Whooping cough

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Bordetella pertussis spreads in respiratory droplets and is highly infectious during the catarrhal and early cough phase. Household transmission is especially important for newborn exposure.

After an incubation commonly around 7–10 days, mild coryza and cough progress over 1–2 weeks to paroxysms. A forceful inspiratory effort against a narrowed glottis creates the whoop, but it is not universal.

Pertussis toxin and other bacterial factors injure ciliated epithelium and disrupt clearance. Cough persists after bacterial burden falls because epithelial injury and neural hypersensitivity recover slowly.

The youngest infants have immature respiratory control and little vaccine-derived protection. They can develop apnoea, pneumonia, lymphocytosis, pulmonary vascular obstruction and encephalopathy.

Clinical history should describe cough duration, clustering, whoop, vomiting, colour change, apnoea and recovery, and ask specifically about maternal and infant vaccine dates and known cases.

PCR detects bacterial DNA and remains useful after culture sensitivity falls, but timing and sampling quality matter. A posterior nasopharyngeal sample is required; a superficial nasal swab can be falsely negative.

Macrolide treatment primarily interrupts transmission. Early catarrhal treatment may reduce severity, but once toxin-mediated paroxysms are established, families should expect gradual recovery despite bacterial eradication.

Supportive infant care includes apnoea monitoring, gentle suction only when needed, small safe feeds or enteral support and minimal stimulation that can trigger paroxysms. Cough medicines are ineffective and potentially harmful.

Notification enables identification of vulnerable contacts, targeted prophylaxis and outbreak management. Public-health advice may change during periods of increased activity, so current national guidance is authoritative.

Vaccination reduces severe disease but immunity wanes and infection can occur after vaccination. A vaccinated child with compatible prolonged paroxysmal cough can still have pertussis.

Caregivers should know that infectiousness falls after 48 hours of appropriate antibiotic, but cough can continue for weeks and does not mean ongoing treatment failure.

Pregnancy vaccination transfers antibody before birth. It is repeated in every pregnancy because protection of the next infant depends on current maternal antibody.

Key points

Pertussis begins with a catarrhal phase resembling a cold, then develops paroxysms of repeated cough, inspiratory whoop, post-tussive vomiting and exhaustion; cough commonly lasts 6–8 weeks or longer.
Infants may present with apnoea, cyanosis, poor feeding or bradycardia and no whoop. Adolescents and vaccinated children may have prolonged nonspecific cough.
Suspect pertussis with cough lasting 2 weeks or more plus paroxysms, whoop or post-tussive vomiting, or earlier when epidemiology or infant apnoea is compatible.
First-line confirmation early in illness is a properly obtained nasopharyngeal sample for PCR according to age and time since cough onset. Culture has highest specificity but sensitivity falls after antibiotics and time.
UKHSA testing changes with age and duration; later illness may use oral-fluid antibody or serology in defined age groups. Follow the current testing algorithm rather than sending every modality.
Pertussis is notifiable on clinical suspicion in England; do not wait for laboratory confirmation before notification or action around a vulnerable infant.
Offer an appropriate macrolide within 21 days of cough onset to eradicate carriage and reduce transmission. Antibiotics given after the paroxysmal phase begins often do not shorten the cough.
Current UKHSA regimens include clarithromycin 7.5 mg/kg twice daily for 7 days in neonates and children under 8 kg; weight-banded doses apply above 8 kg. Verify the current BNF-C and UKHSA table.
Azithromycin 10 mg/kg once daily for 3 days is an alternative from infancy, maximum 500 mg above 6 months; macrolides require interaction and QT-risk review.
Exclude from school, childcare or communal residential areas until 48 hours after appropriate antibiotics begin, or 21 days from cough onset if untreated.
Health protection, not the individual prescriber alone, determines chemoprophylaxis and vaccination for eligible close contacts according to exposure timing and vulnerability.
Prevent severe infant disease through maternal pertussis vaccination in every pregnancy, normally around 20 weeks and ideally before 32 weeks, plus on-time infant vaccines at 8, 12 and 16 weeks and later boosters.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Bordetella pertussis infection

A toxin-producing Gram-negative coccobacillus spreads through close respiratory-droplet exposure and attaches to ciliated airway epithelium. within the child-specific clinical phenotype.

Waning protection

Vaccine and infection-derived immunity reduce severity but decline over time, allowing disease in older vaccinated children and adults.

Household exposure

Parents, siblings and other close contacts with mild prolonged cough are common sources for unprotected young infants.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Ciliary epithelial injury
Bacterial adherence and toxins damage mucociliary function, leaving retained secretions and a persistently sensitised cough reflex.
2
Paroxysmal airflow
Repeated expiratory cough empties the lungs before a forceful inspiration produces whoop, vomiting, hypoxaemia or syncope.
3
Infant apnoea
Immature respiratory control and toxin effects allow pauses and bradycardia without the forceful cough needed to generate a whoop.
4
Severe pulmonary disease
Pneumonia, extreme lymphocytosis and pulmonary vascular obstruction can produce pulmonary hypertension and refractory hypoxaemia in young infants.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Catarrhal phase

Identify initial coryza, mild fever and increasing cough during the period when contagiousness is greatest.

Paroxysmal phase

Ask about cough clusters, inspiratory whoop, post-tussive vomiting, cyanosis, exhaustion and relatively well intervals.

Infant phenotype

Look for apnoea, bradycardia, colour change, poor feeding and pneumonia even when cough and whoop are absent.

Exposure and vaccination

Record known cases, household cough, school outbreak and exact maternal, infant and booster vaccine dates.

Severity

Measure oxygenation, hydration, respiratory effort and weight and assess seizures, consciousness and recovery between episodes.

Public-health context

Establish cough-onset date, childcare attendance and vulnerable close contacts because these determine testing, exclusion and prophylaxis windows.

Red flags requiring action

Any apnoea, cyanosis, bradycardia, seizure, reduced consciousness or exhaustion in an infant requires urgent hospital assessment.
Age under 6 months carries the greatest morbidity and mortality; absence of a whoop does not reduce risk.
Poor feeding, repeated post-tussive vomiting, dehydration or weight loss may require admission and feeding support.
Tachycardia, marked tachypnoea, hypoxaemia, pneumonia or a very high lymphocyte count can accompany severe infant pertussis and pulmonary hypertension.
Haemoptysis, focal neurology, persistent fever or focal chest signs requires evaluation for complications or an alternative diagnosis.
A suspected case with household contact with a pregnant person or incompletely vaccinated infant needs prompt health-protection risk assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line: age- and time-directed pertussis testingFirst stepFirst line
Why
Confirm infection using the current UKHSA algorithm without delaying notification.
Interpretation and limitations
Choose PCR, culture, oral fluid or serology by age and cough duration; a negative late or poorly collected sample does not fully exclude disease.
02
Nasopharyngeal PCR
Why
Detect Bordetella DNA during early weeks of cough when organism remains in the airway.
Interpretation and limitations
A positive compatible result supports diagnosis; collect a true posterior nasopharyngeal sample and record antibiotic exposure.
03
Culture
Why
Provide highly specific confirmation and an isolate for public-health purposes early in illness.
Interpretation and limitations
Sensitivity falls with duration and macrolide treatment, so a negative culture cannot exclude clinical pertussis.
04
Full blood count in a sick infant
Why
Identify marked lymphocytosis associated with severe infant disease and support broader assessment.
Interpretation and limitations
Hyperleucocytosis is a severity marker rather than a standalone diagnostic test and prompts intensive senior review.
05
Chest imaging and cardiorespiratory tests
Why
Assess pneumonia, collapse, pulmonary hypertension or another diagnosis in severe illness.
Interpretation and limitations
Imaging is not required for uncomplicated outpatient cough; echocardiography and intensive monitoring are specialist decisions.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Viral respiratory infection

RSV, influenza and other viruses cause cough and apnoea but lack the classic prolonged paroxysmal trajectory or exposure pattern.

Asthma or post-viral cough

Episodic wheeze, triggers and bronchodilator response favour asthma, while post-viral cough usually lacks whoop and vomiting paroxysms.

Foreign-body aspiration

Abrupt choking, focal air entry and no catarrhal evolution suggests an inhaled object requiring bronchoscopy assessment.

Pneumonia

Persistent fever, focal crackles, hypoxaemia between paroxysms and consolidation may indicate primary or secondary pneumonia. when timing, examination and trajectory are integrated.

Reflux or aspiration

Feed-related cough, choking, wet breathing and recurrent chest signs supports swallowing dysfunction rather than pertussis alone.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SuspectNotify and test promptlyFirst stepA compatible cough or infant apnoea syndrome is identified.

1Assess age-specific severity and admit young or physiologically compromised infants.
2Notify on clinical suspicion and collect the test recommended for age and cough duration.
3Record cough onset and vulnerable contacts and begin infection-control measures without awaiting the result.

02TreatEradicate within 21 daysA suspected, linked or confirmed case is within 21 days of cough onset.

1Select clarithromycin or azithromycin using the current UKHSA and BNF-C age and weight regimen.
2Review QT risk, interactions, hepatic disease and macrolide adverse effects, especially in neonates.
3Explain that transmission falls after 48 hours but cough often continues despite successful treatment.

03ProtectCoordinate contacts and exclusionThe case attends a setting or has close contact with a vulnerable person.

1Exclude until 48 hours of appropriate antibiotic are complete or 21 days from cough onset if untreated.
2Contact the health protection team for risk-based prophylaxis and vaccination of eligible close contacts.
3Ensure infant and pregnancy vaccination is offered or caught up without using antibiotics as a vaccine substitute.

04SevereSupport the young infantApnoea, cyanosis, feeding failure, pneumonia or exhaustion is present.

1Admit for cardiorespiratory monitoring, oxygen and ventilation support as needed.
2Provide safe small feeds, enteral or intravenous hydration and minimise paroxysm triggers.
3Involve paediatric intensive care early for recurrent apnoea, hyperleucocytosis, pulmonary hypertension or worsening gas exchange.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Preferred short-course macrolide in current UKHSA age and weight regimens for eradication and transmission control.

Clarithromycin

Neonate and child under 8 kg: 7.5 mg/kg orally twice daily for 7 days. At 8 kg and above use the current UKHSA weight bands; age 12–17 years: 500 mg twice daily for 7 days.

Verify BNF-C and UKHSA guidance, weight and formulation. Review QT prolongation, interacting medicines, hepatic impairment and gastrointestinal effects; macrolides require particular caution in neonates.

Alternative macrolide treatment or chemoprophylaxis that provides a shorter eradication course.

Azithromycin

Neonate and infant: 10 mg/kg orally once daily for 3 days; after 6 months use 10 mg/kg once daily, maximum 500 mg, for 3 days.

Check current national regimen, QT risk, liver disease and interactions. Counsel caregivers of young infants about persistent projectile vomiting because macrolide exposure has been associated with hypertrophic pyloric stenosis.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Apnoea and respiratory failure

Infants may need ventilatory support for recurrent pauses, exhaustion, pneumonia or pulmonary hypertension. when recognition or effective treatment is delayed.

Neurological injury

Hypoxaemia, intracranial bleeding from pressure surges or toxin-associated encephalopathy can cause seizures and lasting impairment. when recognition or effective treatment is delayed.

Feeding and growth failure

Post-tussive vomiting and exhausting paroxysms reduce intake, causing dehydration and weight loss over weeks. when recognition or effective treatment is delayed.

Mechanical cough injury

Forceful prolonged coughing can cause subconjunctival haemorrhage, epistaxis, hernia, rib pain or urinary incontinence. when recognition or effective treatment is delayed.

Transmission to vulnerable contacts

Delayed diagnosis exposes incompletely vaccinated infants and pregnant household members before exclusion or prophylaxis is arranged.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Monitor infants for apnoea, bradycardia, cyanosis and recovery between paroxysms, including during sleep and feeds.
Track intake, post-tussive vomiting, wet nappies and weight during the prolonged cough period.
Review respiratory effort, oxygenation and fever for secondary pneumonia or deterioration.
Confirm completion of 48 hours of appropriate antibiotic before return to a communal setting.
Check contact action and vaccination with the health protection team, especially around an infant under 1 year.
Review macrolide tolerance, interactions and signs of pyloric stenosis in a treated young infant.
Explain gradual recovery and reassess if cough, fever or function worsens rather than simply persists.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The infant may not whoop

Apnoea and colour change can be the dominant presentation because a young infant cannot generate the classic forceful inspiratory sound.

Treatment and symptom relief differ

Macrolides clear carriage and protect contacts, but established toxin-mediated coughing can continue for many weeks.

Cough onset starts the clock

Testing, the 21-day treatment window and untreated exclusion all depend on a carefully established onset date.

Vaccination modifies rather than excludes

Immunised older children can still develop a milder prolonged cough and transmit infection to vulnerable infants.

Notification precedes proof

Public-health protection should begin from a compatible clinical suspicion, not after a delayed laboratory result.

11Common pitfallsFrequent interpretation and management errors.

01
Do not require a whoop before suspecting pertussis in an infant.
02
Do not wait for PCR confirmation before notification and vulnerable-contact action.
03
Do not promise that antibiotics will stop an established cough.
04
Do not use a superficial nasal swab when a nasopharyngeal sample is required.
05
Do not return a child to school before 48 hours of appropriate antibiotic.
06
Do not prescribe contact prophylaxis without applying current UKHSA eligibility.
07
Do not overlook QT interactions or neonatal macrolide-associated pyloric-stenosis risk.
08
Do not miss routine infant or pregnancy vaccination while managing an acute case.