Pertussis — formative SAQs

SAQ 1 (10 marks)

A 10-week-old ex-term infant is brought to the emergency department after an episode at home in which the mother describes the baby "going blue and stopping breathing" after a bout of coughing. On assessment the infant is pink, afebrile, and feeding, with clear chest sounds and oxygen saturation of 97% in air. The mother has had a persistent cough for three weeks, and the infant has received only the first DTaP dose at six weeks. The full-blood count shows a lymphocyte count of 18 × 10⁹/L. [8]

Question: Outline the immediate and stepwise management of this infant, including diagnosis, supportive care, treatment, infection control and the public-health response. (10 marks) [1]

Model answer

Recognition and disposition (2 marks). This infant is at the highest-risk end of pertussis — under six months, under-vaccinated, with apnoea/cyanosis and a household cough contact. Even though the infant looks well between events, admit to a monitored bed for continuous apnoea and oxygenation monitoring; have a low threshold for PICU involvement if apnoea, cyanosis or exhaustion recurs. The marked lymphocytosis supports pertussis. [8]

Diagnosis (2 marks). Send a nasopharyngeal aspirate or flocked nasopharyngeal swab for pertussis PCR — the test of choice in the first three to four weeks of illness, when sensitivity is highest. The household contact history and the infant's apnoea make the clinical diagnosis likely while the PCR is pending. Do not delay management while waiting for the result. [1]

Supportive care (2 marks). Give supplemental oxygen for desaturation, use gentle suctioning, minimise stimulation to avoid triggering paroxysms, and support feeds and hydration with small frequent feeds, nasogastric feeding or intravenous fluids as needed. Monitor continuously for apnoea and be ready to escalate to respiratory support. [8]

Treatment (2 marks). Start a macrolide — azithromycin first-line, given over five days. State the purpose honestly: the macrolide's principal role is to limit the infectious period and protect contacts; it rarely shortens the paroxysmal course once established. In a neonate under two weeks, azithromycin is preferred over erythromycin because of the infantile-hypertrophic-pyloric-stenosis risk. [4]

Infection control and public health (2 marks). Isolate with droplet precautions and exclude until five days of effective antibiotic. Notify public health, trace household and close contacts, and offer chemoprophylaxis to high-risk contacts — including the mother, any unvaccinated siblings, and any pregnant household contact. Give catch-up vaccination to under-immunised contacts to complete the cocoon around the infant, and reinforce that maternal Tdap in future pregnancies protects the next infant from the first weeks of life. [10] [9]

SAQ 2 (10 marks)

Question: A 7-year-old fully vaccinated child presents with a two-week history of worsening cough in paroxysms, ending in an inspiratory whoop and post-tussive vomiting. The child is afebrile, well between paroxysms, and has a clear chest. (a) What is the likely diagnosis and how will you confirm it? (b) Outline the treatment, infection-control and public-health management. (c) Explain why a fully vaccinated child can still develop pertussis, and how this informs prevention. (10 marks) [1]

Model answer

(a) Diagnosis and confirmation (3 marks). The likely diagnosis is pertussis, suggested by the paroxysmal cough, the inspiratory whoop, post-tussive vomiting and the two-week duration. Confirm with PCR of a nasopharyngeal aspirate or swab if within the first three to four weeks of illness; if the cough has lasted longer, serology (anti-pertussis-toxin IgG) is the more sensitive test. The child is in the paroxysmal stage and most contagious early in the illness. [1]

(b) Treatment and public-health management (4 marks). Give a macrolide — azithromycin first-line for five days — principally to reduce infectiousness. Isolate with droplet precautions and exclude from school until five days of effective antibiotic (or for three weeks from paroxysm onset if untreated). Notify public health, and trace household and close contacts; identify any infant under twelve months, pregnant woman, or unvaccinated contact and offer chemoprophylaxis promptly. Give catch-up vaccination to any under-immunised contacts. [4] [10]

(c) Why the vaccinated child is still at risk, and prevention (3 marks). Immunity after the acellular pertussis vaccine wanes over time — faster than after the whole-cell vaccine — so a fully vaccinated older child can still develop pertussis, and the same waning immunity in adolescents and adults sustains transmission to infants. Prevention therefore relies on more than childhood priming: an adolescent Tdap booster, maternal Tdap in every pregnancy (which transfers antibody to the infant before birth), high coverage, and cocooning of household contacts. A suggestive cough in a vaccinated child still warrants testing, because the resurgence epidemiology makes pertussis plausible despite complete primary vaccination. [1] [8]