Causative OrganismPertussis is caused by a bacterium, Bordetella pertussis; a gram-negative bacillus, which colonises the upper respiratory tract. There are other organisms such as Bordetella parapertussis, Mycoplasma pneumoniae and Chlamydia pneumoniae, which can cause a pertussis-like illness. Signs, Symptoms and ComplicationsPertussis disease can be divided into three stages: 1) Catarrhal stage - Can last 1-2 weeks and includes a runny nose, sneezing, low-grade fever, and a mild cough (all similar symptoms to the common cold).
2) Paroxysmal stage - Usually lasts 1-6 weeks, but can persist for up to 10 weeks.
- The characteristic symptom is a burst, or paroxysm, of numerous, rapid coughs.
- At the end of the paroxysm the patient suffers from a long inhaling effort that is characterized by a high-pitched whoop.
- Infants and young children often appear very ill and distressed, and may turn blue and vomit. Infants generally do not have the characteristic “whoop” sound.
3) Convalescent stage - May last for months.
- Although the cough usually disappears after 2-3 weeks, paroxysms may recur whenever the patient suffers any subsequent respiratory infection.
- Disease is more severe in infants and young children.
- The cough may persist for up to 3 months and is often associated with vomiting.
- Severe coughing may lead to brain hypoxia. In 1 to 3 per thousand children, whooping cough leads to permanent brain damage, paralysis, deafness or blindness.
- The disease is usually milder in adolescents and adults, consisting of a persistent cough similar to that found in other upper respiratory infections. However, these individuals are still able to transmit the disease to others, including unimmunised or incompletely immunised infants.
- Pertussis immunity wanes over time; both following natural disease and vaccination (immunity lasts 5 – 10 years). Re-infection may present as a persistent cough, rather than typical pertussis.
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| Infant with Pertussis cough. Courtesy of the Pennsylvania Chapter of the American Academy of Pediatrics. |
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Method of Transmission- Pertussis is spread through the air by infectious droplets and is highly contagious infecting 70 to 100% of susceptible household contacts and 50 to 80% of susceptible school contacts.
- The incubation period is commonly five to 10 days, with an upper limit of 21 days.
- Many babies contract pertussis from their older siblings or their parents.
Public Health Importance- Pertussis kills about 250,000 children worldwide each year.
- Many children are left with brain damage from pertussis infection.
- Pertussis is highly infectious and around 90% of non-immune household contacts will contract it.
- Most countries have epidemics every three to five years. In unvaccinated populations, these outbreaks can be very large. In vaccinated populations, smaller outbreaks with greatly reduced mortality and morbidity continue to occur every 3 to 4 years.
- Both hospitalisation and deaths are likely to be underestimated as infants, particularly preterm, may either present without characteristic symptoms or be misclassified as sudden infant death syndrome.
- Maternal antibody does not give adequate protection against pertussis, so babies can be infected before they are old enough to be vaccinated.
- It has been estimated that up to 20% of severe adult coughs 1-3 months untreated, could be caused by pertussis infection. These individuals are a significant reservoir of infection.
- Some countries such as USA, Australia and Canada are now identifying higher rates of pertussis infection, especially in adolescents and adults. The cause of this is not yet fully explained; these countries are all introducing pertussis boosters for adolescents.
- Those most at risk are young babies. Around 75% of those who catch pertussis before the age of 6 months require hospitalisation. Children under 12 months who are ill enough to be admitted to hospital have a 1 in 200 chance of dying of whooping cough.
- Currently available vaccines prevent disease much better than they prevent infection. They will not eradicate pertussis, therefore, but in countries with very high coverage rates (>95%), the three to five yearly increase in disease rates affects fewer individuals and the resultant disease is less severe than in unvaccinated communities.
New Zealand epidemiology
Pertussis mortality in New Zealand - The estimated pertussis case fatality rate in New Zealand for the period 1970 to 1992 was 0.4 percent.
- This is comparable to reported case fatality rates from the UK and the US over a similar period.
- There were no deaths from pertussis in New Zealand between 1988 and 1995, one death in 1996, and since 1999 there has been one death each year up to 2004.
Pertussis morbidity in New Zealand - Pertussis morbidity in New Zealand has been described primarily using hospital discharge data. National passive surveillance data has been available since 1996, when pertussis became a notifiable disease.
- Comparison of notification and hospitalisation data from 1996 and 1997 demonstrates that fewer than 50 percent
of hospitalised cases are notified. - The three to four year periodicity of pertussis epidemics in New Zealand is similar to that seen in many other countries.
- The decrease in the pertussis hospitalisation rate that occurred following the introduction of mass immunisation has not been sustained.
Most recent epidemic - The most recent epidemic of pertussis started in April/May 2004 and continued into 2005. In 2004 there were 3489 cases of pertussis notified, a population rate of 93.4 cases per 100,000, and of these 1085 (31 percent) were laboratory confirmed.
- The highest rates of disease were reported from the South Island, except on the West Coast, and the rate was especially high in Southland, with a rate of 592 per 100,000. In the North Island, Waikato had high rates of disease. From the notification data in 2004, a total of 159 cases were hospitalised (3.4 percent).
- The highest rates of disease were in infants less than one year of age, with a rate of 327.5 per 100,000, although rates were high up to age 19 years. There were also many cases reported in adults.
- Among the notified cases, the population rates were higher in those of European ethnicity with a rate of 105 per 100,000, compared with 64 per 100,000 in Maori, 33 per 100,000 in Pacific peoples and 48 per 100,000 in those of ‘Other’ ethnicity. However, the highest rate of all groups was in Pacific infants under the age of one year, with a rate of 428 per 100,000.
- The hospitalisation rates were higher in Maori and Pacific infants during 2004. An Auckland study of infants found that delayed immunisation in infancy is a risk factor for infants being hospitalised with pertussis.
Prevention - Immunisation- Pertussis vaccines were initially developed in the 1940s.
- There are two types of pertussis vaccine commonly used internationally: whole cell pertussis vaccine and acellular vaccine. Both vaccines have similar efficacy but acellular vaccines cause significantly fewer adverse reactions than whole cell vaccines. Where feasible and available, acellular vaccines should be used in preference to whole cell vaccines.
- Acellular pertussis-containing vaccines have now replaced whole-cell vaccines in many countries, including New Zealand. There are a number of acellular pertussis vaccines, which contain 3 or more purified components of B. pertussis: pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN), and fimbrial antigens or agglutinogens.
Vaccine/s and Vaccination- Acellular pertussis vaccines with 3 or more antigens have similar efficacy to the best whole-cell vaccines.
- Acellular vaccines are significantly less reactogenic than whole-cell pertussis vaccines, causing fewer local reactions and less fever and other systemic reactions.
- Acellular vaccines are also immunogenic, safe and well tolerated in adults. The adult/adolescent formulation (dTap) contains lower concentrations of diphtheria, tetanus and pertussis antigens than infant and childhood diphtheria, tetanus and acellular pertussis (DTaP) vaccines.
- As protective efficacy of both natural infection and pertussis vaccine wanes over time, booster doses are required.
- There are a number of acellular pertussis vaccines that contain 3 or more purified components of B. pertussis; pertussis toxin (PT), filamentous haemagglutinin(FHA), pertactin and fimbrial antigens or agglutinogens.
- The vaccine is absorbed on an aluminium salt as an adjuvant.
- A number of combination vaccines are available with diphtheria, tetanus and/or Hepatitis B, Hib or polio components.
Prevention - Non Immunisation MethodsThere is almost no maternal protection passed to the newborn against pertussis, either in utero or via breastmilk. Antibiotics have no role in treating pertussis. However they are given to reduce transmission of the organism and may be given to all household and other close contacts of the patient. Identification and treatment of pertussis infection for women in the third trimester of pregnancy minimises the spread to non-immune infants in the first month of life. Cases should be excluded from school or daycare until fully recovered. Some countries recommend health care workers and/or daycare workers with confirmed pertussis infection be placed on sick leave until fully recovered.
Efficacy and EffectivenessAcellular - More than 80% through to 6 years of age, without boosting for some 3 or more component vaccines. Refer to manufacturer for efficacy data specific to preparation used.
- Immunity wanes 5-10 years after primary or booster immunisation.
- Studies on additional booster doses given during adolescence and adulthood suggest a protective efficacy of 32-99%.
Availability The publicly funded acellular pertussis vaccines for the New Zealand schedule are DTaP-IPV (Infanrix™) and DTaP-IPV-HepB/Hib (Infanrix™-hexa). In addition, a publicly funded combination vaccine of adult pertussis, diphtheria and tetanus, dTap (Boostrix®) is available. Adult diphtheria, tetanus and acellular pertussis vaccine, dTap (Boostrix®, GSK), is available for adult boosters but is not currently funded. Other acellular pertussis vaccines licensed for children in New Zealand include DTaP (Tripacel®, Aventis) and other combination vaccines, which include IPV, hepatitis B or Hib.
Comparison Chart | ANTIGENS (0.5 ml dose) | BOOSTRIX® (dTap) | INFANRIX™ (DTaP) | | Diptheria toxoid | 2.5 Lf U | 25 Lf U | | Tetanus toxoid | 5.0 Lf U | 10 Lf U | | Pertussis toxoid | 8.0 Mcg | 25 Mcg | | Filamentous haemaggluttin | 8.0 Mcg | 25 Mcg | | Pertactin | 2.5 Mcg | 8.0 Mcg |
Dosage and Administration
In New Zealand DTaP-IPV-HepB/Hib (Infanrix™-hexa), a combination vaccine, is given at six weeks, three months and five months of age. At four years of age DTaP-IPV (Infanrix™-IPV) the fourth dose, is given prior to school entry. dTap (Boostrix®) is given at eleven years of age. - There is considerable variation worldwide in the timing of the three primary doses.
- Booster doses are recommended around school entry age.
- A booster dose in adolescence is now recommended in some countries.
- The adolescent/adult formulation contains lower concentrations of pertussis toxoid than the child formulations.
- Immunisation is recommended for health professionals and staff of daycare centres. Boosters of dTap may be given at approximately 10 yearly intervals. Other adults who wish to receive a booster dTap are encouraged to do so.
- Administration is by intramuscular injection.
Indications and RecommendationsInfants and children - All infants should receive pertussis vaccine as a component of the primary course of vaccination in the first six months of life against diphtheria, tetanus, pertussis, IPV, hepatitis B and Hib which are recommended for all infants from 6 weeks of age, unless there is an absolute contraindication.
- The same brand of vaccine should be used for each of the 3 doses where possible. If it is not known which brand was used, vaccination should still be provided with an available brand.
- In view of the high morbidity and mortality associated with pertussis under the age of 6 months, receipt of the first dose of vaccine as soon as possible is important.
- If the primary course is interrupted, it should be resumed but not repeated; doses may be given as little as 28 days apart.
Adolescents and Adults - There are now acellular pertussis containing vaccines that are safe and immunogenic in adolescents and adults.
During outbreaks - Immunisation initiated after pertussis exposure does not protect from that exposure however during an outbreak efforts should be made to properly immunise children who have not completed a full vaccination course.
- An accelerated infant schedule may be indicated.
- There is no evidence that supplemental doses for fully immunised children are required.
- Supplemental immunisation of children who have immunologic or cardiopulmonary compromise may be considered if the benefits of vaccination are believed to outweigh the risks of adverse reactions.
Adverse EventsAcellular - Mild, local or systemic reactions are common (0.8-44%).
- Rare reactions which resolve spontaneously include:
- Convulsion with or without fever
- Persistent inconsolable screaming for 3 or more hours
- Hypotonic-hyporesponsive episode (HHE)
- Extensive circumferential limb swelling and redness
- Anaphylaxis (immediate treatment required)
Whole Cell - Mild, local or systemic reactions are common (13.7-62%).
- Severe reactions occur as per acellular pertussis vaccine with up to 10 times the frequency.
Contraindications- Anyone with encephalopathy without other cause, with onset within 7 days of prior to pertussis vaccination.*
- Anaphylactic reaction to a prior dose.
- Immunisation in individuals with an evolving neurological condition should be postponed until the condition is stabilised or given a diagnosis.
*Controversy exists about the association between pertussis and encephalopathy. Current evidence is inconclusive. No specific form of brain damage has been attributed to pertussis immunisation. Some experts believe there is a very rare association between pertussis immunisation and acute encephalopathy, while others deem it to be biologically plausible but unproven. This is the rationale for pertussis immunisation being contraindicated if encephalopathy develops within 7 days of immunisation and no other cause can be determined for its development. Risks vs benefitsDisease | Risks of disease | Risks of Vaccine | Pertussis – a highly contagious bacterial infection causing whooping cough and vomiting. | 90% risk of contracting pertussis for non-immune infants. 20% of all adults and adolescents may be infected at one time. 0.1-0.3% risk of permanent neurological damage for patients with paroxysmal cough.
Case fatality of 0.05% in hospitalised infants. | Mild local or systemic reactions (0.8-62%) Rare serious adverse events: Severe local reaction (0.8-8.0%) Convulsions (0.00007%)
Persistent screaming (<0.005%)
HHE (<0.003%) Anaphylaxis (<0.00001%) |
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