Summary

Bordetella pertussis infection is endemic and continues to present a significant public health challenge in all age groups, particularly in young infants, even in countries with high vaccination coverage. It is therefore important to explore methods of preventing B. pertussis infection and disease in all age groups and transmission of infection to vulnerable young infants. Reliable and consistent data on the economic burden of pertussis are required to evaluate the potential cost effectiveness of wider immunization strategies. Currently the reliability of burden data is confounded by the difficulties in identifying the disease and the limitation of available data to developed countries only. The 3 articles in this section of the publication have reviewed our current understanding of the health and economic burden of pertussis disease.1–3 HEALTH BURDEN IN INFANTS AND CHILDREN Despite widespread immunization programs, pertussis is still one of the most common vaccine-preventable diseases in industrialized countries. Infants, particularly those younger than 6 months of age, who are unimmunized or incompletely immunized, are at the greatest risk of infection and experience the greatest disease burden and mortality from pertussis disease.4–6 The reported infant mortality rate attributed to pertussis may be underestimated, with pertussis disease being misdiagnosed as other respiratory illnesses or sudden infant death syndrome.7–11 Infants are susceptible to serious pertussis-related complications, such as pneumonia, seizures and encephalopathy, which often require hospitalization.12,13 Consequently the rate of hospitalization is higher for infants, particularly those who have not been fully immunized, than for older patients. The impact on parents caring for a child with pertussis disease is considerable. Parents suffer from fears for the life and health of their child and from serious loss of sleep.14,15 Moreover caring for a child with pertussis disease is likely to have an economic impact, because parents either lose workdays to care for their ill child or are less productive at work.16 HEALTH BURDEN IN ADOLESCENTS AND ADULTS It is a common misconception that pertussis disease does not occur or is only a mild illness in adolescents and adults. Although the incidence of pertussis disease is generally highest in infants, the proportion of cases reported to the Centers for Disease Control and Prevention among persons 10 years of age or older increased from 15% during the late 1970s to 49% during the late 1990s.4,17 As is the case for infants, the incidence of pertussis in adolescents and adults is likely underestimated because of a series of diagnostic issues: (1) a prolonged, nondistinctive cough may be the only clinical feature in adolescents and adults, who may or may not seek medical care; (2) if they do seek care, their illness is often misdiagnosed because of low awareness of the disease in these age groups18,19; (3) when pertussis is considered as a diagnostic possibility, it is often not confirmed because the available diagnostic tests are inadequate.18,20,21 The clinical manifestations of pertussis disease in adolescents and adults are often different from those in infants, ranging from mild cough to severe, persistent cough. However, the literature indicates that 21–86% of adults have symptoms more typical to those of infants, such as paroxysmal cough, whoop and posttussive vomiting.22–26 The duration of these symptoms, along with other manifestations (eg, sleep disturbance and weight loss), can have a serious impact on the economic burden of the disease by reducing productivity and attendance at work. In addition, pertussis-related complications and hospitalization occur fairly frequently among adolescents and adults, especially in the elderly. Death from pertussis, however, is generally rare beyond the age of 10 years.27,28 Recognition of pertussis infection in older age groups is vital because adolescents and adults may serve as vectors of B. pertussis infection for unimmunized or incompletely immunized infants.29–37 Because of the considerable health burden in all age groups, there is a need for improved adolescent and adult immunization programs to prevent transmission of B. pertussis infection to vulnerable infants. ECONOMIC BURDEN OF PERTUSSIS The lack of reliable and consistent data makes it difficult to evaluate the true economic burden of pertussis disease and the cost effectiveness of immunization strategies. However, current disease burden data suggest that the direct and indirect costs associated with pertussis are significant. Direct costs of pertussis disease vary according to age (being highest in infants) and are heavily dependent upon the need for hospitalization to treat pertussis-related complications. In a US study, the direct costs of pertussis disease were estimated to be US $2822 (€2302) per case for infants (younger than 24 months old) and US $181 (€148) per case for adults (19 years of age or older).16 According to a German study, an uncomplicated case of pertussis disease is estimated to produce direct costs of €110 (US $135), whereas a case that requires hospitalization because of encephalopathy, for example, is estimated to increase direct costs alone to €5170 (US $6337).38 The indirect costs of pertussis illness are also considerable. Parents experience reduced work productivity or absence from work both because they are caring for a sick child and because the parents may acquire pertussis and have a long recovery period. The collated data indicate that the indirect costs contribute as much as 73% of the total cost per case.16 Studies performed to date on the cost effectiveness of immunization strategies have been limited mainly to childhood immunization; cost effectiveness analyses for immunization of older age groups are scarcer and results are inconsistent. This is mainly because models rely heavily on assumptions for several key inputs in terms of epidemiology, economics and demography.3 Despite the uncertainty, cost effectiveness analyses have shown there to be potential health and economic benefits if high coverage levels can be achieved with acellular vaccines. Such analyses may help to inform decisions about expanding immunization against pertussis, by describing conditions for favorable results and quantifying the impact of uncertainty. CONCLUSION It is evident that pertussis disease poses a considerable burden not only to infants but also to adolescents and adults. Because older age groups can serve as vectors of B. pertussis infection, the disease burden in this group also impacts on infantile incidence. This could be reduced by immunizing older individuals, whose immunity to infection has waned. This approach has already been implemented in Australia, Austria, Canada, France and Germany, where adolescents are immunized against pertussis.39–41 Austria and Canada also have recommendations for adult immunization. Cost effectiveness studies of possible immunization strategies will help to determine which strategies are most appropriate for each country. Meanwhile more reliable, global economic data are required to determine the cost effectiveness of new immunization strategies more accurately, to help support decisions to implement wider immunization against pertussis.

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