Pertussis (Bordetella pertussis and Bordetella parapertussis)

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Chapter 189 Pertussis (Bordetella pertussis and Bordetella parapertussis)

Pertussis is an acute respiratory tract infection that was well described initially in the 1500s. Sydenham first used the term pertussis, meaning intense cough, in 1670; it is preferable to whooping cough because most infected individuals do not “whoop.”

Epidemiology

There are 60 million cases of pertussis each year worldwide, resulting in >500,000 deaths. Before vaccination was available, pertussis was the leading cause of death due to communicable disease among children <14 yr of age in the USA, with 10,000 deaths annually. Widespread use of pertussis vaccine led to a >99% decline in cases. The pivotal role of vaccination in disease control is reflected in the continued high incidence of pertussis in developing countries and the resurgence in other countries where vaccine coverage is low or where less potent vaccine may have been used.

After the low number of 1,010 cases in the USA reported in 1976, there was an increase in annual pertussis incidence to 1.2 cases/100,000 population from 1980 through 1989, with epidemic pertussis in many states in 1989-1990, 1993, and 1996. Since then pertussis has become increasingly endemic, with less cycling or seasonality and with shifting burden of disease to young infants, adolescents, and adults. By 2004, the incidence of reported pertussis in the USA was 8.9 cases/100,000 population, and the number of cases (25,827) was the highest reported since 1959. Of these cases, 10% occurred among infants <6 mo of age (incidence of 136.5/100,000 population). A total of 40 pertussis-related deaths were reported in 2005, and 16 in 2006; >90% occurred among young infants. Approximately 60% of cases currently are in adolescents and adults. Pertussis is the only vaccine-preventable disease for which universal immunization in the USA is recommended that continues to be endemic. Prospective and serologic studies suggest that pertussis is underrecognized, especially among adolescents and adults, in whom the actual number of cases is estimated to be 600,000 annually. A number of studies have documented pertussis in 13-32% of adolescents and adults with cough illness for >7 days.

Pertussis is extremely contagious, with attack rates as high as 100% in susceptible individuals exposed to aerosol droplets at close range. B. pertussis does not survive for prolonged periods in the environment. Chronic carriage by humans is not documented. After intense exposure as in households, the rate of subclinical infection is as high as 80% in fully immunized or previously infected individuals. When carefully sought, a symptomatic source case can be found for most patients.

Neither natural disease nor vaccination provides complete or lifelong immunity against pertussis re-infection or disease. Protection against typical disease begins to wane 3-5 yr after vaccination and is unmeasurable after 12 yr. Subclinical re-infection undoubtedly has contributed significantly to immunity against disease ascribed previously to both vaccine and prior infection. Despite history of disease or complete immunization, outbreaks of pertussis have occurred in the elderly, in nursing homes, in residential facilities with limited exposures, in highly immunized suburbia, and in preadolescents, adolescents, and adults with significant time since immunization. Possible explanations for change in epidemiology include waning immunity post immunization, an aging cohort who received less effective vaccine, and increased awareness and diagnosis. Without natural re-infection with B. pertussis or repeated booster vaccinations, adolescents and adults are susceptible to clinical disease if exposed, and mothers provide little if any passive protection to young infants. Coughing adolescents and adults (usually not recognized as having pertussis) are the major reservoir for B. pertussis and are the usual sources of infection for infants and children.

Clinical Manifestations

Classically, pertussis is a prolonged disease, divided into catarrhal, paroxysmal, and convalescent stages. The catarrhal stage (1-2 wk) begins insidiously after an incubation period ranging from 3-12 days with nondistinctive symptoms of congestion and rhinorrhea variably accompanied by low-grade fever, sneezing, lacrimation, and conjunctival suffusion. As initial symptoms wane, coughing marks the onset of the paroxysmal stage (2-6 wk). The cough begins as a dry, intermittent, irritative hack and evolves into the inexorable paroxysms that are the hallmark of pertussis. A well-appearing, playful toddler with insignificant provocation suddenly expresses an anxious aura and may clutch a parent or comforting adult before beginning a machine-gun burst of uninterrupted cough on a single exhalation, chin and chest held forward, tongue protruding maximally, eyes bulging and watering, face purple, until coughing ceases and a loud whoop follows as inspired air traverses the still partially closed airway. Post-tussive emesis is common, and exhaustion is universal. The number and severity of paroxysms escalate over days to a week and remain at that plateau for days to weeks. At the peak of the paroxysmal stage, patients may have more than 1 episode hourly. As the paroxysmal stage fades into the convalescent stage (≥2 wk), the number, severity, and duration of episodes diminish.

Infants <3 mo of age do not display the classic stages. The catarrhal phase lasts only a few days or is unnoticed, and then, after the most insignificant startle from a draft, light, sound, sucking, or stretching, a well-appearing young infant begins to choke, gasp, gag, and flail the extremities, with face reddened. Cough may not be prominent, especially in the early phase. Whoop infrequently occurs in infants <3 mo of age who at the end of a paroxysm lack stature or muscular strength to create sudden negative intrathoracic pressure. Apnea and cyanosis can follow a coughing paroxysm, or apnea can occur without a cough. Apnea may be the only symptom. Apnea and cyanosis both are more common with pertussis than with neonatal viral infections, including respiratory syncytial virus (RSV). The paroxysmal and convalescent stages in young infants are lengthy. Paradoxically, in infants, cough and whooping may become louder and more classic in convalescence. Convalescence includes intermittent paroxysmal coughing throughout the 1st yr of life, including “exacerbations” with subsequent respiratory illnesses; these are not due to recurrent infection or reactivation of B. pertussis.

Adolescents and previously immunized children have foreshortening of all stages of pertussis. Adults have no distinct stages. Classically, adolescents and adults describe a sudden feeling of strangulation followed by uninterrupted coughs, feeling of suffocation, bursting headache, diminished awareness, and then a gasping breath, usually without a whoop. Post-tussive emesis and intermittency of paroxysms separated by hours of well-being are specific clues to the diagnosis in adolescents and adults. At least 30% of older individuals with pertussis have nonspecific cough illness, distinguished only by duration, which is usually >21 days.

Findings on physical examination generally are uninformative. Signs of lower respiratory tract disease are not expected unless complicating secondary bacterial pneumonia is present. Conjunctival hemorrhages and petechiae on the upper body are common.

Diagnosis

Pertussis should be suspected in any individual who has pure or predominant complaint of cough, especially if the following features are absent: fever, malaise or myalgia, exanthem or enanthem, sore throat, hoarseness, tachypnea, wheezes, and rales. For sporadic cases, a clinical case definition of cough of ≥14 days’ duration with at least 1 associated symptom of paroxysms, whoop, or post-tussive vomiting has a sensitivity of 81% and a specificity of 58% for culture confirmation. Pertussis should be suspected in older children whose cough illness is escalating at 7-10 days and whose coughing episodes are not continuous. Pertussis should be suspected in infants <3 mo of age with gagging, gasping, apnea, cyanosis, or an apparent life-threatening event (ALTE). Sudden infant death is occasionally caused by B. pertussis.

Adenoviral infections are usually distinguishable by associated features, such as fever, sore throat, and conjunctivitis. Mycoplasma causes protracted episodic coughing, but patients usually have a history of fever, headache, and systemic symptoms at the onset of disease as well as more continuous cough and frequent finding of rales on auscultation of the chest. Epidemics of Mycoplasma and B. pertussis in young adults can be difficult to distinguish on clinical grounds. Although pertussis is often included in the laboratory evaluation of young infants with afebrile pneumonia, B. pertussis is not associated with staccato cough (breath with every cough), purulent conjunctivitis, tachypnea, rales or wheezes that typify infection due to Chlamydia trachomatis, or predominant lower respiratory tract signs that typify infection due to RSV. Unless an infant with pertussis has secondary pneumonia (and then appears ill), the findings on examination between paroxysms are entirely normal, including respiratory rate.

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