**4. Diagnosis**

Outbreaks were also detected in countries where wP vaccines were used. For example, in Argentina, where wP is used for primary series of three doses at 2, 4, and 6 months of age followed by two boosters at 18 months and 6 years old, the number of pertussis reported cases has increased steadily since 2002. In fact, in 2011, reported cases were four times higher than those detected in 2006 (4.1 vs. 16 per 100,000 inhabitants) [32] and 76 deaths were reported in children under 1 year (www.snvs.msal.gov.ar, [32]. Because of this epidemiological situation during 2009, the Ministry of Health recommended vaccination with aP for children at age 11 and for health-care workers in contact with infants under 12 months of age. In 2011, the Argentinean Ministry of Health recommended aP vaccination for household contacts of very-low-birth-weight infants (<1500 g); in 2012, they also offered immunization to all pregnant women after 20 weeks of gestation. Finally, in 2013, the national calendar included the maternal immunization against pertussis during a single pregnancy for each woman, while,

Brazil, other country that uses wP for primary series, reported cases of pertussis from 2007 to 2014 [33]. The annual distribution of confirmed cases demonstrated a significant increase in incidence rate since 2012. Of the 80,068 suspected cases, 32% were confirmed by various criteria. The majority of confirmed cases occurred in infants who were less than 2 months (34.5%) and in infants aged 3–6 months (22.4%). Only 8% of the total confirmed cases was reported in adults >21 years. From the total confirmed cases, 47.2% met only clinical criteria, and 36.6% were confirmed in a laboratory. The overall case fatality rate was 2.1%, reaching 4.7% among infants aged 0–2 months. Of the confirmed cases, 23.1% occurred in subjects who received at

These epidemic situations detected in different countries have moved the scientific community and health professionals to seek an understanding of this alarming new situation to identify the causes [34–36], and review and implement new strategies for the control of pertussis [37]. Though several factors apparently contribute to this pertussis-case increase, a consensus exists in identifying, as part of the causes of the epidemic, several factors related to the vaccines currently in use and the vaccination—for example, suboptimal coverage of the three primary doses, noncompliance with vaccination schedule timing (delayed vaccination) [22, 38], the waning of vaccination-conferred immunity [39–41], and the circulation of a resistant bacterial population resulting from the selection pressure exerted by mass vaccination [36]. Probably,

To assess the trends of the disease in real time, a reliable and specific pertussis diagnosis is required. Laboratory diagnosis is also important to distinguish between the several etiologic agents of pertussis-like diseases, which involve both viruses and bacteria (i.e., adenovirus, parainfluenza viruses, respiratory syncytial virus, *Mycoplasma pneumoniae*, and *Chlamydophila pneumonia*) [42].

The clinical case definition used is based on CDC/WHO clinical criteria (www.cdc.gov/ncphi/ disss/nndss/casedef/pertussis\_current.htm, www.who.int/entity/immunization\_monitoring/

in 2016, the recommendation was extended for all pregnancies.

the relative contributions of each factor may differ between countries.

least three doses of the pertussis vaccine [33].

14 Pertussis - Disease, Control and Challenges

**3. Clinical case definition**

Although classical pertussis can be diagnosed reliably based on clinical symptoms, infections in infants, older vaccinated children, adolescents, and adults often follow an atypical course. In these cases, the diagnosis of pertussis requires laboratory methods for confirmation. The laboratory criteria for diagnosis are mainly based on isolation of *B. pertussis* from clinical specimen and/or through PCR for *B. pertussis* or serology.
