Fact file - Prevention, diagnosis and management of pertussis
- Published: 04 December 2006 15:58
- Last Updated: 20 February 2007 16:18
VOL: 102, ISSUE: 46, PAGE NO: 42
Helen Bedford, FRCPCH, PhD, RHV, is senior lecturer in children?s health, Centre for Paediatric Epidemiology and Biostatistics Institute of Child Health, London; David Elliman, FRCPCH, FFPH, FRCP, is consultant in community child health, Islington PCT and Great Ormond Street Hospital Children?s Population Health Unit, Great Ormond Street Hospital for Children, London
Pertussis, commonly referred to as whooping cough, is a highly infectious respiratory disease caused by the bacterium Bordatella pertussis and is spread by droplets. The incubation period is between 5 and 21 days although usually less than 10 days (Richardson et al, 2001). Before the cough develops there is usually a non-specific cold-like illness (prodromal illness). Pertussis is infectious from the start of this prodromal phase to three weeks after the cough starts (Crowcroft and Pebody, 2006). Pertussis, commonly referred to as whooping cough, is a highly infectious respiratory disease caused by the bacterium Bordatella pertussisand is spread by droplets. The incubation period is between 5 and 21 days although usually less than 10 days (Richardson et al, 2001). Before the cough develops there is usually a non-specific cold-like illness (prodromal illness). Pertussis is infectious from the start of this prodromal phase to three weeks after the cough starts (Crowcroft and Pebody, 2006). Classically, the coughing comes in paroxysms followed by a whoop and/or vomiting. However, one of the complicating factors in diagnosis is that in infants, older children and adults the whoop is often not present and the illness may simply present as a long-lasting cough. Young babies may present atypically, with apnoea or even sudden death (Crowcroft and Pebody, 2006). The coughing stage lasts 2-6 weeks and may only subside gradually, so the whole illness may last over three months. Complications are most likely to occur in young infants (under six months) and include pneumonia, failure to thrive, seizures and brain damage resulting from hypoxia. It is estimated that there are at least nine deaths a year from pertussis, mostly in babies aged under six months (Crowcroft et al, 2002). Adults play a significant role in transmission. In Bisgard et al's (2004) study, over 70% of infants were reported to have been infected by their mother or another family member, most of whom were aged 20 years or older. IncidenceBefore vaccination, pertussis was most commonly reported among children under 10 years old and particularly among those aged between three and six years, with approximately 120,000 cases reported each year (Department of Health, 2006). Notifications are lower now than at any time since surveillance began (Health Protection Agency, 2006) but this infection remains a real danger for young babies. It is difficult to provide accurate figures on the incidence of pertussis as there is evidence that it is both underdiagnosed and under-reported. Diagnosis is usually based on clinical signs. Pernasal cultures (cultures taken using a special swab passed through the nose) are often negative. The use of polymerase chain reaction (PCR) and/or serology is more accurate. However, PCR is not always available and serology tests may be difficult to interpret if the patient has already been immunised (Fry et al, 2004). Taking blood samples from young children for these tests can be difficult. There is evidence that unexplained prolonged cough in adults and adolescents may be due to pertussis (Strebel et al, 2001). Recently, Harnden et al (2006) showed that almost 40% of children aged 5-16 years who attended their GP with a cough lasting 14 days or more had serological evidence that this was whooping cough. Most of the children had been given a full primary course of pertussis immunisation but all were too old to have been eligible for the preschool booster of pertussis, introduced in 2001 (Chief Medical Officer, 2001). This study confirms that immunity following immunisation wanes and that there is a need for a preschool booster. Crowcroft et al (2002) showed that deaths due to pertussis are under-reported and in the period 1994-1999 there were probably nine deaths annually, over twice the number reported. The authors commented that this may still be an underestimate of actual numbers. TreatmentTreatment is mainly supportive and looking after a child with pertussis can be very distressing. Erythromycin or some of the newer macrolide antibiotics, if given early enough, may make a difference to the course of the illness and reduce infectivity but usually diagnosis is too late for such treatments (Altunaiji et al, 2005). VaccinationVaccines were first developed in the early 20th century. The first was licensed in the USA in 1914, but it was not widely used until 30 years later. The vaccine was introduced on a large scale in the UK in 1942 and by 1951 it was estimated that over 80% of infants in England and Wales were being offered immunisation (Griffith, 1981). It did not become part of the national programme until 1957. These initial vaccines were prepared from whole bacteria, and were known as ?whole cell' vaccines. Trials by the Medical Research Council in the early 1950s had shown the vaccine was highly effective and, following its introduction, there was a significant reduction in cases of pertussis and deaths from the disease. More recent studies have shown that most whole cell vaccines have an efficacy of over 90% against typical disease (Brown et al, 1997). Immunity is known to wane after vaccination and after an episode of whooping cough infection although it is not clear which declines faster (Crowcroft and Pebody, 2006). There have been reports of serious adverse events following vaccination but little evidence of a causal connection. In the mid-1970s concerns over safety became widespread following publication of a paper in a paediatric journal. The paper described 36 children seen at Great Ormond Street Hospital over a period of 11 years who were believed to have developed neurological complications following pertussis vaccination (Kulenkampff et al, 1974). This became the subject of a TV documentary in March 1974. Within days mothers were withdrawing consent for pertussis vaccine and over the following years the issue continued to attract attention in the media (McKinnon, 1979). At the time, both diphtheria and tetanus (DT) and diphtheria, tetanus and pertussis (DTP) vaccines were equally available and many parents, often on the advice of doctors, opted to omit the pertussis component (Peckham et al, 1989). Uptake of pertussis vaccine fell to a national level of about 30% with uptake as low as 9% in some areas. There were two major epidemics of pertussis with an increase in deaths (Gangarosa et al, 1998). A large case control study was set up in the UK - the National Childhood Encephalopathy Study (NCES). This showed that there may be a risk of permanent neurological problems following the vaccine at a rate of approximately one for every 310,000 injections (Alderslade et al, 1981). Based on average caseloads, it was calculated that this amounted to one instance every 1,500 years in a general practice with four GPs. This research was re-examined in a court case in the UK and the judge concluded that there was no conclusive evidence that the vaccine causes permanent neurological problems (Brahams, 1988). The Institute of Medicine in the USA concluded in 1994 that the balance of evidence is consistent with a causal relation between DTP and the forms of chronic nervous system dysfunction described in the NCES in children who experienced a serious acute neurological illness within seven days of receiving the DTP vaccine. This serious acute neurological response to DTP is a rare event (Stratton et al, 1994) and subsequent research has supported the findings of the UK courts (Gale et al, 1994). Acellular vaccines Over the years, public and professional confidence was restored and uptake of pertussis vaccine in the UK rose and is now 94% (Health Protection Agency, 2005). As a result, rates of the disease have fallen. In a quest for safer vaccines, research has been conducted into acellular vaccines. These contain only a limited number (one to five) of the components of the bacteria, unlike the whole cell vaccine which has been estimated to contain approximately 3,000. Studies have consistently found that the milder adverse events associated with immunisations, such as local reactions and pyrexia, are less common after the use of acellular vaccines (Brown et al, 1997). The position is less clear with respect to the more severe adverse events but the balance of the evidence is that they are also probably less common, especially in children (Brown et al, 1997). As a generalisation, the more components an acellular vaccine contains, the higher the protection it gives, with the five-component vaccine being the most efficacious. This is extremely important for the primary course of immunisation, where only the five-component vaccine should be used. As a booster, the three and five-component vaccines are equally effective. Estimates vary about the speed of decline of vaccine-acquired immunity but it is enough to justify a preschool booster. Many countries also give a booster in the second year of life. One problem with acellular vaccines is their effect on the response to other vaccines given at the same time. The whole cell vaccine acted as an adjuvant and it enhanced the immunogenicity (the ability of a vaccine to generate an immune response) of some vaccines mixed with it. The acellular vaccines do not have this effect. In fact, one of the acellular vaccines containing three components, when mixed with Hib vaccine, significantly reduces the response of the Hib vaccines and increases the number of vaccine failures (disease developing despite immunisation). This effect is not seen with the five-component vaccine, which is another of its advantages over vaccines with fewer components (Mills et al, 1998). ContraindicationsContraindications to vaccination have become more evidence based and less extensive. The contraindications to acellular pertussis vaccines are no different from those to any other killed vaccine - an anaphylactic reaction to a previous dose or constituent of the vaccine. Children with a febrile illness or systemic upset should be immunised when they are better. Those with an evolving neurological illness should have vaccination postponed until the condition has stabilised. Immunisation policyPertussis vaccine is recommended in the UK at two, three and four months, with a preschool booster usually three years after the last dose of the primary course. When the primary course has been completed late, the booster dose may be given after a shorter interval, as long as at least one year has elapsed. The vaccine is given in a combination product with other primary vaccines and is not available separately. It is not normally recommended for those over 10 years old. The UKschedule from September 2006 is outlined in Box 1. Thiomersal preservativesThiomersal (a mercury-containing preservative) is used in the manufacture of whole cell vaccines but not for acellular vaccines. There is no evidence of harm but, based on the precautionary principle, many regulatory bodies have recommended that, where possible, vaccines free from thiomersal are used (Centers for Disease Control, 1999). The futureWith increasing concern about the pool of pertussis in adults, it is possible that the UK will follow other countries and add acellular pertussis vaccine to the school leavers' booster (Southern et al, 2005). It is important that as many children as possible receive the vaccine to ensure some protection for those too young to receive the vaccine. Parents need accurate advice from health professionals about the benefits of vaccination (Box 2). Box 1. Vaccination schedule from September 2006| Age at vaccination | Vaccine |
| Two months | DTaP/IPV/Hib + pneumococcal vaccine |
| Three months | DTaP/IPV/Hib + MenC vaccine |
| Four months | DTaP/IPV/Hib + MenC + pneumococcal vaccine |
| 12 months | Hib/MenC |
| 13 months | MMR + pneumococcal vaccine |
| Three-and-a-half to five years | DTaP/IPV + MMR vaccine |
| 13-16 years | Td/IPV
|
- Whooping cough is much less common since vaccination
- Although the pertussis vaccine is very effective, its protection wanes and it
is important that children have a
preschool booster - Young babies are most severely affected
by whooping cough - Young babies depend on herd immunity for their protection before they are old enough to be vaccinated
- Older children and adults can transmit whooping cough to young babies
- Older children and adults with whooping cough may present with a persistent cough
- Seek medical advice for a child who has a cough lasting more than two weeks, even if the child has been immunised
Department of Health (2006) Pertussis. Online resource. www.dh.gov.uk/assetRoot/04/13/79/23/04137923.pdf.
Fry, N.K. et al(2004)Laboratory diagnosis of pertussis infections: the role of PCR and serology. Journal of Medical Microbiology; 53: 6, 519-525.
Gale, J.L. et al (1994) Risk of serious acute neurological illness after immunization with diphtheria-tetanus-pertussis vaccine. A population-based case-control study. Journal of The American Medical Association; 271, 1: 37-41.
Gangarosa, E.J. et al (1998) Impact of anti-vaccine movements on pertussis control: the untold story. Lancet; 351: 356-361.
Griffith, A.H. (1981)Medicine and the media-vaccination against whooping cough. Journal of Biological Standardisation; 9: 4, 475-782.
Harnden, A. et al (2006) Whooping cough in school-age children with persistent cough: prospective cohort study in primary care. British Medical Journal; 333: 174-177.
Health Protection Agency (2006) Pertussis. Notifications, England and Wales, by Age Group, 1982-2005.www.hpa.org.uk/infections/topics_az/whoopingcough/data_not_age.htm.
Health Protection Agency (2005) Annual Cover Report 2004-2005. www.hpa.org.uk/infections/topics_az/vaccination/AnnCOVER2005A.pdf.
Kulenkampff, M. et al (1974) Neurological complications of pertussis inoculation. Archives of Disease in Childhood; 49: 1, 46-49.
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