Pertussis

Overview

Pertussis, also known as whooping cough, is an acute bacterial infection of the respiratory tract caused by Bordetella pertussis. It classically presents with paroxysms of cough and a whooping sound on inspiration.

Disease epidemiology

Pertussis occurs worldwide with outbreaks occurring every 3 to 4 years. In Singapore, pertussis vaccination is part of the National Childhood Immunisation Programme. Increasing incidence in adolescents and adults (with occasional community and school outbreaks) is noted and likely due to waning immunity. Adolescents and adults with unrecognised pertussis are a reservoir of infection for infants and children. Humans are the only known reservoir.

Pathogen(s)

Bordetella pertussis

Transmission

Pertussis primarily transmits through direct deposition of infectious respiratory particles (IRPs) such as when an infected person coughs or sneezes. It can also spread via contact with contaminated surfaces such as when IRPs settle on surfaces or transfer through contact (e.g. handshake) before reaching the mouth, nose or eyes.

Incubation period: Typically 9 to 10 days; ranging from 6 to 20 days.

Infectious period: Infectious for about 3 weeks, from the catarrhal stage (about 1 week) through the paroxysmal cough stage (about 2 weeks) in an untreated patient. If antibiotics are initiated, the period of infectiousness is usually ≤5 days after onset of treatment.

Clinical features

The disease can occur in both children and adults. All persons who have not been immunised are susceptible, and pertussis can be severe in immune-naïve individuals of any age.

In unvaccinated children, the classic presentation has 3 stages:

1. Catarrhal stage (1 to 2 weeks): Similar to an upper respiratory tract infection with coryza and mild cough symptoms. Fever is often absent.

2. Paroxysmal stage (2 to 6 weeks): Increased cough with spells of repetitive dry cough, followed by sudden inspiratory effort (whoop) and post-tussive emesis.

3. Convalescent stage (more than 2 weeks): Decreasing frequency and severity of coughing episodes. Average duration of cough is approximately 50 days.

Infants younger than 6 months may have cough without a typical whoop and may have apnoea/respiratory distress. Adolescents and adults can have a prominent hacking cough that lacks the characteristic whoop. Prior immunisation can lead to atypical presentations.

Risk factors

All persons who are unvaccinated or partially vaccinated.

Diagnosis

Detection of B. pertussis in respiratory samples including nasal, nasopharyngeal, throat swabs, sputum, endotracheal aspirate and bronchoalveolar lavage via Polymerase Chain Reaction (PCR) or isolation.

Treatment and management

Antibiotic treatment is unlikely to shorten the duration of illness if started more than 1 week after symptom onset, but it is beneficial in shortening the infectious period and decreasing transmission. Macrolides are the recommended first line of therapy.

Infection in infants under age 6 months may require hospitalisation due to complication of hypoxaemia, apnoea, or poor feeding.

Precaution, prevention, and control

Isolation measures

Patients should be isolated. Suspect and confirmed cases should be removed from the presence of young children and non-immunised infants until patients have received at least 5 days of antibiotics.

In healthcare settings, standard and droplet precaution should be applied until 5 days after initiation of effective antibiotic therapy.

Contact management

Post-exposure chemoprophylaxis is recommended for household contacts (regardless of immunisation status) and contacts who are personally at high risk of developing severe disease (e.g. children below 1 year) or are in close contact with those at high risk of severe disease (e.g. pregnant women in their third trimester who may be a source of pertussis to their neonates) within 3 weeks of exposure.

There is limited evidence for post-exposure vaccination, however contacts are advised to keep up to date with their vaccinations to protect against future exposure.

Vaccination

Vaccination is the most effective preventive measure.

The National Childhood Immunisation Schedule recommends:

• 3 doses of DTaP (diphtheria and tetanus toxoids and acellular pertussis vaccine) at 2 months, 4 months and 6 months of age;

• 1 booster dose of DTaP at 18 months of age; and

• 1 booster dose of Tdap (Tetanus- diphtheria- acellular pertussis) at 10 to 11 years of age.

The National Adult Immunisation Schedule recommends:

• Tdap vaccine for adults with certain medical conditions, with no history of previous vaccination or if their last vaccination was at least 10 years ago; and

• One dose of Tdap vaccination for pregnant women during 16 to 32 weeks of each pregnancy for protection of the infant against pertussis, regardless of the interval since the previous Tdap vaccination.

Notification

Pertussis is a legally notifiable disease in Singapore.

Who should notify:

• Laboratories

When to notify:

• On laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information. 

Notification timeline:

• As soon as possible. No later than 72 hours.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of pertussis cases in Singapore.

For more information on pertussis, please refer to the World Health Organization website.

For general travel advisory, please refer to Health Advice for Travellers.