Pertussis

New Zealand has continued to experience cyclic outbreaks of pertussis, occurring every few years, in recent decades. This is in part due to historically low immunisation rates and because immunity from both natural infection and immunisation wanes over time.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

The objectives of surveillance for pertussis are:

• to monitor and analyse the epidemiology of the disease, with emphasis on those at high risk of severe disease or complications, particularly infants
• to monitor the impact of immunisation
• to report on findings to inform effective and efficient prevention strategies.

The priority of the prevention strategies against pertussis is to protect infants by passive immunity transfer from their mothers with booster immunisation during each pregnancy, and timely immunisation of infants.

A clinically compatible case characterised by cough and one or more of:

• paroxysms of cough
• cough ending in vomiting, cyanosis or apnoea
• inspiratory whoop.

Infants are less likely to have the inspiratory whoop and are more likely to present with gagging, gasping, cyanosis, apnoea, or non-specific signs such as poor feeding or seizures.

Adults and children partially protected by vaccination can present with illness ranging from a mild cough illness to classic pertussis.

Laboratory definitive evidence for a confirmed case requires: isolation of Bordetella pertussis or detection of B. pertussis nucleic acid, preferably from a nasopharyngeal swab.

Laboratory suggestive evidence for a probable case requires: B. pertussis toxin IgG test of > 100 IU/ml or a significant increase[1] in antibody levels between paired sera at the same laboratory. Serology should only be requested for public health purposes after consultation between the Medical Officer of Health and the local microbiologist.

Note

There are several laboratory tests available for the diagnosis of pertussis and the timing of the test impacts on its sensitivity. Appropriate tests and specimens should be discussed with the testing laboratory or ESR.

A negative test does not necessarily rule out pertussis: consider exposure, clinical compatibility, the test used and the timing of the test.

Polymerase Chain Reaction (PCR)

PCR should be considered the diagnostic method of choice, unless the presentation is delayed until 4 weeks after onset of symptoms, or 3 weeks after the onset of paroxysmal cough. After that sensitivity declines as the amount of bacterial DNA in the nasopharynx diminishes. PCR is 2–3 times more likely to be positive than culture when symptoms of classic pertussis are present (eg, 2 weeks of paroxysmal cough). PCR can be affected by specimen collection but is less affected by prior antibiotic therapy since the organism does not need to be viable to be positive by PCR.

Culture

Culture is only useful during the catarrhal and very early paroxysmal phase of illness. The sensitivity of nasopharyngeal culture decreases rapidly after the onset of cough.

Culture sensitivity is reduced by antibiotic treatment, immunisation, duration of illness and can also be affected by specimen collection, transportation and isolation techniques. Cultures are rarely positive after 2 weeks from the onset of the catarrhal stage of the illness, or 1 week of paroxysmal cough, or for more than a few days after antibiotic treatment. Cultures may also take up to 2 weeks to be finalised, so the results may not be clinically useful.

Serology

The sensitivity and specificity of serology is low. Serology cannot be used as a confirmatory test. Therefore the use of serology is not recommended, except for public health purpose after consultation between the Medical Officer of Health and the local microbiologist. Serology can then sometimes be used late in the course of illness, generally when the patient is no longer infectious. Serologic tests measure antibodies that could result from either infection or vaccination. Anti-pertussis toxin IgG is the best serological marker of infection. IgA assays lack adequate sensitivity and specificity and should not be used for diagnosis.

• Under investigation: A case that has been notified, but information is not yet available to classify it as suspect, probable or confirmed.
• Suspect (in children under 5 years of age): Any paroxysmal cough with whoop, vomit or apnoea for which there is no other known cause.
• Probable: A clinically compatible illness where the cough is lasting longer than 2 weeks. However in situations where serology has been requested after consultation between the Medical Officer of Health and the local microbiologist, a clinically compatible illness with laboratory suggestive evidence will also be considered as probable.
• Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence, or is epidemiologically linked[2] to a confirmed case.
• Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Usually 7–10 days, ranging from 5–21 days.

Droplets of respiratory, oral or nasal secretions. Indirect spread via contaminated objects occurs rarely.

Highly communicable in the catarrhal stage before the paroxysmal cough stage, and during the first 2 weeks of the paroxysmal stage of the cough. Transmissibility gradually decreases after that.

For control purposes, the communicable stage lasts from the catarrhal stage to 3 weeks after the onset of paroxysmal cough in a case not treated with antimicrobials. When treated with an effective antibiotic (eg, azithromycin), infectivity lasts until 2 days of antibiotics have been taken. This lengthens to 5 days if other antibiotics are used (eg, erythromycin).[3]

Laboratory definitive evidence

Detection of Bordetella pertussis nucleic acid by PCR testing, preferably from a nasopharyngeal swab.

Laboratory suggestive evidence

Detection of B. pertussis toxin IgG test of > 100 IU/ml or a significant increase in antibody levels between paired sera at the same laboratory. Serology should only be requested for public health purposes after consultation between the medical officer of health and the clinical microbiologist.

Health practitioners should notify the local medical officer of health on suspicion of Bordetella pertussis during the initial assessment of the person.

If B. pertussis is suspected, include clinical information, symptom onset and vaccination status on the sample request form. 

In periods of low pertussis activity, the medical officer of health or other public health service staff may discuss urgent cases with the on-call clinical microbiologist, where there is a high index of suspicion for B. pertussis, so that laboratory staff are aware of the urgency and can prioritise the sample for prompt processing. Testing may not be necessary for cases with an epidemiological link to a confirmed case.

In periods of high pertussis activity, testing may not require discussion with the medical officer of health. Testing should be prioritised towards protecting high priority contacts from infection - especially infants and pregnant people. Testing is not required for cases with an epidemiological link to a confirmed case.

Note: There are several laboratory tests available for the diagnosis of B. pertussis and the timing of the test impacts on its sensitivity. A negative test does not necessarily rule out B. pertussis: consider exposure, clinical compatibility, the test used and the timing of the test. For further testing advice please contact the clinical microbiologist. There is no reliable serological test for acute infection or immunity to B. pertussis.

For urgent polymerase chain reaction (PCR) processing the medical officer of health should discuss with the clinical microbiologist. The turnaround time for a prioritised test may still take 24-36 hours after arrival at the laboratory.

1) Bordetella pertussis polymerase chain reaction (PCR) (nucleic acid amplification test)

Bordetella pertussis PCR is the recommended test for diagnosing the bacteria B. pertussis in people where the symptoms have been present for less than 3 weeks. Positive results are more likely within 10-14 days of symptom onset. After 4 weeks of cough, the amount of bacterial DNA in the nasopharynx rapidly diminishes, increasing the risk of a false-negative result. [1, 2, 3]

PCR testing ensures a fast turnaround time when rapid confirmation of the diagnosis is likely to change management of the case or their contacts. 

2) Serology

Most laboratories in Aotearoa New Zealand do not offer serology testing for B. pertussis.

• Serology (Immunoglobulin G IgG)

Serology is not recommended, except when requested by a medical officer of health after discussion with a clinical microbiologist if the use of a PCR test is not possible. This is because the sensitivity and specificity of serology is low and cannot be used as a confirmatory test of infection or vaccination. The presence of B. pertussis IgG is not a reliable indicator for a person’s immune status and should not be used in this context.

• Serology (Immunoglobulin A IgA)

A serum antibody test may be useful for retrospective diagnosis. Serum IgA antibodies may not become positive until 2 weeks after symptom onset. IgA antibodies are not stimulated by vaccination, so a positive result in a vaccinated person indicates past or current infection. IgA tests lack adequate sensitivity and specificity especially in infants and should not be used for diagnosis.

3) Culture

Culture is no longer routinely performed for diagnostic purposes. PCR testing is between two and six times more sensitive than culture and is the preferred diagnostic method.

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

Any person awaiting a pertussis test result should be advised to stay at home and away from work, school, early childhood services, or other institutions while they await their test results.

See Appendix 5: Escalation pathways for more information

The highest priority should generally be given to the following cases:

• under 5 years of age, the younger cases before the older cases
• women known to be in the last month of pregnancy
• cases with a pre-existing health condition that may be exacerbated by a pertussis infection
• cases known to have close contacts, work or attend a setting with someone particularly vulnerable to pertussis (young child with < 3 doses of pertussis-containing vaccine, a woman in the last month of pregnancy or person with a pre-existing health condition that may be exacerbated by a pertussis infection).

In consultation with the attending medical practitioner, ascertain pertussis immunisation status and determine whether there are close contacts for whom chemoprophylaxis is appropriate.

Ideally, a nasopharyngeal swab should be collected from all suspected cases of pertussis. However, testing may not be necessary or appropriate for cases with an epidemiological link to a confirmed case, or in outbreak situations.

Any person awaiting a pertussis test result should be advised to stay at home and away from work, school, early childhood services, or other institutions while they await their test results. 

Exclude the case from school, early childhood services, other institutions or work until they have received at least two days of azithromycin (this lengthens to five days if other antibiotics, are used) [3] Or exclude them for 3 weeks from the date of onset of typical paroxysms of cough or until the end of the cough, whichever comes first. 

Treatment for pertussis has been shown to reduce the time a case is infectious. Therefore, antibiotic therapy is recommended for cases up to 21 days after the onset of cough. 

Antibiotic therapy administered in the catarrhal stage (within the first 1-2 weeks) may modify the clinical course of the illness (based on suboptimal evidence), but does not reduce duration of illness when administered after the onset of the paroxysmal cough. Antibiotic therapy is indicated before test results are received if the clinical history is strongly suggestive of pertussis or the person is at high risk of severe or complicated disease (e.g. an infant). [4,5,6,7] 

Cases remain infectious for 21 days following the onset of cough. There is no evidence that initiating treatment after this will modify the course of the illness or reduce infectivity. 

Recommended antibiotics include azithromycin, cotrimoxazole, and erythromycin as an alternative to azithromycin.  

Advise the case and their caregivers of the nature of the infection and its mode of transmission.

A contact can be defined as someone who has been in close proximity (within 2 metres) of the index case for 1 hour or more, during the case’s infectious period. Contacts include household members, those who have stayed overnight in the same room, and those who have had face-to-face contact with the case.

Intensive public health follow-up of all contacts is not usually necessary or effective in preventing community transmission, although raising general awareness and promoting on-time immunisation is important.

The primary goal of public health follow-up for pertussis contacts is to protect infants, pregnant women, and people at high risk of severe or complicated illness.

High priority contacts for public health follow-up are therefore:

• children under 12 months old
• children and adults who live with, or spend much of their time around a child under 12 months old, including health care and education settings
• pregnant women (particularly in the last month of pregnancy)
• individuals that are at high risk of severe illness or complications because a pre-existing health condition that may be exacerbated by a pertussis infection (for example those with chronic respiratory conditions, congenital heart disease or immunodeficiency).

Factors to consider when determining public health follow-up and intervention include:

• degree of exposure. Most contacts at early childhood services, schools or work or who have only shared vehicle space or only had casual contact are not usually considered contacts for the purposes of public health follow-up, other than providing information and observation
• immunisation status. For example whether there is clearly documented full immunisation history or recent boosters[5]
• the health status of the contact
• side effects of prophylactic antibiotics.

Children and staff at early childhood services, especially partially immunised children, should be observed for respiratory tract symptoms for 3 weeks after last exposure to an infectious case.

Any contacts (high priority or otherwise) should be advised to avoid attending early childhood services, school, work or community gatherings if they become symptomatic. It is important to clearly explain that the early stage of pertussis is catarrhal, with symptoms that are indistinguishable from those of minor respiratory tract infections, and is highly contagious.

In general, susceptible contacts[6] working or living with someone particularly vulnerable to pertussis (in particular: young child with < 3 doses of pertussis-containing vaccine, woman in the last month of pregnancy or person with a pre-existing health condition that may be exacerbated by a pertussis infection) should be given prophylaxis with antibiotics and not be excluded while taking prophylaxis as long as they don’t have any symptom, or, in the absence of prophylaxis, be excluded/avoid close contact for 14 days after the last exposure to an infectious case.

Additional restrictions may be advised by the local Medical Officer of Health, in particular where there is a significant risk of transmission to high priority individuals. For example health care workers who work with children under 12 months old (such as on paediatric and maternity wards).

Unless current immunity is likely, high priority contacts should be offered a dose of a pertussis containing vaccine[7] (only doses on the national immunisation schedule are funded, including the 11 year old booster and boosters during pregnancy (recommended from 16 weeks’ gestation).

Advise any unimmunised or partially immunised individuals to be fully immunised.

Not applicable.

Clean and disinfect surfaces and materials contaminated by respiratory secretions.

Encourage immunisation of pregnant women from 16 weeks’ gestation at every pregnancy.

Encourage on-time immunisation, particularly for infants at 6 weeks, 3 months and 5 months.

Encourage timely immunisation of older children against pertussis at aged 4 and 11 years as per the Immunisation Handbook 2020 (Ministry of Health) [8]

Encourage (re-)vaccination of immunosuppressed patients with pertussis-containing vaccine according to the existing guidance[9] (funded).

Encourage close family contacts of young infants, such as grandparents, fathers and partners to have a booster dose of pertussis vaccine to reduce spread of the disease. Older siblings should be up-to-date with their immunisations.

Encourage a booster dose against pertussis every 10 years to all lead maternity carers and other health care personnel who work in neonatal units and other clinical settings (such as GPs, practice nurses and Well Child providers), where they are exposed to infants.

Encourage a booster dose against pertussis every 10 years to all those living or working with people with a pre-existing health condition that may be exacerbated by a pertussis infection, especially health care workers.

Encourage a booster dose against pertussis every 10 years to all early childhood workers.

Promote behaviours that protect infants, such as encouraging people with a cough to keep their distance from babies.

Promote behaviours that prevent the transmission of communicable respiratory diseases.

Ensure complete case information is entered into EpiSurv.

If a cluster of cases occurs, contact 0800GETMOH - CD option, and outbreak liaison staff at ESR, and complete the Outbreak Report Form.

1. Evaluation of real-time PCR for diagnosis of Bordetella pertussis infection. Available from https://link.springer.com/article/10.1186/1471-2334-6-62 
2. Impact of polymerase chain reaction on clinical pertussis research: Finnish and Swiss experiences. Available from https://pubmed.ncbi.nlm.nih.gov/8940220/ 
3. Clinical evaluation and validation of laboratory methods for the diagnosis of Bordetella pertussis infection: Culture, polymerase chain reaction (PCR) and anti-pertussis toxin IgG serology (IgG-PT). Available from https://pubmed.ncbi.nlm.nih.gov/29652945/ 
4. Pertussis, Centers for Disease Control and Prevention website. Available from https://www.cdc.gov/pertussis/index.html 
5. Pertussis Clinical Guidelines, Starship. Available from https://starship.org.nz/guidelines/pertussis/ 
6. Committee of Infectious disease, Redbook. Available from https://publications.aap.org/redbook/book/755/Red-Book-2024-2027-Report-of-the-Committee-on?autologincheck=redirected 
7. Antibiotics for whooping cough (pertussis). Available from https://pubmed.ncbi.nlm.nih.gov/17636756/ 
8. A randomized, placebo-controlled trial of erythromycin estolate chemoprophylaxis for household contacts of children with culture-positive bordetella pertussis infection. Available from https://pubmed.ncbi.nlm.nih.gov/10506267/ 
9. Review of the evidence for the use of erythromycin in the management of persons exposed to pertussis. Available from https://pubmed.ncbi.nlm.nih.gov/9593483/ 
10. Use of antibiotics in the prevention and treatment of pertussis. Available from https://pubmed.ncbi.nlm.nih.gov/15876929/ 

• Altunaiji SM, Kukuruzovic RH, Curtis NC, Massie J. 2011. Antibiotics for whooping cough (pertussis) (Review). Cochrane Library.
• Ministry of Health. 2020. Immunisation Handbook 2020 Wellington: Ministry of Health.
• CDC. Pertussis Home webpages. Postexposure Antimicrobial Prophylaxis. Information for Health professionals. Updated: August 7, 2017.
• CDC. 2005. Recommended antimicrobial agents for treatment and postexposure prophylaxis of pertussis. 2005 CDC Guidelines. Morbidity and Mortality Weekly Report. Recommendations and Reports 54(RR-14).
• CDC. 2013. Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccine (Tdap) in Pregnant Women — Advisory Committee on Immunization Practices (ACIP), 2012. Morbidity and Mortality Weekly Report. Vol. 62, No. 7, 22 February.
• Department of Health and Ageing, Australia. 2015. Pertussis National Guidelines for Public Health Units. Version 3.0. April.
• Dodhia H, Crowcroft N, Bramley JC, et al. 2002. UK Guidelines for the use of erythromycin chemoprophylaxis in persons exposed to pertussis. Journal of Public Health Medicine 24: 200–06.
• Health Protection Agency, UK. 2011. HPA Guidelines for the Public Health Management of Pertussis. February.
• Ministry of Health. 2009. National Immunisation Register.
• Ministry of Health, NSW. 2009. Pertussis Response Protocol for NSW Public Health Units. New South Wales: NSW Government.
• Public Health England, UK. 2016. Guidelines for the Public Health Management of Pertussis in England. London: Public Health England

[1]    A ‘significant increase’ is generally taken as a fourfold rise in titre, however interpretation of serology results should be discussed with the testing laboratory or ESR.

[2]   A epidemiological link is established when there is: contact between two people at a time when one of them is likely to be infectious (from the catarrhal stage, approximately 1 week before, to 3 weeks after onset of cough) AND the other has an illness which starts within 5 to 21 days after this contact AND at least one case in the chain of epidemiologically linked cases (which may involve many cases) is a confirmed case with either laboratory definitive or laboratory suggestive evidence.

[3]    Although Public Health England guidelines (updated 9 December 2016) recommend an exclusion of 2 days for all excluded cases, the clearance of B. pertussis with other antibiotics may not be as rapid.

[4]    See the New Zealand Formulary for Children and New Zealand Formulary for Adults.

[5]   The Immunisation Handbook 2017 currently recommends boosters (funded) for pregnant women between 28–38 weeks gestation in each pregnancy and boosters (not funded) at 10–yearly intervals for certain groups (pp. 383–385). Recommended timing will be kept under review, given that immunity wanes after 5–10 years from the last pertussis vaccine dose (MMWR Vol. 54 No. RR-14 December 9, 2005).

[6]   Susceptible contacts are defined as those who are not fully immunised for their age, or if they are over 16 years of age and have not received a booster of pertussis-containing vaccine in the last 5 years.

[7]   Pertussis vaccine should be offered in every pregnancy (currently funded for pregnant women between 28-38 weeks gestation). Vaccination of pregnant women is likely to result in increased immunity in the newborn infant, as well as in the mother (also see Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccine (Tdap) in Pregnant Women — Advisory Committee on Immunization Practices (ACIP), 2012. MMWR. Vol. 62, No. 7, 22 February 2013).

[8]    Refer to the 'Funded vaccines for special groups' chapter of the Immunisation Handbook 2017.

[9]    Refer to the 'Funded vaccines for special groups' chapter of the Immunisation Handbook 2017.