Vaccine-preventable disease outbreak response — formative SAQs

SAQ 1 (10 marks)

A 6-year-old child presents to the emergency department with four days of fever, cough, coryza and conjunctivitis. This morning a blotchy maculopapular rash appeared behind the ears and is spreading cephalocaudally. The child has never been vaccinated. The child attends a school where several other unvaccinated children have had a similar illness. In the waiting room there are infants and a woman who is 28 weeks pregnant. [3]

Question: Outline the immediate and stepwise outbreak response, including the management of the index case, the contact network and the prevention campaign. (10 marks) [1]

Model answer

Recognise, isolate and protect the waiting room (2 marks). This is classic measles — the 3 C's with Koplik-spots-equivalent prodrome and a cephalocaudal rash in an unvaccinated child with a school cluster. The single most important immediate act is airborne isolation (negative-pressure where available) and removal of the case from the waiting room, because measles lingers in the air for up to two hours. Identify the exposed waiting-room contacts, especially the pregnant woman and the infants, because they are the high-risk contacts who drive the prophylaxis triage. [3] [1]

Confirm and notify (2 marks). Confirm with measles IgM on a single serum plus RT-PCR and genotype on a throat/nasopharyngeal swab and urine; the genotype links the case to the school cluster and distinguishes imported from endemic transmission. Notify public health on clinical suspicion — do not wait for confirmation — because notification triggers the contact-tracing and prophylaxis cascade. [1] [2]

Build and triage the contact list (2 marks). Map the school, childcare, household and waiting-room exposures, and triage every contact by risk: who is pregnant (and at what gestation), who is under 6 to 12 months, and who is immunocompromised. These are the contacts who pay most for delay and who are prioritised for same-day prophylaxis. Document the infectious period — from four days before to four days after the rash — to define who was exposed. [2] [6]

Deliver post-exposure prophylaxis within the window (2 marks). Offer MMR within 72 hours of exposure to susceptible contacts; give normal human immunoglobulin within 6 days to the high-risk contacts who cannot receive the live vaccine — the pregnant woman, the immunocompromised child, and infants under 6 to 12 months. The window is narrow, so the contact-tracing effort must reach the high-risk contacts first. Exclude cases until four days after the rash and susceptible contacts through the incubation period. [1] [2]

Prevent — the catch-up campaign (2 marks). Run ring and catch-up vaccination across the affected school and community to lift two-dose coverage back above the herd-immunity threshold of about 95 per cent. The outbreak ends when the susceptible pool is closed, and the campaign is what closes it — as the Amish-community outbreak showed, rapid identification and aggressive vaccination interrupt transmission. Communicate honestly with the community, address vaccine hesitancy respectfully, and document so the programme learns. [7] [11]

SAQ 2 (10 marks)

A 7-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 between events, afebrile, and feeding, with clear chest sounds. The mother and an older sibling have had a persistent cough for three weeks. The infant has received only the first DTaP dose. At home there is also a 4-week-old cousin, and the mother's sister, who is 30 weeks pregnant, visits daily. [4]

Question: Outline the immediate and stepwise management of this infant and the public-health response to protect the household, including the diagnosis, treatment, infection control, contact prophylaxis and prevention. (10 marks) [4]

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, with a low threshold for PICU involvement if apnoea or cyanosis recurs. Apnoea can be the first and lethal sign in this age group. [4]

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 cough contact and the infant's apnoea make the clinical diagnosis likely while PCR is pending; do not delay management while waiting for the result. [4]

Treatment and supportive care (2 marks). Start a macrolide — azithromycin first-line, given over five days — principally to limit the infectious period and protect contacts; it rarely shortens the paroxysmal course once established. In a neonate, azithromycin is preferred over erythromycin because of the infantile-hypertrophic-pyloric-stenosis risk. Provide supportive care: supplemental oxygen for desaturation, gentle suctioning, minimal stimulation to avoid triggering paroxysms, and feed and hydration support. [4]

Infection control and notification (2 marks). Isolate with droplet precautions and exclude until five days of effective antibiotic. Notify public health — pertussis is notifiable — because notification triggers the contact-tracing and prophylaxis response that protects the household's vulnerable contacts. [4] [6]

Contact prophylaxis and prevention (2 marks). Trace the household and close contacts and prioritise the high-risk contacts for prompt macrolide prophylaxis: the 4-week-old cousin (another infant under six months), the mother's sister who is 30 weeks pregnant, and any unvaccinated contact. Give catch-up vaccination to under-immunised contacts, and reinforce that maternal Tdap in every pregnancy protects the next infant from the first weeks of life. The household is the unit of prevention: closing the transmission chain around the infant is what stops the next apnoeic baby. [4] [6]