A 6-year-old boy is brought to the office due to persistent cough. His symptoms began with a mild, upper respiratory illness 2 weeks ago, but the cough has progressively worsened, and now spells of dry cough are often followed by vomiting. The patient has no chronic medical conditions but has not received childhood vaccinations due to parental beliefs. He recently returned from a summer camp. On physical examination, the patient is afebrile, and lungs are clear to auscultation. Testing of respiratory secretions shows gram-negative coccobacilli. Which of the following is most likely involved in the pathogenesis of this patient's symptoms?

Question

A 6-year-old boy is brought to the office due to persistent cough.  His symptoms began with a mild, upper respiratory illness 2 weeks ago, but the cough has progressively worsened, and now spells of dry cough are often followed by vomiting.  The patient has no chronic medical conditions but has not received childhood vaccinations due to parental beliefs.  He recently returned from a summer camp.  On physical examination, the patient is afebrile, and lungs are clear to auscultation.  Testing of respiratory secretions shows gram-negative coccobacilli.  Which of the following is most likely involved in the pathogenesis of this patient's symptoms?

Quizplus · Accepted Answer

Bordetella pertussis, a small, gram-negative coccobacillus, spreads rapidly via airborne droplets through communities with low rates of tetanus-diphtheria-pertussis vaccination. Infants and children are most susceptible and typically develop a few weeks of mucoid rhinorrhea followed by 2-4 weeks of severe, paroxysmal cough, often with an inspiratory whoop and subsequent vomiting. Although the bacterium is largely noninvasive, B pertussis has several virulence factors (eg, pili, filamentous hemagglutinin, pertactin) that allow it to strongly attach to respiratory epithelium. After binding, it then elaborates inflammatory exotoxins, including: Tracheal cytotoxin - directly damages and destroys ciliated epithelial cells, leading to a loss of airway protection, subsequent microaspiration, and development of the characteristic paroxysmal cough. Pertussis toxin - an AB toxin that enters cells and activates adenylate cyclase, leading to alterations in cellular signaling that inhibit phagocyte activity and can cause lymphocytosis. (Choice A) Acute bacterial pneumonia (eg, Streptococcus pneumoniae) presents with fever and productive cough; it is associated with massive migration of neutrophils from the bloodstream into the alveoli. In contrast, pertussis is associated with reduced neutrophil influx due to elaboration of pertussis toxin and adenylate cyclase toxin. (Choice B) Endotoxins are cell-wall components of gram-negative bacteria that can cause septic shock (eg, hypotension, fever, diminished pulses) when released into the bloodstream. Pertussis is noninvasive; disease manifestations are mediated by exotoxins, not endotoxins. (Choice C) Haemophilus influenzae is a small, gram-negative coccobacillus that often causes infection in patients who have not been vaccinated (H influenzae type B vaccine). It is a leading cause of epiglottitis, which typically presents with respiratory distress, tripod posture, and anxiousness. Cough is usually absent. (Choice D) Mycobacterium tuberculosis infection is marked by interferon-gamma-mediated macrophage activation, which leads to the formation of protective granulomas and the killing of the bacteria. M tuberculosis is an acid-fast bacterium; it is not gram-negative. Educational objective: Bordetella pertussis, a small, gram-negative coccobacillus, can cause outbreaks of whooping cough in unvaccinated individuals. Infected infants and children generally develop mucoid rhinorrhea followed by severe, paroxysmal cough that may be associated with an inspiratory whoop and vomiting. The bacterium is largely noninvasive and secretes several exotoxins that severely damage ciliated respiratory epithelium.

A 6-Year-Old Boy Is Brought to the Office Due to Persistent