Pertussis

A 3-week-old infant stops breathing between coughing spells — but never makes the classic 'whoop.' Pertussis in babies doesn't sound like the textbook because they're too small to whoop.

Pertussis (whooping cough) is caused by Bordetella pertussis, a gram-negative bacterium. It progresses through three distinct phases. Catarrhal phase (1–2 weeks): resembles a common cold with rhinorrhea, mild cough, low-grade fever. This is the MOST contagious phase and the one most often missed. Paroxysmal phase (2–6 weeks or longer): severe coughing fits (paroxysms) followed by a forceful inspiratory 'whoop,' post-tussive vomiting, and cyanosis. Between paroxysms the patient may appear well. Convalescent phase (weeks to months): gradual resolution of cough frequency and severity. Critical age-related distinction: infants under 6 months — especially those too young for vaccination — may NOT produce the characteristic whoop. Instead, they present with apnea, cyanosis, and difficulty feeding. Pertussis is a leading cause of vaccine-preventable infant death. Diagnosis: nasopharyngeal swab for PCR (preferred) or culture (gold standard but slow). Treatment: azithromycin is first-line, including for young infants (monitor for infantile hypertrophic pyloric stenosis risk in neonates). Erythromycin or clarithromycin are alternatives in some patients. TMP-SMX is an alternative only for patients ≥2 months who cannot take macrolides — it is avoided in younger infants due to kernicterus risk. Antibiotics reduce transmission but do NOT significantly shorten illness duration if started after the paroxysmal phase begins. Droplet precautions until 5 days of appropriate antibiotics are completed. Prevention — the most tested content area: DTaP vaccine for children (5-dose series). Tdap for adolescents and adults. Tdap in EVERY pregnancy at 27–36 weeks gestation regardless of previous Tdap history — this transfers maternal antibodies to the newborn, providing passive protection during the most vulnerable period before the infant's own vaccination can begin at 2 months. Cocooning strategy: vaccinate all household contacts and caregivers of newborns. Pertussis is a nationally notifiable disease. Nursing: suction equipment at bedside, small frequent meals to reduce post-tussive vomiting, monitor infant oxygen saturation during and between paroxysms, provide calm quiet environment (agitation worsens coughing), and educate families that cough may persist for months during convalescence.

Key Distinctions

Tdap every pregnancy (27–36 weeks) regardless of prior vaccination is the #1 tested point — students often think one Tdap dose confers lifelong protection, but maternal antibody transfer requires re-vaccination each pregnancy. Infants may present with apnea rather than whooping cough — absence of the whoop does NOT rule out pertussis in infants. The catarrhal phase is the most contagious but looks like a cold — by the time the whoop appears, the diagnosis is often delayed. Do not confuse DTaP (childhood formulation, higher antigen dose) with Tdap (adolescent/adult formulation, lower antigen dose). TMP-SMX is contraindicated in infants under 2 months due to kernicterus risk.

Clinical Pearl

Every pregnancy gets Tdap at 27–36 weeks. Every one. Even if the patient had it last pregnancy. The baby needs those antibodies fresh.