Pertussis is back! Why a high index of suspicion is important for diagnosis

  27 June 2024  Dr Jeannie Knapp, GP and Primary Health Care Improvement GP Adviser, NWMPHN   

Our GP adviser Dr Jeannie Knapp provides tips on how to manage pertussis (whooping cough), after a recent rise in case numbers following a sharp decrease from 2020 to 2023.

What is the problem?

Pertussis (whooping cough) is a vaccine-preventable infectious respiratory illness caused by a bacterial infection (Bordetella pertussis). Infants are at particularly high risk of serious illness, hospitalisation and death from this infection – partly because they are too young to be fully immunised.

In the early stages of the COVID-19 pandemic there was a rapid decrease in notifications of pertussis in Victoria, followed by a consistently low number throughout the period.

However, this year there has been a rapid increase. By mid-June there were 904 cases recorded in Victoria, compared to just 85 at the same point in 2023. These numbers are now approaching pre-pandemic levels, when pertussis epidemics occurred every three or four years.

Why is diagnosis important?

Early diagnosis and treatment of pertussis is important to prevent onward transmission to vulnerable population groups – especially infants. Most deaths from pertussis are in infants under 6 months of age. Adults and adolescents are the main reservoirs of infection. However, previous vaccination with variable penetration means presentations are often atypical.

How does pertussis present clinically?

The incubation period of pertussis can range from seven to 20 days. Patients are typically infectious for the first 21 days. The classic “textbook” infection is divided into phases:

  • The catarrhal phase, which can be indistinguishable from a common cold and may last one to two weeks.
  • The paroxysmal phase, with paroxysms of intense coughing often lasting several minutes and accompanied by a whoop, or gasping, or gagging. There may be vomiting after the cough. This phase can run for two to eight weeks, but may last up to three months.

Previous vaccination often results in a modified illness that does not present with the classic textbook features. Older children, adolescents and adults may just present with a chronic cough.

How is pertussis diagnosed?

A high index of suspicion is needed to diagnose pertussis. It is particularly important to consider in anyone with a prolonged cough – present for longer than 14 days – and if they have any one of the following symptoms:

  • paroxysmal cough (bouts of intense coughing followed by long breaks)
  • post-coughing vomiting
  • inspiratory whoop

The most accurate diagnosis is by nasopharyngeal PCR swab. These will typically only be positive in the first 21 days of the illness. Serological testing can assist in confirming a retrospective diagnosis.

What is the treatment for pertussis?

Infants under 6 months have the highest morbidity and mortality from pertussis, and may require hospitalisation.

If pertussis is suspected, start treatment before waiting for test results. Antibiotic treatment is recommended – however, they may not change the clinical course of the illness. Antibiotics reduce the transmission to contacts and are therefore important in managing spread. From Therapeutic Guidelines (eTG), azithromycin is the preferred antibiotic.

While infectious, people with pertussis should be excluded from work and avoid contact with infants and women in the last month of pregnancy. This is until 21 days after the onset of cough, or until they have received five days of appropriate antibiotic treatment.

What about pertussis contacts?

Contacts of pertussis are defined as people have been within one metre of an infectious pertussis case for more than one hour.

From eTG:

In community settings, prescribe pertussis prophylaxis to the following patient groups if they are contacts of a pertussis case:

  • infants younger than six months
  • women in the last month of pregnancy
  • individuals who may transmit pertussis to infants younger than six This includes children and adults who:
    • have contact with the pertussis case in a childcare setting (need for prophylaxis varies depending on the whether an outbreak has occurred, the age of children at the childcare setting and vaccination statusseek advice from the local public health authority)
    • reside in a household with an infant less than six months of age; if the pertussis case is a member of the household, all household members should receive prophylaxis
    • reside in a household with a woman in the last month of pregnancy; if the pertussis case is a member of the household, all household members should receive prophylaxis.

How can we prevent pertussis?

Vaccination is the most important preventive measure against pertussis.

  • Check the immunisation status of all children and catch-up any missed doses.
  • Pregnant women are recommended to receive a pertussis-containing vaccine in every pregnancy, ideally between 20 to 32 weeks gestation.
  • Pertussis vaccination is recommended for any adult who wants protection from the bacterium.
  • Consider a “cocooning” strategy for new babies, recommending all adults and children in contact are up-to-date with pertussis vaccination.

More information:

HealthPathways Melbourne – pertussis

Victorian Department of Health – pertussis

Australian Government Immunisation Handbook – pertussis

RACGP: Pertussis in Australia today

The Royal Children’s Hospital, clinical practice guidelines: Whooping cough (pertussis)

Medscape: Pertussis clinical presentation