Cough in Children: A Merck Manual of Patient Symptoms podcast
Pertussis is a highly communicable disease occurring mostly in children and adolescents and caused by Bordetella pertussis. Symptoms are initially those of nonspecific URI followed by paroxysmal or spasmodic coughing that usually ends in a prolonged, high-pitched, crowing inspiration (the whoop). Diagnosis is by nasopharyngeal culture, PCR, and serologic assays. Treatment is with macrolide antibiotics.
Pertussis is endemic throughout the world. Its incidence in the US cycles every 3 to 4 yr. In a given unimmunized locality, it becomes epidemic every 2 to 4 yr. It occurs at all ages, but 71% of cases occur in children < 5 yr, and 38% of cases, including nearly all deaths, occur in infants < 6 mo. Mortality is about 1 to 2% in children < 1 yr and is highest during the first month of life. Most deaths are caused by bronchopneumonia and cerebral complications. It is also serious in the elderly. One attack does not confer life-long natural immunity, but secondary attacks are usually mild and often unrecognized.
Transmission via aerosols of B. pertussis (a small, nonmotile, gram-negative coccobacillus) from infected patients, particularly in the catarrhal and early paroxysmal stages, causes disease in 90 to 100% of close contacts. Transmission by contact with contaminated articles is rare. Patients are usually not infectious after the 3rd wk of the paroxysmal phase.
Diseases caused by pertussis
Respiratory complications, including asphyxia in infants, are most common. Otitis media occurs frequently. Bronchopneumonia (common among the elderly) may be fatal at any age. Seizures are common among infants but rare in older children. Hemorrhage into the brain, eyes, skin, and mucous membranes can result from severe paroxysms and consequent anoxia. Cerebral hemorrhage, cerebral edema, and toxic encephalitis may result in spastic paralysis, intellectual disability (mental retardation), or other neurologic disorders. Umbilical herniation and rectal prolapse occasionally occur.
This disease, caused by B. parapertussis, may be clinically indistinguishable from pertussis but is usually milder and less often fatal.
Symptoms and Signs
The incubation period averages 7 to 14 days (maximum 3 wk). B. pertussis invades respiratory mucosa, increasing the secretion of mucus, which is initially thin and later viscid and tenacious. Uncomplicated disease lasts about 6 to 10 wk and consists of 3 stages:
The catarrhal stage begins insidiously, generally with sneezing, lacrimation, or other signs of coryza; anorexia; listlessness; and a troublesome, hacking nocturnal cough that gradually becomes diurnal. Hoarseness may occur. Fever is rare.
After 10 to 14 days, the paroxysmal stage begins with an increase in the severity and frequency of the cough. Repeated bouts of ≥ 5 rapidly consecutive forceful coughs occur during a single expiration and are followed by the whoop—a hurried, deep inspiration. Copious viscid mucus may be expelled or bubble from the nares during or after the paroxysms. Vomiting is characteristic. In infants, choking spells (with or without cyanosis) may be more common than whoops.
Symptoms diminish as the convalescent stage begins, usually within 4 wk of onset. Average duration of illness is about 7 wk (range 3 wk to 3 mo). Paroxysmal coughing may recur for months, usually induced in the still sensitive respiratory tract by irritation from a URI.
The catarrhal stage is often difficult to distinguish from bronchitis or influenza. Adenovirus infections and TB should also be considered.
Cultures of nasopharyngeal specimens are positive for B. pertussis in 80 to 90% of cases in the catarrhal and early paroxysmal stages. Because special media and prolonged incubation are required, the laboratory should be notified that pertussis is suspected. Specific fluorescent antibody testing of nasopharyngeal smears accurately diagnoses pertussis but is not as sensitive as culture. PCR can also be used. The WBC count is usually between 15,000 and 20,000/μL but may be normal or as high as 60,000/μL, usually with 60 to 80% small lymphocytes.
Parapertussis is differentiated by culture or the fluorescent antibody technique.
Hospitalization with respiratory isolation is recommended for seriously ill infants. Isolation is continued until antibiotics have been given for 5 days.
In infants, suction to remove excess mucus from the throat may be lifesaving. O2 and tracheostomy or nasotracheal intubation is occasionally needed. Expectorants, cough suppressants, and mild sedation are of little value. Because any disturbance can precipitate serious paroxysmal coughing with anoxia, seriously ill infants should be kept in a darkened, quiet room and disturbed as little as possible. Patients treated at home should be quarantined, particularly from susceptible infants, for at least 4 wk from disease onset and until symptoms have subsided.
Antibiotics given during the catarrhal stage may ameliorate the disease. After paroxysms are established, antibiotics usually have no clinical effect but are recommended to limit spread. Preferred drugs are erythromycin 10 to 12.5 mg/kg po q 6 h (maximum 2 g/day) for 14 days or azithromycin 10 to 12 mg/kg po once/day for 5 days. Antibiotics should also be used for bacterial complications (eg, bronchopneumonia, otitis media).
Active immunization is part of standard childhood vaccination. Five doses of vaccine are given (usually combined with diphtheria and tetanus [DTP or DTaP]) at age 2, 4, and 6 mo; boosters are given at 15 to 18 mo and 4 to 6 yr. Significant adverse effects from the pertussis component of the vaccine include encephalopathy within 7 days; seizure, with or without fever, within 3 days; persistent, severe, inconsolable screaming or crying for ≥ 3 h; collapse or shock within 48 h; fever ≥ 40.5° C within 48 h; and immediate severe or anaphylactic reaction. These reactions contraindicate further use of pertussis vaccine; combined diphtheria and tetanus vaccine is available without the pertussis component. The acellular vaccine (DTaP) is better tolerated.
Immunity after natural infection lasts about 20 yr. Passive immunization is unreliable and is not recommended.
Close contacts < 7 yr who have had < 4 doses of vaccine should be vaccinated. Contacts of all ages, whether vaccinated or not, should receive a 10-day course of erythromycin 500 mg po qid or 10 to 12.5 mg/kg po qid.
Last full review/revision August 2009 by Burke A. Cunha, MD