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Pertussis (whooping cough)
Pertussis is a Bordetella pertussis infection that in a young infant appears as apnoea and cyanosis without a whoop, and in an older child as a long paroxysmal cough; treatment and household prophylaxis use azithromycin, and the main protection of the infant is maternal vaccination in pregnancy.
Why it matters in the exam
The classic question describes a 6-week-old infant with coughing spells, cyanosis and apnoea, a blood count with marked leucocytosis and lymphocytosis, and asks for the diagnosis, how to confirm it and what to give. Another question asks who needs prophylaxis — the answer is all household members and close contacts, regardless of their vaccination status.
There are three stages: catarrhal (1–2 weeks, looks like a cold and is the most contagious), paroxysmal (2–6 weeks, coughing fits, an inspiratory whoop and post-tussive vomiting) and convalescent (weeks to months). Diagnosis is by nasopharyngeal PCR in the first three weeks; later, PCR and culture are less sensitive. Antibiotics in the paroxysmal stage do not shorten the cough but stop transmission.
Under one month of age azithromycin is the preferred drug, because erythromycin is linked to infantile hypertrophic pyloric stenosis. Extreme leucocytosis in a young infant is associated with pulmonary hypertension and death. In Israel Tdap is given in every pregnancy, and the childhood schedule includes doses at 2, 4 and 6 months, a booster at one year and boosters in the second and eighth school grades — immunity wanes, so vaccinated adolescents and adults still infect infants.
Key points
- In the infant: apnoea and cyanosis; in the older child: paroxysmal cough with a whoop.
- Marked lymphocytosis is a key laboratory clue.
- Diagnosis by nasopharyngeal PCR in the first three weeks.
- Azithromycin for treatment and for prophylaxis of all household members.
- Tdap in every pregnancy protects the infant in the first months.
Summary table
| Topic | What to remember | Numbers | Exam meaning |
|---|---|---|---|
| Infant under 6 months | Apnoea, cyanosis, no whoop | Leucocytosis with lymphocytosis | Usually admitted; highest mortality |
| Older child and adolescent | Paroxysmal cough, whoop, post-tussive vomiting | Cough for more than two weeks | The "hundred-day cough" |
| Diagnosis | Nasopharyngeal PCR | Most sensitive in the first 3 weeks | Serology only later |
| Treatment and household prophylaxis | Azithromycin | Under 6 months 10 mg/kg per day for 5 days; over 6 months 10 mg/kg on day 1 and 5 mg/kg on days 2–5 | The same regimen for treatment and prophylaxis |
| Alternative | TMP-SMX | Only over 2 months of age | Erythromycin avoided under one month |
| Prevention | Tdap in every pregnancy; vaccination by the Ministry of Health schedule | Doses at 2, 4, 6 months, booster at one year, second and eighth grade | Maternal antibodies protect the infant in the first months |
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Sources
- AAP Red Book: Report of the Committee on Infectious Diseases, 2024–2027 — Pertussis (Whooping Cough)
- CDC Recommended Antimicrobial Agents for the Treatment and Postexposure Prophylaxis of Pertussis, 2005 (current CDC guidance) — Treatment and prophylaxis by age group
- Israeli Ministry of Health, routine childhood vaccination schedule (current) — DTaP-containing vaccines and Tdap in pregnancy
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Pertussis (Bordetella pertussis and Bordetella parapertussis)
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.