14 Pertussis (whooping cough)

14.8 Public health measures

14.8.1 Improving pertussis control

The goal of the pertussis immunisation programme is to protect those most vulnerable to severe disease; that is, infants in the first year of life. Infants can be protected either directly, by immunisation in early infancy, or indirectly, by immunisation of others with whom the infant may come into contact and hence be exposed to B. pertussis.84 The ‘cocoon strategy’ is the term used to describe the protection of infants by immunising those who are potential sources of B. pertussis.84

The field effectiveness of the cocoon strategy is yet to be demonstrated. Reinforcement and/or improvement of the current infant immunisation series (direct protection) remains the highest priority for New Zealand. More complete and timely delivery of the current immunisation series would reduce infant pertussis disease burden.85 All children attending early childhood services should be fully vaccinated for their age.

Data on the protective effects of indirect strategies is currently incomplete. Because of low coverage and the short duration of protection, plus the unknown efficacy for the protection of infants, universal adult pertussis immunisation is a lower priority at present. Targeted immunisation of adult groups who have the most contact with young and vulnerable infants is considered a more appropriate strategy. Three identified groups are (1) pregnant women, new mothers, family, and close contacts of newborns; (2) health care workers; and (3) early childhood workers. Vaccination during pregnancy is recommended and funded for women from 28 to 38 weeks’ gestation (see section 14.5.2).

Of the three target refinement groups, selective immunisation of health care workers is the most readily justified and least costly. Health care workers are at increased risk of pertussis and can transmit pertussis to other health care workers and to patients.86 Outbreaks in maternity wards, neonatal units and outpatient settings have been described.87 Fatalities occur as a result of such nosocomial spread.88

Immunisation cannot be used to control an outbreak, although action to update age-appropriate vaccination in institutional settings (schools and early childhood services) is appropriate. When an outbreak occurs, individual immunisation status should be checked and immunisation completed. In an outbreak setting, infants as young as four weeks of age can commence immunisation.

14.8.2 NotificationTop

It is a legal requirement that all cases of pertussis be notified immediately on suspicion to the local medical officer of health.

A suspected pertussis case can be confirmed if a clinically compatible illness is laboratory confirmed, or is epidemiologically linked to a confirmed case. Because transmission is by the airborne route, non-vaccinated health care personnel looking after pertussis cases should wear a mask.

14.8.3 Laboratory diagnosis of Bordetella pertussis infectionTop

PCR is the most sensitive method for diagnosing B. pertussis infection. In general, B. pertussis can be identified by PCR from most upper respiratory tract samples, including throat swabs, for up to four to six weeks after symptom onset. Serology may be useful when symptoms have been present for several weeks, at a time when PCR and culture are more likely to be negative.

The local laboratory should be consulted for the specifics of which swabs and transport media to use.

14.8.4 Antimicrobial treatment of caseTop

A number of antibiotics are available for the treatment and prophylaxis of pertussis. Erythromycin has been shown to reduce the severity and duration of clinical disease but only if started during the catarrhal phase. Antibiotics commenced after coughing paroxysms have begun have no effect on the clinical disease but do reduce the risk of spread of disease to others.89–91 Antibiotics are of limited value if started after 21 days of illness, but should be considered for high-risk contacts (eg, young infants and pregnant women). To minimise transmission to newborn infants, it is recommended that pregnant women diagnosed with pertussis in the third trimester be treated with appropriate antibiotics (see Table 14.2), even if six to eight weeks have elapsed since the onset of cough.92

In New Zealand, azithromycin and erythromycin are funded for the treatment of pertussis. Azithromycin is the recommended treatment.

Macrolide use during pregnancy, lactation and in the neonatal period is associated with an increased risk of pyloric stenosis.93, 94 With erythromycin, the risk increases with decreasing age and increased duration of treatment.95 The risk is presumed to be lower with azithromycin, although there are case reports of pyloric stenosis occurring when azithromycin has been used during pregnancy.

Parents should be informed of the risks of this complication and of the symptoms and signs of infantile hypertrophic pyloric stenosis. The infant should be monitored for this complication for four weeks after completion of treatment.89, 96, 97

Table 14.2: Recommended antimicrobial therapy and post-exposure prophylaxis for pertussis in infants, children, adolescents and adults

Age Recommended Alternative
  Azithromycina Erythromycin Clarithromycinb TMP-SMXc
Younger than 4 weeks Day 1:
10 mg/kg/day in a single daily dose

Days 2–5:
5 mg/kg/day in a single daily dose
40 mg/kg/day in 4 divided doses for 14 days Not recommended Contraindicated under age 2 months (risk for kernicterus)
1–5 months Day 1:
10 mg/kg/day in a single daily dose

Days 2–5:
5 mg/kg/day in a single daily dose
40 mg/kg/day in 4 divided doses for 14 days 15 mg/kg per day in 2 divided doses for 7 days Aged 2 months or older: TMP, 8 mg/kg/day; SMX, 40 mg/kg/day in 2 divided doses for 14 days
6 months or older and children Day 1:
10 mg/kg/day in a single daily dose (maximum 500 mg)

Days 2–5:
5 mg/kg/day in a single daily dose (max 250 mg per day)
40 mg/kg/day in 4 divided doses for 14 days (maximum 2 g/day) 15 mg/kg/day in 2 divided doses for 7 days (maximum 1 g/day) Aged 2 months or older: TMP, 8 mg/kg/day; SMX, 40 mg/kg/day in 2 divided doses for 14 days
Adolescents and adults Day 1:
500 mg as a single dose

​Days 2–5:
250 mg once daily
2 g/day in 4 divided doses for 14 days 1 g/day in 2 divided doses for 7 days TMP, 320 mg/day; SMX, 1600 mg/day in 2 divided doses for 14 days
a Preferred macrolide during pregnancy, lactation and in infants <1 month old because of risk of idiopathic hypertrophic pyloric stenosis associated with erythromycin.
b Not funded for treatment or post-exposure prophylaxis in New Zealand.
c TMP = trimethoprim; SMX = sulfamethoxazole. TMP-SMX can be used as an alternative agent to macrolides in patients aged ≥2 months who are allergic to macrolides, who cannot tolerate macrolides, or who are infected with a rare macrolide-resistant strain of Bordetella pertussis.

Adapted from: Centers for Disease Control and Prevention. 2005. Recommended antimicrobial agents for treatment and post exposure prophylaxis of pertussis. Morbidity and Mortality Weekly Report 54(RR14) 1–16.

Cases should be excluded from early childhood services, school, or community gatherings until:

Children who have culture-proven pertussis should complete their immunisation series with all of the scheduled doses recommended for their age.

14.8.5 Management of contactsTop

The local medical officer of health will advise on the management of contacts. For more details on control measures, refer to the Communicable Disease Control Manual 2012.98

A contact can be defined as someone who has been in close proximity (within one metre)99 of the index case for one 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.98

Those most at risk from pertussis and who are therefore high-priority contacts for public health follow-up are:

The evidence for the effectiveness of chemoprophylaxis of contacts is limited. Antibiotics are currently only recommended for high-priority contacts as listed above and if given within three weeks of initial exposure to an infectious case.

Health care workers are frequently exposed to B. pertussis. Although the greatest priority is given to protecting young infants and unimmunised children, there are well-documented examples of spread from staff to older adult patients. Pertussis in adults can be debilitating and can cause significant morbidity in those with respiratory disease.

Chemoprophylaxis may therefore be useful for adults exposed to a health care worker with pertussis, and infection control or public health services should normally be involved. Factors to be considered when discussing chemoprophylaxis include whether adult pertussis vaccine has been administered within the last five years, the health status of the individual who has been exposed, how recent the exposure was, and the nature of the health care or special community setting.

Where a case worked in a maternity ward or newborn nursery for more than an hour while infectious, then all babies in that ward and their parents/carers who were exposed to the case (within one metre for more than one hour) should receive antibiotics. Note: if the minimum duration of exposure is uncertain, a neonate exposed to an infectious case for less than one hour may warrant being considered a close contact and receive antibiotics.100

Any contacts, high priority or otherwise, should be advised to avoid attending early childhood services, school, work or community gatherings if they become symptomatic. Additional restrictions may be advised by the local medical officer of health, in particular if there is significant risk of transmission of infection to high-priority individuals.