Pertussis is a highly communicable disease occurring mostly in children and adolescents and caused by the gram-negative bacterium Bordetella pertussis. Symptoms are initially those of nonspecific upper respiratory infection followed by paroxysmal or spasmodic coughing that usually ends in a prolonged, high-pitched, crowing inspiration (the whoop). Diagnosis is by nasopharyngeal culture, polymerase chain reaction testing, and serologic assays. Treatment is with macrolide antibiotics. Prevention includes immunization and, when needed, postexposure prophylaxis.
Infection with B. pertussis occurs only in humans; there are no animal reservoirs. B. bronchiseptica, which causes kennel cough in dogs and cats, can cause infection in patients who are immunocompromised (1).
Transmission is mainly via droplets of respiratory secretions that contain B. pertussis (a small, nonmotile, gram-negative coccobacillus) from infected patients, particularly during the catarrhal and early paroxysmal stages. The infection is highly contagious and causes disease in ≥ 80% of close contacts. Transmission by contact with contaminated articles is rare. Patients are usually not infectious after the third week of the paroxysmal phase.
Pertussis is a vaccine-preventable childhood disease that is endemic throughout the world and has been increasing in incidence. Its incidence in the United States cycles, with peaks in incidence every 3 to 5 years. In the United States, the case rate in the 1980s was at an all-time low of about 1/100,000 population, which, by 2014, increased to about 10/100,000. The 2022 surveillance report by the Centers for Disease Control and Prevention (CDC) reported an incidence of 0.7/100,000 (2). The observed increase from the 1980s until 2014 can be attributed to
Waning immunity in previously vaccinated adolescents and adults
Some parents refusing to vaccinate their children (see Vaccine Hesitancy)
Such unprotected patients may become ill; furthermore, unprotected adolescents and adults are an important reservoir for B. pertussis and are thus often the source of infection for unprotected infants < 1 year (who have had the highest increase in annual incidence and the highest case fatality rate). Pertussis is also serious in older adults. Virulence of outbreak strains may be increasing.
In the United States in 2022, there were 2,388 reported pertussis cases and 3 deaths. One factor contributing to the decrease in incidence from 2014 to 2022 is thought to be increased immunization, particularly for adults and pregnant people. The incidence per 100,000 was highest in infants < 6 months old (7.8) (2). People > 20 years old accounted for 45.6% of the reported cases (2).
One attack does not confer lifelong natural immunity, but secondary attacks and infections in previously vaccinated adolescents and adults whose immunity has waned are usually mild and often unrecognized.
Complications caused by pertussis
Respiratory complications, including asphyxia in infants, are most common. Otitis media occurs frequently. Bronchopneumonia (common among older adults) may be fatal at any age.
Seizures are common among infants but are 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, or other neurologic disorders.
Umbilical hernia and rectal prolapse occasionally occur.
Parapertussis
This disease, caused by B. parapertussis, may be clinically indistinguishable from pertussis but is usually milder and less often fatal.
General references
1. Yacoub AT, Katayama M, Tran J, Zadikany R, Kandula M, Greene J. Bordetella bronchiseptica in the immunosuppressed population - a case series and review. Mediterr J Hematol Infect Dis. 2014;6(1):e2014031. Published 2014 Apr 7. doi:10.4084/MJHID.2014.031
2. National Center for Immunization and Respiratory Diseases Division of Bacterial Diseases: 2022 Provisional Pertussis Surveillance Report. Centers for Disease Control and Prevention, 2023.
Symptoms and Signs of Pertussis
The incubation period averages 7 to 10 days (maximum 3 weeks). 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 weeks and consists of 3 stages:
Catarrhal
Paroxysmal
Convalescent
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 weeks of onset. Average duration of illness is about 7 weeks (range 3 weeks to 3 months or more). Paroxysmal coughing may recur for months, usually induced in the still sensitive respiratory tract by irritation from an upper respiratory infection.
Diagnosis of Pertussis
Nasopharyngeal cultures, direct fluorescent antibody testing, and polymerase chain reaction (PCR) testing
Serologic testing
Pertussis should be suspected in patients with cough that lasts ≥ 2 weeks and who have at least 1 of the following (1):
Inspiratory whoop
Coughing paroxysms
Post-tussive emesis
Occurrence during a known or suspected outbreak (2)
Diagnostic testing is done whenever a clinician suspects pertussis.
The catarrhal stage is often difficult to distinguish from bronchitis or influenza. Adenovirus infections and tuberculosis 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. Paired acute and convalescent serologic testing may be helpful, particularly after the catarrhal stage.
PCR testing of nasopharyngeal samples is the preferred test; when done within about the first 4 weeks (catarrhal and paroxysmal stages), it has the highest sensitivity (90 to 100%) and specificity of up to 100% (3).
The white blood cell count is usually between 15,000 and 20,000/mcL (15 and 20 × 109/L) but may be normal or as high as 60,000/mcL (60 × 109/L), usually with 60 to 80% small lymphocytes. Marked lymphocytosis in infants < 6 months of age portends a poor prognosis (4).
Parapertussis is differentiated by culture or the fluorescent antibody technique.
Diagnosis references
1. Centers for Disease Control and Prevention. Pertussis (Whooping Cough). Surveillance & Reporting. Accessed January 24, 2024.
2. Patriarca PA, Biellik RJ, Sanden G, et al. Sensitivity and specificity of clinical case definitions for pertussis. Am J Public Health. 1988;78(7):833-836. doi:10.2105/ajph.78.7.833
3. Lee AD, Cassiday PK, Pawloski LC, et al. Clinical evaluation and validation of laboratory methods for the diagnosis of Bordetella pertussis infection: Culture, polymerase chain reaction (PCR) and anti-pertussis toxin IgG serology (IgG-PT). PLoS One. 2018;13(4):e0195979. Published 2018 Apr 13. doi:10.1371/journal.pone.0195979
4. Coquaz-Garoudet M, Ploin D, Pouyau R, et al. Malignant pertussis in infants: factors associated with mortality in a multicenter cohort study. Ann Intensive Care. 2021;11(1):70. Published 2021 May 7. doi:10.1186/s13613-021-00856-y
Treatment of Pertussis
Supportive care
Erythromycin or azithromycin
Hospitalization with respiratory droplet 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. Oxygen 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 isolated, particularly from susceptible infants, for at least 4 weeks from disease onset and until symptoms have subsided.
Antibiotics given during the catarrhal stage have been found to help ameliorate the disease. After paroxysms are established, antibiotics have been found to have a limited clinical effect but are recommended to limit spread.
Preferred antibiotics are
Erythromycin for 14 days
Azithromycin for 5 days
Azithromycin is preferred in infants ≤ 6 weeks old because erythromycin has a higher risk of infantile hypertrophic pyloric stenosis (1).
Trimethoprim/sulfamethoxazole may be substituted in patients ≥ 2 months old who are intolerant of or hypersensitive to macrolide antibiotics.
Antibiotics should also be used for bacterial complications (eg, bronchopneumonia, otitis media).
Treatment reference
1. Maheshwai N. Are young infants treated with erythromycin at risk for developing hypertrophic pyloric stenosis?. Arch Dis Child. 2007;92(3):271-273. doi:10.1136/adc.2006.110007
Prevention of Pertussis
Immunization
Active immunization against pertussis is recommended for all infants, children, adolescents, and adults, including pregnant women.
For children under 7 years of age, see Diphtheria-Pertussis-Tetanus Vaccine for more information, including indications, contraindications and precautions, dose and administration, and adverse effects.
For people over 7 years of age, see Tetanus-Diphtheria Vaccine for more information, including indications, contraindications and precautions, dose and administration, and adverse effects.
Immunity after natural infection lasts about 20 years.
Close contacts < 7 years old who have had < 4 doses of vaccine should complete the recommended childhood vaccination schedule.
Postexposure prophylaxis
Postexposure antibiotics should be given to household contacts within 21 days of the onset of cough in the index patient, whether they have been vaccinated or not.
Postexposure antibiotics should also be given to the following people at high-risk of severe disease within 21 days of exposure, whether they have been vaccinated or not:
Infants < 12 months
Women in the third trimester of pregnancy
All people with health conditions potentially exacerbated by pertussis infection (eg, immunodeficiency, moderate to severe asthma, chronic lung disease)
People who have close contact with infants < 12 months, pregnant women, or patients with conditions that may result in severe illness or complications
All people in high-risk settings that include infants < 12 months or women in the third trimester of pregnancy (eg, child care centers, maternity wards, neonatal intensive care units)
These people should be given a standard 5-day course of azithromycin. A 7- to 14-day course of erythromycin or clarithromycin (7 days) is an alternative. For infants < 1 month, azithromycin is preferred for postexposure prophylaxis.
Key Points
Pertussis is a respiratory infection that can occur at any age but is most common and most likely to be fatal in young children, particularly infants < 6 months old.
A catarrhal stage with upper respiratory infection symptoms is followed by a paroxysmal stage with repeated bouts of rapid, consecutive coughs followed by a hurried, deep inspiration (the whoop).
The illness lasts about 7 weeks, but cough may continue for months.
Diagnose using polymerase chain reaction testing or nasopharyngeal cultures; special media are required.
Treat with a macrolide antibiotic to ameliorate disease (during the catarrhal stage) or to minimize transmission (during the paroxysmal stage and later).
Prevent the disease by giving an acellular pertussis vaccine as part of scheduled immunization and give booster doses at varying intervals; treat close contacts with a macrolide.
Neither having the disease nor being vaccinated provides lifelong protection, although any subsequent disease tends to be milder.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
MSD Veterinary Manual: Kennel Cough
Centers for Disease Control and Prevention (CDC): Pertussis (Whooping Cough): Clinicians
