General Information
Pertussis, also known as 'whooping cough', is a highly infectious bacterial disease of the respiratory tract and is spread by droplet infection. Pertussis infection is caused by a gram-negative bacterium called Bordetella pertussis which is found in the back of the throat of an infected person. The incubation period is seven to ten days but the infectious period can be from seven days to three weeks after the onset of typical paroxysms.
Pertussis has the highest incidence in infants. School aged children are often the source of infection for younger siblings at home, however, infection also occurs in adolescents and adults. Morbidity and mortality are higher in females than males.
Photo: CDC
Clinical Symptoms
An irritating cough gradually becomes outbursts of coughing (paroxysms), usually within one to two weeks, and often lasts for two to three months ("one-hundred-day cough"). Not all have the characteristic 'whoop', particularly in young infants, and cough spasms may be followed by a periods of vomiting. Symptoms may start similar to a common cold, progressing to coughing and choking spells. Severe complications and deaths occur mostly in infants under six months of age. Serious illness is less common in older children and adults (1 in 15,000 - 21,000), however, they have the potential to transmit infection to vulnerable babies.
Epidemiology
Before the introduction of pertussis immunisation in the 1950s, the average annual number of notifications in England and Wales exceeded 100,000. In 1972, when vaccine acceptance was over 80%, there were only 2069 notifications of pertussis. Public anxiety about the safety and efficacy of the vaccine, following a report published which suggested the vaccine was a common link between a group of children with brain damage, saw immunisation coverage drop to 30% in 1975 resulting in major epidemics in 1977/79 and 1981/83. As a result, there were more than 200,000 extra notifications and 100 deaths in 1970s and 1980s. Vaccine coverage steadily increased over the next decade as public and professional confidence in the vaccine was restored, reaching 94% in 1995, at which level it has remained. Correspondingly, notifications decreased dramatically during this period with 2000 being the lowest on record. The Health Protection Agency (HPA) initiated a programme of enhanced surveillance to monitor the number of cases of whooping cough and vaccine efficacy in 1994.
However, despite a high vaccination uptake, the burden of pertussis in England and Wales remained highest in children too young to be fully protected.
Following a detailed study of pertussis in infants on paediatric intensive care units (PICUs) and mathematical modelling by the HPA, in November 2001, a pre-school booster dose of pertussis vaccine (given between 3-5 years of age) was added to the routine immunisation schedule with the aim of reducing illness in older age groups thereby reducing transmission of pertussis to babies too young to be fully protected.
Diagnosis
In England and Wales, whooping cough is statutorily notifiable whereby a diagnosis is usually made on clinical grounds without the requirement for laboratory confirmation. Notifications provide timely data relating to trends over time and by age.
Diagnosis can be confirmed through isolation of the B. pertussis organism through culture. However culture lacks sensitivity and since 2001, enhanced diagnostic methods, such as PCR and serological testing, have been made available by the HPA. These more sensitive methods have increased case ascertainment, particularly in adults. View the latest epidemiological data and information on laboratory testing services.
Classic (severe) pertussis, as defined by the World Health Organization (WHO), consists of at least 21 days of cough illness with paroxysms, associated whoops or post-tussis vomiting, and culture confirmation. Mild pertussis is any laboratory-confirmed pertussis disease that does not meet the criteria for classic disease.
Prevention and treatment
Acellular pertussis vaccine is given in the primary course with diphtheria, tetanus, polio and Hib, as DTaP/IPV/Hib, given at aged 2, 3, & 4 months of age. A further booster dose with acellular pertussis, given as dTaP-IPV, is given with the preschool boosters between the ages of 3 and 5.
Children and adults can catch pertussis even if they were vaccinated in the past because vaccine immunity wanes over time. However, since the introduction of pertussis booster at pre-school in November 2001 morbidity has been at historically low levels in infants too young to receive the vaccine as well as in age groups targeted for immunisation.
Pertussis commonly lasts 6-8 weeks even when treated with antibiotics, with severity of symptoms related to age. The most severe infections are usually in infants, and over 50% are hospitalised as a result. Morbidity and mortality is greatest in those aged less than 6 months of age. Close contacts of pertussis cases and who are particularly vulnerable, unvaccinated, partially vaccinated or less than five years of age are given erythromycin treatment or prophylaxis (Dohia H, Miller E, Epidemiol Infect 1998; 143-49). Although the evidence base for using newer macrolides antibiotics such as azithromycin and clarythromicin is less extensive than erythromycin these are likely to be suitable alternatives for treatment and prophylaxis and are better tolerated.
Frequently asked questions
Does the pertussis vaccine cause brain damage?
In 1974 a paper was published suggesting a link between the whooping cough vaccine and brain damage. Because of this concern, the number of children receiving the vaccine fell. As a consequence, the number of cases and deaths from the disease rose. Subsequent research shows that, if there is a long-term risk of brain damage from the vaccine, it is rare, whereas the disease itself is known to cause brain damage and death.
What is acellular whooping cough vaccine?
The traditional 'whole-cell' vaccine is made from the whole germ, whereas the 'acellular' vaccine only contains parts of it. The whole-cell vaccines tend to provide better protection. At 2, 3 and 4 months there is little difference in side effects between whole-cell and acellular pertussis vaccines.
