Pertussis is an acute bacterial, highly contagious respiratory infection with a significant morbidity and mortality, especially in infants.¹ In the United States, prior to the advent of vaccines, pertussis was the number one cause of communicable disease death in children <14 years old, accounting for 10,000 deaths annually. It was responsible for more deaths in the first year of life than measles, meningitis, scarlet fever, diphtheria, and poliomyelitis combined.^2,3 With the widespread use of the pertussis vaccine, there was a >90% drop in the number of cases, reaching a nadir in 1976, with an increase in the incidence since then. Epidemic pertussis has occurred every 2 to 5 years since 1989.^1–3

Worldwide, it was estimated by the World Health Organization (WHO) that in 2008 there were about 16 million cases of pertussis with 195,000 deaths.⁴ The incidence is highin developing countries and nations with low vaccination rates. In the developing world, disease rates are greatest in young children, while in the developed world, disease rates are highest in infants who are too young to be fully vaccinated.^5–7 Although pertussis can occur all year long, it is most frequent in the late summer and fall.^1,8

In the United States and Europe, in spite of widespread vaccination, the incidence has been increasing.^1–3 For adolescents and adults, the approximate number of cases per year in the United States is 600,000.² Moreover, it is underreported, particularly in adults and adolescents, with reported cases only 15% to 25% of the actual number.¹

In the United States, epidemics occur every 2 to 5 years.⁷ Recent epidemics occurred in 2005, 2010, 2012, and 2014, with 2012 being the largest outbreak in 60 years, when >48,000 cases were reported.⁵

The resurgence of this vaccine-preventable disease has been attributed to several factors: (1) increased awareness of the disease, (2) availability of better laboratory tests for detection of Bordetella pertussis, (3) genetically modified changes in B. pertussis, (4) waning immunity—either infection, acquired (after 4–20 years) or vaccination (after 4–12 years),⁹ (5) vaccine failures secondary to decreased potency of the vaccines or not effective against all strains of Bordetella, and (6) individuals unimmunized for religious or other reasons.

The clinical definition for pertussis is in the absence of a more likely diagnosis, an acute cough ≥14 days, plus one or more of the following: paroxysms of coughing, inspiratory whoop, post-tussive emesis, and in infants <1 year of age, apnea.² Pertussis, or “whooping cough,” is characterized by severe episodes of coughing followed by a forceful inspiration against a partially closed glottis, which causes the classic whooping sound.

Pertussis has a 3- to 12-day incubation period, lasts 6 to 10 weeks, and is characterized by three stages: catarrhal, paroxysmal, and convalescent (Table 38-1). The catarrhal phase, which lasts 1 to 2 weeks, consists of nonspecific upper respiratory infection (URI) symptoms. Fever is rarely present and if present is low grade, and suggests a secondary bacterial infection (Table 38-1).

The next stage is the paroxysmal phase, characterized by paroxysms of coughing with increased frequency at night and lasting from 2 to 6 weeks. There are consecutive (usually 10–15) rapid-fire coughs, the patient looks anxious, their face turns red or purple, their eyes bulge, their tongue protrudes, and they may have an inspiratory whoop and post-tussive emesis.

During the convalescent phase, the coughing episodes decrease in severity, except in infants.

Many infants have an atypical presentation that lacks the classic signs and symptoms. The classic presentation occurs most frequently as a primary infection in unimmunized children, whereas atypical presentations are the rule in infants and adults.

Young infants, especially those ≤3 months of age, usually do not have the classic three-stage presentation. The catarrhal phase may be unrecognized or shortened to a few days. The cough (expiratory grunt) and the whoop (forceful inspiratory gasp) may not be prominent findings.

Infants may have choking, gasping, and apnea, which may be triggered by minimal stimulation, such as from a sound or light, from sucking, stretching, or even suctioning. Apnea may be the only manifestation of the disease. In infants, the coughing may worsen during the convalescent phase instead of gradually getting better. Infants may have a prolonged convalescent stage with episodic paroxysmal spells triggered by other illnesses. Another presentation of pertussis in infants younger than 6 months is “silent” paroxysms. The infant appears to be coughing or not breathing with no audible sounds and may become unresponsive or hypoxic and even suffer complications from hypoxic encephalopathy.

Adolescents and adults can be asymptomatic, or have mild symptomatic disease, or even classic pertussis. They most commonly present with prolonged cough and do not have the characteristic whoop or the three distinct stages. Age, previous immunization or infection, antibiotic treatment, and the presence of passively acquired antibodies affect the clinical presentation.

At least 30% of adolescents and adults with pertussis present with a nonspecific cough illness with a prolonged cough, generally ≥21 days.² One-fourth of college students with a cough for 6 or more days had culture-proven B. pertussis, and none were diagnosed clinically.¹⁰ Similar results have been noted in adults, with a 20% incidence of B. pertussis by laboratory testing.^11,12 Pertussis has been reported in up to 32% of adolescents and adults with a cough of greater than 7 days.²

The lack of findings on physical examination, the absence of a fever, and lack of sputum tends to make health care practitioners overlook the diagnosis of pertussis. Occasionally, adults and adolescents with pertussis will present with syncope from the severe coughing spells. A lack of systemic signs and symptoms is a hallmark of pertussis.

Physical examination in patients with pertussis is usually unremarkable, with a normal lung examination unless a complicating pneumonia is present. However, severe coughing may lead to conjunctival hemorrhages and petechiae, a torn frenulum in infants, subcutaneous emphysema, and rib fractures.^1,8

The clinical presentation may be atypical, even in children. The presentation can be just like a viral respiratory infection, and a paroxysmal cough is not always a reliable indicator of pertussis. Recent studies indicate that clinical assessment alone would miss about one out of five cases.¹³ The spectrum of clinical pertussis ranges from asymptomatic to mild (such as a URI without a severe paroxysmal cough or whoop) to severe life-threatening disease.¹

Consider pertussis in any individual with the chief complaint of cough, particularly if they lack the following signs or symptoms: myalgia, malaise, exanthem, enanthem, fever, tachypnea, and have a normal lung examination without wheezing, rales, or rhonchi, and a normal chest roentgenogram.

Pertussis should be considered in infants with any of the following: gasping, gagging, cyanosis, apnea, or a brief resolved unexplained event (BRUE) which has replaced apparent life threatening event (ALTE) (see Chapter 4), and it has been linked to sudden infant death.^1,8 It should be in the differential diagnosis of an older child with a cough that is worsening at 7 to 10 days and any individual of any age with a prolonged cough.² About half of the adolescents with pertussis will cough for 10 weeks or longer. Pertussis means “violent cough” (Latin), and has been dubbed the cough of 100 days.

Several other respiratory pathogens can cause a prolonged, repetitive cough, including other Bordetella species (e.g., B. parapertussis, B. holmesii), Mycoplasma pneumoniae, Chlamydophila pneumoniae, influenza, parainfluenza, enteroviruses, respiratory syncytial virus (RSV), adenovirus, bocavirus, and others.^1,2,8 Coughing episodes may be associated with respiratory diseases such as asthma and cystic fibrosis, to pulmonary infections including pneumonia, bronchiolitis, tuberculosis, coccidioides, and histoplasmosis. Cough may also be a consequence of airway foreign body, sinusitis, and gastroesophageal reflux.

Concurrent infection with RSV or adenovirus has been noted frequently. One study noted that one-third of hospitalized infants with culture positive pertussis also had a concurrent RSV infection.¹⁴

The most recent CDC clinical case definition and case classifications of pertussis are listed in Tables 38-2 and 38-3.¹⁵ However, there are other case definitions for pertussis including one by the World Health Organization (WHO) and a consensus-based definition based on whether or not there is access to laboratory facilities or clinical capabilities only, with further delineation by the patient’s age and duration of cough.¹⁶

B. pertussis belongs to the Bordetella genus of bacteria, which consists of small, gram-negative, pleomorphic, aerobic coccobacilli. It affects only humans and has no known animal or environmental reservoir.³ B. parapertussis causes 5% to 14% of pertussis cases, is clinically similar to B. pertussis infection, but is usually less severe.¹ B. holmesii has been associated with respiratory infections in humans and other mammals, and can cause non-pulmonary infections including bacteremia, which is not the case for B. pertussis.³ B. bronchiseptica has been reported to cause a severe respiratory illness in immunocompromised patients and is the organism responsible for kennel cough in animals.^3,17