What is pertussis and who is at risk?
Pertussis (whooping cough) is a highly contagious respiratory disease caused by *Bordetella pertussis*, a fastidious, aerobic, gram-negative coccobacillus that infects the ciliated epithelium of the respiratory tract. Humans are the only known reservoir — there is no animal or insect source. Spread is by respiratory droplets through close contact. The incubation period is usually 5 to 10 days, but can be as long as 21 days.
Other Bordetella species also cause human illness: *B. parapertussis* (a usually milder pertussis-like illness), B. bronchiseptica and B. holmesii. Pertussis has been recognised since the 1500s; the Mandarin Chinese name means 'hundred-day cough' because of its long course.
Infants younger than 6 months carry the highest risk of severe disease, hospitalisation and death. Adolescents and adults often have a milder, atypical illness — a prolonged cough without the whoop — which delays diagnosis and lets them transmit infection to infants. Immunity after infection or vaccination is not lifelong (infection gives protection for roughly 4 to 20 years).
How does Bordetella pertussis cause disease?
The bacteria stay on the mucosal surface and usually do not invade the bloodstream. They attach to ciliated cells, multiply, paralyse mucociliary clearance and damage the epithelium. The toxins explain most exam questions.
| Factor | Role |
|---|---|
| Filamentous haemagglutinin (FHA) | Adhesin for ciliated epithelium; also agglutinates red cells |
| Pertactin | Adhesin; helps protect the organism from neutrophil-mediated clearance |
| Fimbriae | Adhesion |
| Pertussis toxin (main virulence factor) | Inactivates G proteins → disrupts host signalling; blocks lymphocyte extravasation and releases them from lymphoid tissue → marked lymphocytosis |
| Adenylate cyclase toxin | Raises cAMP in phagocytes → impairs neutrophil and macrophage function |
| Tracheal cytotoxin | Damages ciliated cells, impairing mucociliary clearance |
| Endotoxin (lipooligosaccharide) and dermonecrotic toxin | Local inflammation and tissue damage |
The characteristic paroxysmal cough arises from airway irritation by mucus and damaged epithelium combined with a hyper-responsive cough reflex. The inspiratory whoop is produced when air is rapidly inhaled through a partly closed glottis at the end of a coughing fit, and increased intrathoracic pressure triggers post-tussive vomiting.
What are the clinical stages of pertussis?
| Stage | Features | Duration (approximate) |
|---|---|---|
| 1. Catarrhal | Coryza, low-grade fever, mild occasional cough that gradually worsens; apnoea in infants | 1–2 weeks |
| 2. Paroxysmal | Paroxysms of numerous rapid coughs, long inspiratory effort with a high-pitched whoop, cyanosis, exhaustion, post-tussive vomiting; attacks worse at night, average about 15 per 24 hours | Attacks increase over the first 1–2 weeks, plateau for 2–3 weeks, then decline |
| 3. Convalescent | Gradual recovery; less persistent coughs that disappear in 2–3 weeks; paroxysms may recur with later respiratory infections for months | Weeks to months |
Case definitions. The CDC clinical case definition is a cough of any duration with at least one of paroxysmal coughing, inspiratory whoop, post-tussive emesis or apnoea in contact with a confirmed case, or a cough of at least 2 weeks with at least one of these features. The WHO definition used in India's immunisation handbook is a cough lasting at least 2 weeks with paroxysms, inspiratory whooping or post-tussive vomiting and no other apparent cause.
How is pertussis diagnosed?
Specimens come from the nasopharynx (swab or aspirate). The best test depends on how long the patient has been coughing.
| Test | Points |
|---|---|
| PCR | Confirmatory test of choice; rapid; sensitivity 77–97% and specificity 88–97% within 1 to 4 weeks of onset |
| Culture | Needs special media — Bordet-Gengou (blood-containing) or Regan-Lowe (charcoal-based) agar; slow, 7 to 10 days; most sensitive in catarrhal phase and first 2 weeks of cough |
| Serology | Useful late (3 to 12 weeks after onset); not for infants under 6 months or the recently vaccinated |
| Direct fluorescent antibody | No longer recommended — low sensitivity and specificity |
| Complete blood count | Leukocytosis with absolute lymphocytosis; in infants under 3 months, WBC >20,000/µL with >50% lymphocytes is highly suggestive |
How is pertussis treated and how is spread prevented?
- First-line: a macrolide. Azithromycin is preferred for tolerability and simple dosing; alternatives are clarithromycin and erythromycin.
- Avoid erythromycin in young infants — it is associated with infantile hypertrophic pyloric stenosis.
- Co-trimoxazole (trimethoprim-sulfamethoxazole) is the alternative for patients who cannot take macrolides and are older than 2 months.
- Timing: treat early — ideally in the first 1 to 2 weeks before paroxysms. Treatment is recommended up to 3 weeks after cough onset mainly to reduce transmission, since antibiotics have little effect on symptoms once the paroxysmal phase is established.
- Isolation: droplet precautions; patients are non-infectious after 5 days of appropriate antibiotics, otherwise infectious for up to 3 weeks after cough onset.
- Post-exposure prophylaxis: all household contacts, high-risk people (infants under 12 months, pregnant women, immunocompromised) and those in close contact with high-risk people — with the same macrolide regimens, ideally within 21 days of cough onset in the index case.
Supportive care is the mainstay, particularly in infants under 6 months, who often need admission for apnoea, hypoxia, dehydration and pneumonia — monitoring, hydration, nutrition and respiratory support. In severe infant disease with extreme leukocytosis, pulmonary hypertension or shock, exchange transfusion may be considered, and ECMO may be needed for refractory respiratory failure. Corticosteroids, bronchodilators, antihistamines and cough suppressants have not shown consistent benefit and are not routinely recommended.
What is the DPT vaccine and what is India's schedule?
DPT (DwPT) combines diphtheria and tetanus toxoids with whole-cell pertussis vaccine. India's pentavalent vaccine contains five antigens — diphtheria, pertussis, tetanus, hepatitis B and Haemophilus influenzae type b — and reduced the number of injections in the first year of life from ten to seven (not counting IPV). Pentavalent has to be given only after a child is 6 weeks old.
| Age | Vaccine | Dose / route / site |
|---|---|---|
| 6, 10 and 14 weeks | Pentavalent 1, 2, 3 | 0.5 mL intramuscular, left anterolateral mid-thigh; can be started up to 1 year of age; no booster of pentavalent |
| 16–24 months | DPT booster-1 | 0.5 mL IM, anterolateral mid-thigh (left); maximum age 7 years |
| 5–6 years | DPT booster-2 | 0.5 mL IM, upper arm; maximum age 7 years |
- A child whose series was started with DPT and hepatitis B continues with those vaccines, not pentavalent.
- Unvaccinated child aged 5–7 years: give DPT 1, 2 and 3 at 1-month intervals, then a booster at least 6 months after DPT-3, up to age 7 years.
- Pentavalent must not be given below 6 weeks of age, or to a child who had a severe reaction to a previous dose.
- The VVM on DPT corresponds to the pertussis component of the vaccine — it is the heat-sensitive part. DPT and pentavalent are freeze-sensitive (DPT freezes at about −3°C) and must never be frozen.
- Give injections in the anterolateral mid-thigh, not the gluteal region, to avoid sciatic nerve damage and a poor immune response.
The full schedule, including the adolescent tetanus–diphtheria booster, is on the national immunisation schedule page; see also tetanus for the T component, and measles, rubella and varicella for other childhood infections.
What are the adverse events of DPT, and what about pregnancy?
| Type of reaction | Details |
|---|---|
| Common, minor | Local reaction (pain, swelling, redness) up to 50%; fever (over 38°C) up to 50%; systemic symptoms such as irritability up to 55% |
| Persistent inconsolable screaming | Crying lasting 3 hours or longer with high-pitched screaming; onset within 24 hours; settles within a day |
| Seizures | Within 0–3 days; mostly febrile; self-limiting; paracetamol and cooling |
| Hypotonic-hyporesponsive episode (HHE) | Within 0–48 hours |
| Anaphylaxis | Within 0–1 hour |
| Encephalopathy | Listed as a very rare possible reaction, but it is not certain that the vaccine causes it |
Pertussis in pregnancy. Newborns are protected only by maternal antibodies, so the CDC recommends one dose of Tdap in every pregnancy, preferably early in weeks 27 to 36. StatPearls notes that the older 'cocooning' strategy (vaccinating close contacts) is no longer routinely recommended, because vaccinated contacts can still acquire and transmit pertussis. The US schedule gives DTaP (acellular) to children under 7 years in 5 doses (2, 4, 6 and 15–18 months, and 4–6 years) and Tdap to adolescents at 11–12 years — compare with India's whole-cell schedule above.
What are the high-yield exam points?
- Organism: *B. pertussis* — gram-negative coccobacillus; culture on Bordet-Gengou / Regan-Lowe (charcoal).
- Main virulence factor: pertussis toxin (inactivates G proteins) → lymphocytosis; adenylate cyclase toxin ↑ cAMP; tracheal cytotoxin damages cilia.
- Stages: catarrhal → paroxysmal (whoop, post-tussive vomiting) → convalescent.
- Best confirmatory test: PCR on nasopharyngeal specimen; culture takes 7–10 days.
- Treatment: azithromycin (macrolide); avoid erythromycin in neonates (pyloric stenosis); co-trimoxazole if over 2 months and macrolide-intolerant.
- India: pentavalent at 6, 10, 14 weeks; DPT boosters at 16–24 months and 5–6 years; DPT maximum age 7 years.
- VVM on DPT corresponds to the pertussis component.
- Pregnancy: Tdap each pregnancy, weeks 27–36 (CDC).