**1. Introduction**

Whooping cough or pertussis is a respiratory disease that though preventable by vaccination remains an important health problem not only for infants but also for adolescents and adults [1, 2]. By definition, the etiologic agent responsible for this disease is the Gram-negative bacterium named *Bordetella pertussis*. However, pertussis-like symptoms can be caused by several other *Bordetella* species, including *B. parapertussis*, *B. bronchiseptica*, and *B. holmesii* [3–8]. The

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disease usually starts with cold-like symptoms and irritating cough that gradually becomes paroxysmal. Paroxysms are characterized by repeated violent coughs; each series of paroxysm has many coughs without intervening inhalation and can be followed by the characteristic inspiratory whoop. Complications are frequent: about half of the babies younger than 1-year old who get pertussis need care in the hospital. Of those babies with pertussis who are treated in the hospital, about 1 out of 4 (25%) get pneumonia, 1 out of 100 (1%) will have convulsions, 1 out of 300 (0.3%) will have encephalopathy, and 1 out of 100 (1%) will die.

delays in the primary doses reduces infant incidences by approximately 20% [22]. In the same way, the simultaneous reduction of delays and increased coverage lead to a significant improvement in disease control [22] for those regions where the administration of vaccines

Update on Epidemiology, Diagnosis, and Treatment of Pertussis

http://dx.doi.org/10.5772/intechopen.72847

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The maximal risk of pertussis infection and severe morbidity takes place before infants are old enough to have received the primary series of vaccination. [23–25]. In recent years, waning immunity seems to be the main cause for pertussis in adults and adolescents [26–28], and for this reason, these persons constitute a significant reservoir of infection. Evidence from studies of infant pertussis cases indicates that household contacts and carriers are frequently the source of infection, with parents identified as the cause for more than 50% of cases [29]. There has also been a case report documenting nosocomial infection in young infants acquired from

Despite a long-standing vaccination program, pertussis remains highly prevalent in many countries [15]. Pertussis is the least well controlled of all vaccine-preventable diseases, and epidemics occur every 3–5 years. During the last decades, multiple epidemics of pertussis took place in many countries including those with high vaccination coverage [14, 15]. In the United States, where aP is used for all vaccination doses since 1996, in 2010–2012, the incidence rate in infants with less than 1 year duplicated those in 2002 (125 vs. 60 per 100,000 inhabitants), and incidence rates were very high not only in infants but also in 7–10-year-old children and adolescents (13–14 years) http://www.cdc.gov/pertussis/outbreaks/trends.html. In 2014, 32,971 cases of pertussis were reported to the Centers for Disease Control and Prevention (CDC). This represents a 15% increase compared to the 28,639 cases reported during 2013. During 2015, a decrease in the number of pertussis cases was reported: 20,762 cases in 2015 compared to 32,971 cases reported during 2014. As in previous years, in 2015, the incidence rate of pertussis in infants exceeded that of all the other age groups. However, the incidence

Another industrialized country experiencing a notable outbreak is the UK, where, in 2012, 14 infant deaths were reported (Public Health England; cf. https://www.gov.uk/government/

In Australia, the highest annual incidence of notifications (173 cases per 100,000 population) was reported in 2011, with 38,732 notified cases. In the epidemic period 2008–2011, an increase in the reporting of pertussis in children between 3 and 9 years of age was detected. On the other hand, notifications in adolescents and adults decreased compared to previous epidemic periods. In this country, there have been a number of changes introduced to the vaccination schedule over time in an attempt to improve control of pertussis. In this way, acellular pertussis vaccine replaced wP for booster doses in 1997 and for all doses from 1999. In 2003, the aP booster dose at 18 months of age was removed, shifting the first booster dose

publications/whooping-cough-pertussis-statistics, accessed October 2017).

was previously deferred for long periods of time.

rates in adolescents aged 13–16 years were also high.

**2. Epidemiology**

health-care workers [30, 31].

to 4 years of age.

The best control strategy to prevent pertussis is vaccination. Currently, two types of vaccines against pertussis are in use: the whole-cell vaccines (wP) composed of whole, inactivated bacteria, and the acellular vaccines (aP) consist of purified *B. pertussis* immunogens. With the massive use of the first developed vaccine against the disease, the wP, in the 1950s, the incidence and mortality associated with pertussis fell to very low levels. Reports on safety concerns in the 1970s, however, cast doubt on the wP vaccines' value since they were associated not only with side effects at the injection site but also with serious systemic reactions [9, 10]. These drawbacks contributed to reducing pertussis vaccine acceptance in different countries [10, 11]. The widespread apprehension about wP prompted the development of acellular vaccines containing purified antigenic protein components of *B. pertussis* (two, three, or five immunogens) [12, 13]. Though finally there is no evidence to suggest that wP vaccines cause severe adverse reactions such as brain damage or severe neurological disorder, the aP vaccines are more accepted, especially in industrialized countries where they have gradually superseded the wP formulations. Currently, most of the countries of the EU and the USA use only aP vaccines. The aP formulations restored people's confidence in pertussiscontaining vaccines, and infection appeared controlled for several years. Notwithstanding, during the last two decades, the epidemiology of pertussis has changed [14, 15] with several major outbreaks occurring, the incidence of which not only indicated a waning immunity but also demonstrated that the wP vaccines gave children a more lasting immunity than aP [16–18]. Furthermore, the risk of pertussis was increased in schoolchildren, and adolescents vaccinated exclusively with aP compared to those receiving only one wP dose [18, 19]. This difference could result from the weaker immune response induced by aP vaccines characterized mainly by Th2 profiles [20]. In 2015, the Strategic Advisory Group of Experts on immunization expressed concerns regarding the resurgence of pertussis in some industrialized countries despite high aP-vaccine coverage [21]. The switch from wP to aP for primary infant immunization was proposed as at least partially responsible for that resurgence. The World Health Organization (WHO), therefore, recommended considering the switch only if, in the national immunization schedules, large numbers of doses including several boosters could be assured. Countries currently using aP vaccines may continue using them but should consider the need for additional booster doses and strategies to prevent early childhood mortality upon pertussis resurgence.

Besides these recommendations and in order to control the disease in countries that use cellular, acellular, or even mixed vaccine schedules, it is important not only to achieve coverage levels above 95% but also to avoid delays in the application of vaccines [22]. By means of a mathematical model, it was reported that strategies that avoid delays in vaccination have a relevant impact on infant incidences' reduction. It was estimated that the elimination of delays in the primary doses reduces infant incidences by approximately 20% [22]. In the same way, the simultaneous reduction of delays and increased coverage lead to a significant improvement in disease control [22] for those regions where the administration of vaccines was previously deferred for long periods of time.
