Pertussis

What is it?

Pertussis (whooping cough) is a highly contagious, respiratory disease caused by an infection with the bacterium Bordetella pertussis. The bacteria attach to the cilia (tiny, hair-like structures) that line the upper respiratory system. The bacteria release toxins, which damage the cilia and cause airways to swell. Pertussis infection is usually more serious in infants under 6 months, but it can affect people of any age.

What to look for

Symptoms begin 6 to 20 days after exposure and initially include rhinorrhoea (runny nose), malaise and a non-specific cough (the catarrhal phase). Approximately one week later, periods of coughing increase with intensity (the paroxysmal phase). A characteristic deep gasp (or “whoop”) may be heard on inspiration, but this is not present in all infections.

During or just following an episode of paroxysmal coughing, babies may have a period of apnoea where they stop breathing for a short period. This may be associated with some colour changes where their skin may appear blue or dusky, especially around the mouth.

Complications of pertussis in infants can include vomiting and difficulty feeding due to prolonged paroxysmal coughing episodes. Rare complications of pertussis in infants include pneumonia and encephalitis, which can be fatal. Complications in older children and adults can include fainting episodes, sleeplessness and rib fractures due to paroxysmal coughing episodes.

How is it transmitted?

Transmission of pertussis is through the inhalation of infected respiratory secretions that have been made airborne by coughing, sneezing and speaking. Pertussis is highly contagious, with one infected individual likely to transmit infection to 70–100% of their household members. Some people with mild symptoms of pertussis may be unaware they are infected, but can still spread the bacteria to others. Humans are the only known reservoir for pertussis.

The incubation period is 1 to 3 weeks. Without treatment, people with pertussis are considered infectious just prior to symptom onset and for 21 days thereafter. The infectious period is reduced to 5 days if a course of targeted antibiotics is completed.

Epidemiology

Australia has historically experienced pertussis epidemics every 3 to 4 years. There is a seasonal pattern to pertussis infections with most cases reported in the spring and summer months.

Infants under 6 months of age have the highest rates of hospitalisation and death from pertussis infection. Aboriginal and Torres Strait Islander children under 5 years have higher rates of pertussis infection and hospitalisation compared with non-Indigenous children of the same age.

With the introduction of the maternal pertussis vaccination program in 2015, there has been a significant reduction in young infants infected with pertussis and a substantial reduction in both morbidity and mortality associated with infection. In Australia, the incidence of pertussis infections in all age groups has continued to decline. Between 2016 and 2018, infants under 2 months of age had the lowest incidence of disease, and children aged 9 to 11 years had the highest incidence of disease.

Prevention

Vaccination against Bordetella pertussis is the most effective public health measure for the prevention of pertussis for both vaccine recipients (direct effect), and among unimmunised populations (indirect ‘herd’ effect).  Vaccination of pregnant people also provides short-term, passive protection to infants through the transplacental transfer of antibodies.

Pertussis vaccination is only available in Australia in combination with diphtheria and tetanus. Vaccines may also include protection against poliomyelitis, hepatitis B and haemophilus influenzae type B.

The pertussis vaccines available in Australia are acellular, meaning they are made using pertussis toxin and/or components of pertussis bacterium. In contrast, whole-cell pertussis vaccines are first generation pertussis vaccines that are made using an entire bacterium that has been inactivated. While whole cell pertussis vaccines are still available internationally, they were phased out in Australia in 1997, in favour of acellular pertussis vaccines.

Primary course

As per the National Immunisation Program (NIP), a primary course of pertussis vaccination is given at 6 weeks, 4 months, and 6 months of age (Infanrix hexa/Vaxelis).

Boosters

Booster doses are scheduled to be administered at:

• 18 months (Infanrix/Tripacel)
• 4 years (Infanrix-IPV/Quadracel)
• 12 to 13 years of age/Year 7 high school program (Boostrix/Adacel)
• Pregnant people at 20–32 weeks gestation (every pregnancy, regardless of how closely spaced).

In addition, pertussis vaccination is recommended (but not funded) for:

• Parents/guardians of a baby under 6 months of age (if they have not received a dose in the last 10 years)
• Adults aged 65 years and older who have not received a pertussis-containing vaccine in the last 10 years
• Any adult who wishes to be protected against pertussis infection who has not received a dose in the last 10 years (including healthcare workers, travellers, and early childhood educators and carers).

Grey shaded boxes – Not routinely recommended for use in this age group.
* ATAGI recommends the use of Infanrix hexa and Vaxelis in children aged < 10 years. However, the Royal Children’s Hospital (RCH) preferentially uses them up to < 18 years in instances where multiple vaccines are required (e.g. catch up, post chemotherapy/post HSCT). 

Vaccine side effects

Common side effects from pertussis vaccination include injection site reactions, fever, lethargy, headache and irritability in infants and young children. Rare side effects include allergic reaction and hypotonic-hyporesponsive episode (HHE) in infants. There has been a decrease in the incidence of HHE following the change from whole-cell pertussis to acellular pertussis vaccines on the NIP.

Resources

• Better Health Channel: Whooping cough
• Australian Immunisation Handbook: Pertussis chapter
• MVEC: Maternal Vaccination During Pregnancy
• RCH: Kids health info fact sheet
• The Immunisation Foundation of Australia
• The Raising Children Net Whooping Cough Guide
• National Notifiable Diseases Surveillance System (NNDSS)
• Australian vaccine preventable disease epidemiological review series: Pertussis, 2013-2018
• RCH: Clinical Practice Guideline Whooping cough