Pertussis (whooping cough)

Notification requirement for pertussis

Pertussis (whooping cough) is a 'routine' notifiable condition. It must be notified by medical practitioners and pathology services to the Department of Health in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services exclusions for pertussis

Children with pertussis must not go to primary school and children’s service for 21 days after the onset of cough, or until they have received 5 days of appropriate antibiotic treatment.

Unvaccinated contacts aged less than 7 years old in the same room as the case must be excluded from primary school and children's services for 14 days from the last exposure to the infectious case, or until they have received 5 days of appropriate antibiotic treatment.

For more information, see the School exclusion table.

Infectious agent of pertussis

Pertussis is caused by infection with Bordetella pertussis bacteria.

Identification of pertussis

Clinical features

Pertussis causes a respiratory illness that can vary by age. Bordetella pertussis can adhere to the cells of the respiratory tract and release toxins that cause local tissue damage which are thought to contribute to cough symptoms by disrupting mucus clearance.

The initial catarrhal stage has symptoms of coryza, cough, tiredness and sometimes a low-grade fever. These symptoms may be indistinguishable from those of a viral upper respiratory tract infection.

The subsequent paroxysmal stage usually develops after 1 to 2 weeks of illness onset and is characterised by paroxysmal coughing (intermittent, rapid coughing fits). These occur particularly at night and may cause post-tussive vomiting, cyanosis or a long inspiratory effort with a high-pitched ‘whoop’.

During the convalescent stage, cough symptoms gradually improve over several weeks. However, they may recur with subsequent respiratory tract infections for several months.

Adults and infants sometimes do not present with classical symptoms, but it is important for clinicians to have a high clinical suspicion for pertussis. Infants are less likely to have the inspiratory 'whoop' or a significant catarrhal stage, and more commonly present with apnoea, cyanosis, feeding difficulties, gasping, or choking. In adolescents and adults, pertussis may present as a non-specific protracted cough.

Vaccinated people can still contract pertussis, but their symptoms are likely to be less severe, and they are less likely to transmit the infection to others.

Complications

Complications from pertussis include pneumonia, apnoea, seizures and encephalopathy which can be potentially fatal. Infants under 6 months of age are at highest risk of these complications and death.

Other complications may include dehydration from repeated vomiting, otitis media, epistaxis as well as hernias, prolapses, pneumothorax and rib fractures from strenuous coughing.

Diagnosis

Pertussis diagnosis is suspected based on clinical assessment and confirmed on laboratory tests. Early diagnosis in people with compatible illness is important and treatment should be commenced without delay in suspected cases.

A clinical diagnosis can be confirmed by:

• detection of Bordetella pertussis by polymerase chain reaction (PCR) testing of a nasopharyngeal swab or aspirate. This is the preferred diagnostic test for pertussis in all ages. It is more sensitive in the first 3 weeks of illness but may be positive for up to 5 weeks after illness onset. Please refer to your pathology provider for the correct swab and transport medium for PCR testing
• serology performed on blood specimens taken during the acute and convalescent stages. Interpretation of serology results can be difficult as detections can occur after vaccination (possibly up to 2 years) and in people with past infection, or it may be falsely negative in early illness. It is not recommended in children aged less than 2 years.

Infants who appear well but with a history of cough, choking, gasping or difficulty catching their breath should be reviewed and tested for pertussis, especially if they have had contact with a pertussis case.

Incubation period of Bordetella pertussis

The incubation period ranges between 4 to 21 days with symptoms usually occurring within 7 to 10 days after exposure.

Reservoir for Bordetella pertussis

Humans are the only known natural reservoir of Bordetella pertussis.

Mode of transmission of Bordetella pertussis

Bordetella pertussis is highly infectious. Person-to-person transmission mainly occurs through respiratory droplets and direct contact with respiratory secretions from an infected person.

Transmission can also occur less commonly through contact with contaminated objects and surfaces.

Secondary attack rates of 80% have been reported among susceptible household contacts. Adults, adolescents, and older children are often the source of infection in infants.

Period of communicability of pertussis

People with pertussis are considered infectious from the onset of catarrhal symptoms. Communicability gradually decreases and is negligible 3 weeks after onset of cough.

For public health purposes, a case is considered non-infectious (even if the PCR result is still positive) at whichever time is the earlier of:

• 21 days after onset of any cough
• 14 days after onset of paroxysmal cough (if the onset is known)
• when they have completed 5 days of a course of an appropriate antibiotic.

Susceptibility and resistance to pertussis

Pertussis can affect people of all ages. However, young infants are at increased risk of infection, hospitalisation, and death.

Protection from vaccination or previous infection wanes over time.

Groups at increased risk of pertussis include:

• young infants under 6 months of age
• people who have not been vaccinated against pertussis
• people who have not received a pertussis booster in the past 10 years
• people living in the same house as someone with pertussis.

Public health significance and occurrence of pertussis

Pertussis is a highly infectious respiratory illness caused by bacterial infection that disproportionately impacts young infants. Hospitalisation and mortality rates from pertussis are highest in infants aged under 1 year. However, deaths due to pertussis are now uncommon in Australia.

In Australia, there is a seasonal pattern with most cases notified during spring and summer. Epidemics of pertussis usually occur intermittently every few years. The timing of epidemic activity may vary across jurisdiction.

In 2015, more than 20,000 cases were notified nationally. Under one-quarter (or approximately 4,600 cases) of these occurred in Victoria and around one third of these Victorian cases occurred in children aged under 15 years.

Case numbers subsequently declined and were beginning to rise again in 2019 until the onset of the COVID-19 pandemic in 2020 when case numbers again decreased.

There has been a global increase in case numbers from late 2023, including marked increases in the eastern Australian states.

The source of infection in infants is often from older children, adolescents and adults. Protection from pertussis vaccination or natural immunity wanes over time. Therefore it is important to stay up-to-date with recommended vaccinations.

Current public health interventions are primarily focused on protecting young infants who are at increased risk of morbidity and mortality.

Control measures for pertussis

Preventive measures – vaccination

Vaccination is the most important preventive measure against pertussis as it reduces the risk of infection and severe illness.

However, protection is incomplete and wanes over time. Therefore, people are recommended to stay up-to-date with their vaccinations, including booster doses, and seek medical attention early if symptoms of pertussis occur.

In Australia, pertussis vaccine is only available in combination with other antigens such as diphtheria and tetanus. Combination vaccines may also include inactivated poliovirus, hepatitis B and Haemophilus influenzae type b.

Free pertussis-containing vaccination is available for eligible people through the National Immunisation Program schedule, which include:

• infants at 2 (can be given from 6 weeks of age), 4 and 6 months of age
• children at 18 months and 4 years of age
• adolescents in Year 7 (or age equivalent)
• pregnant women in every pregnancy between 20 to 32 weeks gestation
• people under 20 years who did not receive pertussis-containing vaccination in childhood, where the vaccine was not given during childhood as catch-up vaccination
• refugees and humanitarian entrants aged 20 and over.

Check the immunisation status of all children and catch-up any missed doses.

Pregnant women

Pregnant women are recommended to receive a pertussis-containing vaccine in every pregnancy ideally between 20 to 32 weeks gestation. Vaccination of pregnant women before delivery has been reported to reduce pertussis disease in infants by 80-91%.

Adult vaccination

Pertussis vaccination is recommended for any adult who wants to protect themselves from becoming ill with pertussis. People not eligible for funded pertussis-containing vaccine can obtain the vaccine through private prescription from their doctor or immunisation provider.

An adult pertussis-containing vaccine is also recommended for the following people if their last dose was more than 10 years ago:

• adults working with or caring for children, especially healthcare and childcare workers in contact with infants.
• women who recently gave birth and did not receive a pertussis-containing vaccine during pregnancy
• parents, guardians, or carers of infants aged less than 6 months
• adults 65 years of age and older as a single booster
• travellers.

Adults of any age who need a tetanus-containing vaccine can have a combined diphtheria, tetanus and pertussis (dTpa) vaccine rather than a diphtheria and tetanus (dT) vaccine. This is especially important if they have not previously had a diphtheria, tetanus and pertussis vaccine dose in adulthood.

For further guidance on pertussis vaccination refer to the Australian Immunisation Handbook – Pertussis (whooping cough).

Control of case

Early diagnosis and treatment are important to prevent onward transmission.

Antibiotic treatment reduces the infectious period and should be given as soon as possible within 21 days of cough onset. The current recommended treatment is a course of azithromycin, clarithromycin, or trimethoprim/sulfamethoxazole. Roxithromycin is not recommended. Oral suspensions for young children may be difficult to obtain and specific advice on alternatives may be required.

For antibiotic treatment recommendations refer to the current edition of the Therapeutic guidelines: antibiotic, the Royal Children’s Hospital Melbourne Clinical Practice Guidelines or your local infectious disease service.

In hospital settings, patients with pertussis should be cared for under droplet precautions in a single room while infectious.

Cases must be excluded from primary school and children's services until 21 days after the onset of cough, or until they have received 5 days of appropriate antibiotic treatment. People with pertussis should similarly be excluded from other educational settings or workplaces and also be advised to avoid contact with infants and women in the last month of pregnancy while infectious.

Control of contacts

All close contacts should be alerted of their exposure to pertussis, advised to monitor for symptoms and to seek medical care early if they become unwell.

Close contacts include:

• family and household members
• people who stayed overnight in the same room as the case
• people who have had face-to-face contact (within 1 metre) to an infectious case for at least 1 hour.

Antibiotic prophylaxis are recommended for high-risk close contacts to reduce the risk of transmission to infants aged under 6 months and people who may transmit pertussis to these infants. They are usually recommended in the following situations.

In the event of exposure in the household setting:

• expectant parents (or carers) in the last month of pregnancy
• all household members where there is an infant aged under 6 months .

In healthcare and childcare settings:

• healthcare workers in settings where there are women in their last month of pregnancy and/or infants aged under 6 months
• childcare staff who look after infants aged under 6 months
• children in childcare who have close contact with children aged under 6 months
• women in their last month of pregnancy.

Management of immunodeficient contacts should be made on a case-by-case basis.

Antibiotic prophylaxis is most useful if given as soon as possible, within 14 days, after first contact with the infectious case. There is limited evidence that antibiotic prophylaxis reduces secondary transmission in settings other than those outlined above. Regimens for antibiotic prophylaxis are the same as for treatment of cases.

For antibiotic prophylaxis recommendations refer to the current edition of the Therapeutic guidelines: antibiotic, the Royal Children’s Hospital Melbourne Clinical Practice Guidelines or your local infectious disease service.

Primary school and children’s services exclusions apply for unvaccinated close contacts aged less than 7 years old in the same room as the infectious case. These contacts must be excluded for 14 days from the last exposure to the infectious case, or until they have received 5 days of appropriate antibiotic treatment.

Control of environment

Not applicable.

Outbreak measures for pertussis

Epidemics of pertussis occurs every few years in Australia. Prevention measures focus on immunisation and education.

Outbreaks can occur sporadically and are managed by the Local Public Health Unit.