Pertussis (whooping cough)

Notification requirement for pertussis

Pertussis infection is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centres exclusions

Cases should be excluded for 21days after the onset of cough or 5 days after commencing effective antibiotic treatment.

Unimmunised contacts aged less than 7 years old in the same room as the case must be excluded from primary school and children's services centres for 14days from the last exposure to infection, or until they have taken 5days of a course of effective antibiotic treatment.

Infectious agent of pertussis

Bordetella pertussis.

Identification of pertussis

Clinical features

The catarrhal stage may be indistinguishable from a viral upper respiratory tract infection. The infection damages respiratory epithelium, producing respiratory obstruction and paroxysmal coughing. There is often a characteristic ‘whoop’. This is a crowing sound during inspiration preceding a bout of coughing. Infants aged less than 6 months and adults may not have this classical whoop. Paroxysms frequently end with the expulsion of clear, tenacious mucus, often followed by post-tussive vomiting. There is little fever.

Apnoea, seizures and encephalopathy may occur in very severe cases.

Pneumonia is the most common cause of death. Fatal encephalopathy, presumably hypoxic, and severe weakness from repeated vomiting, occasionally occur.

Method of diagnosis

Pertussis can be diagnosed on a clinical basis if the patient has an acute illness lasting more than 14 days without another apparent cause, a classical paroxysmal cough with whooping and post-tussive vomiting.

However, bouts of coughing may occur without whoops or vomiting, and the disease may only be suspected if the patient is a contact of a known case. Apnoea may be the only manifestation in infants.

Laboratory confirmation can be problematic, but should be sought where possible. A nasopharyngeal aspirate or swab is the best specimen to obtain to culture the bacterium, although polymerase chain reaction (PCR) testing of such specimens has largely overtaken culture in recent years. The likelihood of cultures being positive is reduced 21 days after the cough onset or if effective antimicrobial therapy has commenced against B. pertussis. Serology using B. pertussis–specific IgA may be falsely negative, but a positive result is highly reliable in the presence of appropriate symptoms in someone not recently (that is, within 1–2 years) vaccinated.

Incubation period of Bordetella pertussis

The incubation period is usually between 6 and 20 days. It is most commonly about 14 days.

Public health significance and occurrence of pertussis

Whooping cough is a distressing and often serious illness, particularly in children under 1 year of age. The mortality rate is 0.5 per cent in infants under 6months. High immunisation levels reduce the number of cases, and good nutrition and medical care reduce case fatality. Many vaccinated adults may have mild infection and act as a source of infection for younger children.

Australia experiences an epidemic of whooping cough about every 3 or 4 years. In 2013, more than 12 000 cases were notified nationally, with just under one-quarter of these occurring in Victoria. There is a clear seasonal pattern, with 64 per cent of notifications occurring during the spring and summer months.

Since it is not possible to completely control pertussis with the current vaccine, the highest priority should be given to protecting infants less than 12 months old.

Reservoir for Bordetella pertussis

Humans are the only known natural reservoir of B. pertussis.

Mode of transmission of Bordetella pertussis

B. pertussis is highly infectious. It may be spread from person to person by close contact, usually by respiratory aerosols, infecting 70–100 per cent of susceptible household contacts.

Period of communicability of pertussis

Pertussis is highly communicable in the early catarrhal stage, before the onset of paroxysmal cough. Thereafter, communicability decreases and becomes negligible after about 3 weeks. When treated with a macrolide antibiotic, the period of infectivity usually lasts 5 days or fewer after therapy starts.

Susceptibility and resistance to pertussis

Maternal antibodies do not protect newborns against infection. Severity is greatest in young infants, whereas milder and atypical cases occur in all age groups.

Incomplete immunisation, waning immunity and the fact that vaccine efficacy is 70–80 per cent results in cases occurring in older children and adults, with the potential for subsequent transmission to vulnerable infants. Lifelong immunity is not guaranteed, even after clinical disease.

Control measures for pertussis

Preventive measures

Educate the public regarding the dangers of whooping cough, and the advantages of initiating immunisation at 2 months of age and subsequently adhering to the immunisation schedule (DTPa at 2, 4 and 6 months, and 4 and 10–15 years of age).

Delay immunisation only for significant intercurrent infection or an evolving neurological disorder. Minor respiratory infections are not a contraindication to immunisation.

Control of case

Antibiotics will have little effect on the clinical course of disease, but can reduce the risk of transmission if commenced within 21 days of cough onset. Treatment generally consists of azithromycin, clarithromycin or erythromycin. There is currently no evidence that roxithromycin is effective. If a macrolide is not tolerated, cotrimoxazole may be considered.

A patient who has been coughing for more than 21 days is no longer infectious, and antibiotic treatment and school exclusion are not needed. Antibiotic treatment is required if there is complicating pneumonia. Consult the current version of Therapeutic guidelines: antibiotic.

Control of contacts

Erythromycin should not be given if more than 14 days have elapsed since the first contact with the infectious case (doses and duration as for cases). In special circumstances, such as a high-risk exposure for an infant contact, antibiotics may be given within 21 days of first contact with an infectious case.

Antibiotics rarely prevent secondary transmission and should be limited to household or childcare contacts at high risk of severe complications that have had direct contact with an infectious case, such as:

• infants under 12 months of age, regardless of vaccination status
• any child aged between 12 and 24 months who has received less than 3 doses of pertussis vaccine
• any women in the last month of pregnancy
• any child or adult who attends or works at a childcare facility, or who has significant contact with infants under 12 months of age.

Prophylactic antibiotics should not be given if more than 14 days have elapsed since the first contact with the infectious case (doses and duration as for cases). In special circumstances, such as a high-risk exposure for an infant contact, antibiotics may be given within 21 days of first contact with an infectious case.

Control of environment for pertussis

Not applicable.

Outbreak measures for pertussis

See ‘Control of contacts’.

Clusters of infection are managed on a case-by-case basis. Contact the department for further advice.

Advice for clinicians – pertussis

Pertussis is highly infectious. Transmission is by respiratory droplets and direct contact with discharges from respiratory mucous membranes of infected persons. Secondary attack rates of 80 per cent among susceptible household contacts have been reported.

Infants under 6 months of age are at highest risk of complications and death.

Incidence of pertussis

In Victoria, the number of notified cases of pertussis rose 500 per cent from 2005 to 2010.

Diagnosis of pertussis

Diagnosis of pertussis is often delayed, because initial symptoms can be mild and the typical 'whoop' is not necessarily present, especially in adults or vaccinated children.

For children under 2 years of age, nucleic acid testing (NAT)/PCR is preferred and can be positive up to 5 weeks after onset of illness. Serology is not recommended. Cultures can also be requested, but may take as long as 2 weeks.

For people 2 years and older, NAT/PCR is also recommended. IgA serology (ideally both acute and convalescent) can also be done. Interpretation can be problematic, because IgA may be elevated in vaccinated patients and patients with past infection, or falsely negative when taken early in the disease course.

To combat the current increased incidence, it is important to think, test and treat pertussis early.

Nucleic acid testing/PCR

NAT/PCR should be considered the diagnostic method of choice, and can be positive for up to 4 weeks after the onset of illness. After the fourth week of cough, sensitivity declines as the amount of bacterial DNA in the nasopharynx diminishes. Nasopharyngeal swabs or aspirate are the best specimens to obtain within 21 days of cough onset.

Serology

The sensitivity and specificity of serology is low. Serology may be useful if a clinically compatible illness has been present for more than 2 weeks, but it is not recommended in children less than 2 years old.

IgA and IgG may be elevated for an unknown period (possibly 2 years) in adults and adolescents after vaccination.

Pertussis can also be diagnosed on a clinical basis if the patient has an acute coughing illness lasting 14 days or longer without other apparent cause, and any one of paroxysms, whoop, or post-tussive vomiting. However, laboratory confirmation should be sought.

Testing

Testing of cases with contacts who are less than 6 months old is particularly important to limit potential transmission. Infants who appear well, but with a history of cough, choking, gasping and difficulty catching breath should also be reviewed for pertussis.

Recommended antibiotic treatment for pertussis

Early detection means less population infection.

Antibiotics given early in the catarrhal stage may ameliorate the disease, but may have little effect on symptoms if given later. Importantly, antibiotics reduce the period of communicability and should be initiated as soon as possible.

Roxithromycin is not recommended. The current recommended treatment is a course of azithromycin, clarithromycin or erythromycin (only azithromycin should be used in a child under 1 month of age).

In babies less than 1 month old, erythromycin is not recommended because of concerns it may cause pyloric stenosis, and clarithromycin is not recommended because safety data are not available.

For more details refer to the latest edition of Therapeutic guidelines: antibiotic.

A person who has been coughing for more than 21 days is no longer infectious. Therefore, antibiotic treatment, and school or childcare exclusion are not required anymore.

Contacts of pertussis cases

Close contacts include:

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

There is little evidence that antibiotic prophylaxis reduces secondary transmission outside of household settings.

Therefore, antibiotic prophylaxis should be limited to:

• high-risk contacts, including pregnant women in the last month of pregnancy and infants less than 6 months old
• household contacts who may transmit pertussis to these high-risk contacts.

Antibiotic prophylaxis is only useful if given as soon as possible after first contact with an infectious index case and no later than 2 weeks after first contact.

In any setting, high-risk contacts include:

• healthcare staff who have had face-to-face contact with a case within 1 m for at least 1 hour, and who work in a setting where women in the last month of pregnancy or infants less than 6 months old are present
• childcare staff who have not had a pertussis-containing vaccine in the past 10 years and look after infants aged less than 6 months
• women in their last month of pregnancy (as they may be infectious at time of delivery and pose a risk to other new parents and neonates).

Recommended antibiotics for prophylaxis are the same as for treatment.

Immunisation for pertussis

People who have been vaccinated for pertussis are still at risk of contracting pertussis (vaccine effectiveness is around 85 per cent). Vaccination can prevent or reduce the severity of symptoms, making the diagnosis more difficult (for example, lack of a ‘whoop’).

Vaccine immunity and natural immunity wane after 6–10 years.

If the patient has already been infected, then vaccination will not prevent illness. However, complete vaccination remains the most important preventive measure for pertussis control.

Immunisation – children and adolescents

Check the immunisation status of all children and catch-up any missed doses. The routine recommended schedule in 2015 for pertussis vaccination is at:

• 2 (from 6 weeks of age), 4 and 6 months
• 4 years of age (from 3.5 years of age)
• 12–16 years of age.

From 2016 it will be recommended for 12–13 year olds.

Immunisation – adults

An adult pertussis-containing vaccine (Adacel® or Boostrix®) is recommended from 10 years of age as a single dose for the following groups, regardless of their diphtheria, tetanus or pertussis vaccination history:

• adolescents aged 12–16 years in 2015, and adolescents aged 12–13 years from 2016
• pregnant women in the third trimester of every pregnancy (from 28 weeks gestation)
• women immediately postpartum who gave birth on or after 1 June 2015, and up to the time when their baby turns 6 months of age, if they have not received a pertussis-containing booster in the past 10 years
• all other parents/guardians from the third trimester of pregnancy, up to the time when their baby turns 6 months of age (for babies born on or after 1 June 2015), if they have not received a pertussis-containing booster in the past 10 years
• adults working with or caring for young children, especially healthcare workers and childcare workers in contact with infants
• adults 65 years of age and older should be offered a single booster if they have not received one in the previous 10 years
• any adult wishing to receive a dose of an adult pertussis booster vaccine to reduce the chance of contracting pertussis.

From 1 June 2015, Boostrix® will be provided for free by the Victorian Government for pregnant women and new parents, in line with the above recommendations.

For more information, visit the Immunise Australia Program.