Pertussis or whooping cough is an infectious disease caused by Bordetella pertussis , a gram- negative bacillus.

Before the introduction of the whole-cell vaccine , there were over 250,000 cases of whooping cough per year and 10,000 deaths worldwide. The incidence of pertussis declined significantly with the implementation of universal vaccination. Pertussis incidence has been gradually increasing since the early 1980s. A total of 28,000 cases were reported in 2014, the largest number since 1959. The reasons for the increase are not clear. A total of 27,550 pertussis cases and 27 pertussis-related deaths were reported in 2010. The increase in disease incidence in the USA has mostly been seen in older children and adults, likely reflecting waning immunity conferred by the vaccine, decreasing natural immunity, as well as decreasing vaccination rates. The numbers may underestimate the reality as this disease is underdiagnosed in adults [ 1 ].

Bordetella pertussis is a small, fastidious aerobic gram-negative rod, requiring specialized medium for culture. It produces multiple antigenic and biologically active products including pertussis toxin, filamentous hemagglutinin , agglutinogens, adenylate cyclase, pertactin, and tracheal cytotoxin. These products are responsible for the clinical features of pertussis disease, and an immune response to one or more produces immunity following infection.

The clinical presentation varies slightly between children and adults. In general, whooping cough is divided into three phases: the catarrhal or prodromal stage, the paroxysmal stage, and the convalescent stage. During the catarrhal stage, children present with signs and symptoms of an upper respiratory tract infection such as rhinorrhea, conjunctivitis, occasional cough, and fever. This generally lasts from 1 to 2 weeks. The paroxysmal stage is characterized by repeated episodes of severe cough accompanied by fits of spasm and, at the end of the paroxysm, may be accompanied by the classic whooping sound produced when rapidly inspiring air against a closed glottis. With the force of the coughing, children will often cough mucous plugs and can be accompanied by post-tussive emesis. These attacks occur more frequently at night. The paroxysmal stage can last as long as 6 weeks. Lastly, symptoms begin to wane and patients move on to the convalescent phase. Pertussis in adults can have a more atypical presentation, often appearing as a chronic cough [ 2 ] with a less defined course than classically described in children.

Whole-cell pertussis vaccine is composed of a formalin- inactivated suspension of B. pertussis cells. It was developed in the 1930s and has been available in practice since the 1940s. Based on efficacy studies, the vaccine conferred 70–90 % efficacy in protecting from severe pertussis. Local reactions were common and occasionally would be accompanied by fever. This led to the creation of an acellular vaccine associated with less adverse effects. Whole-cell pertussis vaccine is no longer available in the USA but is still available elsewhere. Acellular vaccines are subunit vaccines that contain inactivated components of Bordetella pertussis . These are only available in combination with diphtheria and tetanus toxoid. Efficacy has ranged from 80 to 85 % [ 3 ]. The primary series of DTaP vaccines consists of four doses, the first three doses given at 4- to 8-week intervals (minimum of 4 weeks), and beginning at 6 weeks to 2 months of age. The fourth dose is given 6–12 months after the third to maintain adequate immunity for the ensuing preschool years [ 3 ].

References
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[1] Atkinson W, Wolfe S, Hamborsky J (2012) Centers for Disease Control and Prevention. Epidemiology and prevention of vaccine, 12th edn, 2nd printing. Washington, DC: Public Health Foundation

 [2] Senzilet LD, Halperin SA, Spika JS et al (2001) Pertussis is a frequent cause of pro longed cough illness in adults and adolescents. Clin Infect Dis 32:1691–1697

[3] CDC (2011) Updated recommendations for use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) Vaccine from the Advisory Committee on Immunization Practices (ACIP). MMWR 60(1):13–15