# Pertussis > Pertussis for FMGE Paediatrics: catarrhal to paroxysmal stages, whoop and post-tussive vomiting, absolute lymphocytosis, macrolides and vaccine choices. - Canonical URL: https://prepelephant.com/topics/fmge/paediatrics/pertussis-fmge - Exam / course: FMGE · Subject: Paediatrics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Pertussis", PrepElephant, https://prepelephant.com/topics/fmge/paediatrics/pertussis-fmge ## Direct answer Coughing in bursts for three weeks — runs of ten to twenty rapid coughs ending in a whoop and then vomiting, in a child who looks well between spells — is pertussis until excluded, and the paroxysms follow a catarrhal week that was the most infectious stage of all. Bordetella pertussis causes the whooping cough of the unimmunised; the laboratory signature is absolute lymphocytosis, and treatment is azithromycin, the macrolide also chosen for neonates because erythromycin is linked to infantile hypertrophic pyloric stenosis. The disease kills infants under six months, who often never whoop: they present with apnoea. ## What you must remember - The three stages: catarrhal (one to two weeks of ordinary coryza — maximal infectiousness, least suspicion), paroxysmal (two to six weeks of whooping, cyanosis and post-tussive vomiting), convalescent (fading over weeks to months) — the hundred-day cough. - The paroxysm: an inspiratory whoop closes a run of rapid coughs; whoops need strength to force inspiration, so they are absent in young infants, in whom apnoea, bradycardia or gagging may be the only sign. - Laboratory: absolute lymphocytosis, often 20,000–50,000 per microlitre with lymphocyte predominance, is the classic clue; culture on Regan-Lowe or Bordet-Gengou medium is most sensitive catarrally, PCR extends detection later. - Treatment: azithromycin for five days, first-line at every age including the neonatal period; clarithromycin or 14 days of erythromycin in older infants, with trimethoprim-sulfamethoxazole as second-line. - Timing of benefit: antibiotics in the catarrhal or early paroxysmal phase shorten the illness; later they mainly stop transmission — the point that tests understanding rather than memory. - Prophylaxis: a macrolide for household and close contacts, especially infants and pregnant women, ideally within 21 days of exposure. - Complications: pneumonia (the commonest cause of death), apnoea and seizures in young infants, hypoxic encephalopathy, subconjunctival haemorrhages, torn frenulum, hernias and rib fractures. - Vaccines: the whole-cell DTwP of India's programme, more reactogenic but strongly immunogenic, versus the acellular DTaP of the IAP schedule; maternal Tdap at 27–36 weeks protects newborns by passive antibody; immunity wanes, sustaining adolescent and adult disease that reinfects infants. ## The infant who never whoops A six-week-old, just short of his first vaccine visit, is brought for episodes of "stopping breathing" after feeds; the mother and a school-going sibling have coughed for three weeks. In the cot he feeds, falls into a run of coughs, reddens, and has a five-second apnoea with desaturation. White count 34,000 with 70 per cent lymphocytes. This is pertussis in its most dangerous costume: admission for monitoring, oxygen and suction as needed, azithromycin for five days, and the same drug for mother, sibling and household simultaneously. Small frequent feeds, re-fed after vomiting, are the practical half of management. The vignette carries the tested points in one line: apnoea without whoop in a neonate, lymphocytosis, the family cough, and prophylaxis of contacts rather than treatment of the patient alone. A vaccinated four-year-old with a lingering nocturnal cough for six weeks is still pertussis — waned immunity — but the management is macrolide and reassurance, not admission. ## Where students slip Hunting the whoop in young infants, in whom its absence is a feature rather than a counter-argument — apnoea, cyanosis and post-prandial gagging are their language. Expecting the antibiotic to cure the cough of established paroxysmal disease: late therapy ends contagiousness, the cough runs its course, and parents' disappointment becomes a compliance problem unless explained in advance. Misreading the count: a high white count with lymphocyte predominance in a coughing child is pertussis until disproved, not leukaemia — which brings blasts and other cytopenias. And the pharmacology favourite: erythromycin's pyloric-stenosis association in neonates, which is why azithromycin is preferred under one month. ## Frequently asked questions ### Which stage of pertussis is most infectious? The catarrhal stage, when the illness looks like an ordinary cold — one to two weeks of coryza that raises the least suspicion while bacterial shedding is maximal. ### Why is the whoop absent in young infants? They cannot generate the forceful inspiration against a narrowed glottis; instead they show apnoea, cyanosis or exhaustion after feeds, which is more dangerous than the whoop. ### What laboratory finding is classical in pertussis? Absolute lymphocytosis, frequently 20,000–50,000 cells per microlitre, predominantly small lymphocytes, in a child with paroxysmal cough. ### Which antibiotic is preferred in neonatal pertussis? Azithromycin for five days, because erythromycin in the first weeks of life is associated with infantile hypertrophic pyloric stenosis. ### Do antibiotics help if given late? They shorten the illness mainly in the catarrhal and early paroxysmal stages; later they clear the organism and prevent spread rather than aborting the cough. ### How is the newborn best protected before vaccination? By maternal Tdap at 27–36 weeks of pregnancy, which transfers antibody, alongside cocooning — treating and immunising household contacts.