**1. Introduction**

Whopping cough is mentioned in medical literature since 1540, in the pre-vaccine era, when the incidence of the disease ranged from 100 to 200 cases per 100,000 people [1, 2].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This same incidence is observed nowadays in many developing countries and also in some high-income countries among children under 1 year of age. The vaccine age begins in the 1940s with the whole-cell pertussis vaccines (wP vaccines) and in 1992 with acellular pertussis vaccines (aP vaccines) in developed countries, with a marked decrease in the number of sick individuals as well as in the number of hospitalizations. Despite this, there has been an increase in the incidence and deaths due to pertussis in infants fewer than 6 months of age between 1980 and 2010 in the USA, in Europe, and in many other countries [1–5]. Whooping cough is a highly infectious disease caused by *Bordetella pertussis* and, more rarely, by *Bordetella parapertussis*, *B. bronchiseptica*, or *B. holmesii*. It is the most ill-controlled vaccine-preventable bacterial disease in countries with high vaccination coverage, in which disease peaks occur every 3–5 years. Although routine childhood vaccination has produced a substantial reduction in the number of cases, it continues to cause high morbidity and mortality in children in countries across the globe [6–8]. In developed countries with pertussis vaccination coverage above 90–95%, such as the USA, the UK, several European countries, and Australia, pertussis has manifested in children under 6 months of age when they have not yet completed their primary series and in adolescents and adults who lost their immunity induced by the vaccine (the last booster is given at the age of 5 years). Young infants present atypical and potentially serious conditions, with about 50% of the cases leading to hospitalizations and often even to death, while adolescents and adults also present atypical but mild symptomatology, and as a result, the individual is often mistakenly diagnosed with other infections of the upper respiratory tract [2, 3, 9, 10]. The causes of the decreasing immunity to pertussis are varied: from the primary vaccine failure due to bacterial adaptations to the failure of the vaccine to eliminate the bacteria from the carriers' organism and thereby prevent transmission to the dropping of protective antibodies. The duration of protection of the acellular vaccines is approximately 3 years, with 85% efficacy, and the risk of contracting the disease increases by 1.33 times each year after the last dose of the vaccine. Therefore, the vaccine protects against the disease, but not against bacterial colonization and its consequent transmission. Loss of vaccine-derived protection over time and increased circulation of *B. pertussis* lead to increased susceptibility of adolescents and adults. As a result, whooping cough is often reported as a cause of persistent cough in adolescents and adults [6, 11–14]. The variation in the notification of the age group affected by pertussis can be explained in part by a growing recognition of the less typical manifestations of the disease in adolescents and adults and by severe cases in young infants. It can also be explained by the development of more sensitive laboratory tests and by a more sensitive and extended healthcare surveillance to cover all life periods [15–17]. Outbreaks in areas of high vaccination coverage demand a review of vaccination strategies. It is necessary to take into account adolescent and adult transmitters, as well as health professionals and pregnant women. In order to better assess changes in epidemiology over time and to optimize disease control, it is important to improve whooping cough surveillance, from clinical recognition of the disease to laboratory diagnosis [18]. In 2013, according to the WHO estimates, pertussis caused about 63,000 deaths in children under 5 years of age, although there is considerable uncertainty about these estimates in view of the scarcity of reliable

surveillance data, especially in developing countries [16, 19]. In 2014, pertussis global vaccination coverage was estimated at 86%, considering adherence to the vaccine primary series of three doses. A change in age distribution of the disease for older children and certain age groups (adolescents and young adults) has been reported in recent years in some high-income countries, in particular where aP vaccines have replaced wP vaccines in primary series and booster doses [15, 16]. High vaccination coverage needs to be maintained in order to ensure protection of newborns and young infants, the two groups most likely to show the most severe symptoms and who have not yet started or did not complete their primary series of vaccines. The recent shortage of pertussis vaccine in Europe and elsewhere represents a considerable challenge for maintaining such coverage [18]. It is estimated that the incidence of whooping cough is actually 6–9 times higher than the reported cases, which in 2016, according to the WHO, were 139,535 cases. The unfamiliarity with the disease and its incorrect diagnosis seem to be particularly common among adolescents and adults, due to its atypical clinical presentation. Persistent cough is often the only sign of the disease, and this signal can be attributed to many other conditions and is generally not correlated to whooping cough; so, diagnostic is not performed. On the other hand, the search for specific antibodies in respiratory secretions of patients with chronic cough usually comes as negative. Only serology will identify the cases, and, in turn, serology may not be able to differentiate current active cases from recent cases. The actual incidence of pertussis remains unknown, because data collection varies greatly between countries, which affect the interpretation of trends. There are also variations in the diagnostic methods for laboratory confirmation, in the definition of a case of pertussis and the clinical diagnosis itself [18, 20, 21]. In addition to all the difficulties of data collection, there is still the issue of high contagiousness of the disease, even among vaccinated individuals. A study carried out on vaccinated children, aged 1–5 years, in a preschool class, who had contact with a pertussis case, observed attack rates approaching 50%. This shows the importance of diagnostic investigations even in vaccinated children. The clinical condition will also highly depend on the history of each child, which emphasizes the

Clinical Experiences in Pertussis in a Population with High Vaccination Rate

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There is no consensus as to why the number of pertussis cases has increased in countries with high vaccination coverage. The reasons range from improvements in diagnosis, earlier diagnosis, and more accurate surveillance. These changes have led to an increase in the number of reported cases, but there is also evidence of increased circulation of the bacteria in the population. There are several other explanations for increased epidemics: changes in circulating pertussis virulence, vaccine failure against new bacteria, vaccine failure to block transmission of infection, decreased adherence to vaccination, rapid loss of immunity in adolescents and adults due to the vaccine or due to the disease itself over time, making the vaccinated individuals susceptible, and also the increase of susceptible individuals in the

seriousness of the matter [22].

population [10, 17, 23–25].

**2. Whooping cough: current situation**

surveillance data, especially in developing countries [16, 19]. In 2014, pertussis global vaccination coverage was estimated at 86%, considering adherence to the vaccine primary series of three doses. A change in age distribution of the disease for older children and certain age groups (adolescents and young adults) has been reported in recent years in some high-income countries, in particular where aP vaccines have replaced wP vaccines in primary series and booster doses [15, 16]. High vaccination coverage needs to be maintained in order to ensure protection of newborns and young infants, the two groups most likely to show the most severe symptoms and who have not yet started or did not complete their primary series of vaccines. The recent shortage of pertussis vaccine in Europe and elsewhere represents a considerable challenge for maintaining such coverage [18]. It is estimated that the incidence of whooping cough is actually 6–9 times higher than the reported cases, which in 2016, according to the WHO, were 139,535 cases. The unfamiliarity with the disease and its incorrect diagnosis seem to be particularly common among adolescents and adults, due to its atypical clinical presentation. Persistent cough is often the only sign of the disease, and this signal can be attributed to many other conditions and is generally not correlated to whooping cough; so, diagnostic is not performed. On the other hand, the search for specific antibodies in respiratory secretions of patients with chronic cough usually comes as negative. Only serology will identify the cases, and, in turn, serology may not be able to differentiate current active cases from recent cases. The actual incidence of pertussis remains unknown, because data collection varies greatly between countries, which affect the interpretation of trends. There are also variations in the diagnostic methods for laboratory confirmation, in the definition of a case of pertussis and the clinical diagnosis itself [18, 20, 21]. In addition to all the difficulties of data collection, there is still the issue of high contagiousness of the disease, even among vaccinated individuals. A study carried out on vaccinated children, aged 1–5 years, in a preschool class, who had contact with a pertussis case, observed attack rates approaching 50%. This shows the importance of diagnostic investigations even in vaccinated children. The clinical condition will also highly depend on the history of each child, which emphasizes the seriousness of the matter [22].
