induces the Th1-cell response.

Antibody-mediated immunity plays the leading role in the elimination of this pathogen.

Peptidoglycan is its major antigen that induces an immune response.

This pathogen evades the immune response by encapsulation.

It activates TLR5 on the surface of macrophages.

Blood cultures are sent to the laboratory and empiric treatment with intravenous vancomycin is started. Blood cultures grow gram-negative bacilli identified as Cardiobacterium hominis. Which of the following is the most appropriate next step in management?

Switch to intravenous ceftriaxone

Switch to intravenous gentamicin

Switch to intravenous ampicillin

Switch to intravenous cefazolin

Bordetella pertussis for USMLE Step 3: High-Yield Microbiology Lessons

Microbiology & Virulence - The Whoop-There-It-Is Bug

Organism: Encapsulated, gram-negative coccobacillus. Strictly aerobic & fastidious.
Culture: Requires specialized media for growth:
- Bordet-Gengou agar (potato-based).
- Regan-Lowe medium (charcoal, blood, antibiotic).
Key Virulence Factors:
- Filamentous Hemagglutinin (FHA): Mediates adherence to ciliated respiratory epithelium.
- Pertussis Toxin (PT): ADP-ribosylates Giα, disabling it → massive ↑cAMP.
- Adenylate Cyclase Toxin: Exogenous, calmodulin-activated adenylate cyclase → ↑cAMP.
- Tracheal Cytotoxin: Peptidoglycan fragment toxic to ciliated epithelial cells.

⭐ Pertussis toxin (PT) disables Gi proteins, the inhibitory G-protein, leading to uninhibited adenylate cyclase activity. The resulting surge in cAMP is responsible for the profound lymphocytosis seen in patients.

Bordetella pertussis infection and immune response

Pathogenesis & Clinical Stages - The 100-Day Cough

Attachment: Bacteria adhere to the respiratory ciliated epithelium using adhesins like filamentous hemagglutinin and pertactin.
Toxin-Mediated Damage:
- Pertussis Toxin (PT): Disables Gi proteins → massive ↑ cAMP. This impairs immune cell function and causes profound lymphocytosis.
- Adenylate Cyclase Toxin: An invasive enzyme that directly increases intracellular cAMP.
- Tracheal Cytotoxin: A peptidoglycan fragment that is directly toxic to ciliated epithelial cells, causing ciliostasis and their extrusion.

⭐ Pertussis Toxin prevents lymphocytes from entering lymphoid tissues, causing a dramatic peripheral lymphocytosis (WBC >20,000/μL) instead of the neutrophilia typical of bacterial infections.

Diagnosis & Treatment - Taming the Whoop

Diagnosis:
- Gold Standard: PCR from a nasopharyngeal swab is preferred for its speed and sensitivity.
- Culture: Requires specialized media like Bordet-Gengou or Regan-Lowe charcoal agar.
- Labs: Classic finding is a dramatic ↑ in white blood cells, with marked lymphocytosis.
Treatment:
- Antibiotics: Macrolides (e.g., Azithromycin) are the drugs of choice. Crucial to treat early.
- Prophylaxis: Treat all close contacts, regardless of immunization status.
- Supportive care is vital, especially in infants.

⭐ Pertussis toxin causes the profound lymphocytosis by preventing lymphocytes from entering lymphoid tissue.

Bordetella pertussis culture on Regan-Lowe charcoal agar

Prevention - Vaccine Vanguard

Acellular Vaccines (aP):
- DTaP: For children < 7 years old. Contains more pertussis antigens.
- Tdap: Booster for adolescents (age 11-12) and adults. Recommended for all healthcare workers.
Chemoprophylaxis: For close contacts; macrolides (e.g., azithromycin) are effective in preventing disease after exposure.

⭐ Tdap is recommended during each pregnancy, ideally between 27-36 weeks, to provide passive immunity to the newborn.

High‑Yield Points - ⚡ Biggest Takeaways

Bordetella pertussis is a Gram-negative coccobacillus that causes whooping cough.

It attaches to the respiratory epithelium via filamentous hemagglutinin.

Pertussis toxin ADP-ribosylates G_i_, disabling it and leading to a massive ↑ in cAMP, causing lymphocytosis.

The clinical course has three stages: catarrhal, paroxysmal, and convalescent.

Culture requires special media: Bordet-Gengou or Regan-Lowe agar.

Treatment is primarily with macrolides.

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