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Pertussis, literally meaning “a violent cough,” and also known as whooping cough, or “the cough of 100 days,” was first described in the Paris epidemic of 1578. Bordetella pertussis, the causative organism, was discovered in 1906, and a vaccine was developed in the 1940s. Before the pertussis vaccine was developed, pertussis was a major cause of infant morbidity and mortality.[rx][rx][rx]
Pertussis is a serious illness with very high morbidity and mortality.
Causes of Pertussis
The causative organisms of pertussis are Bordetella pertussis and Bordetella parapertussis. Bordetella is spread by airborne droplets and is
highly contagious. Pertussis often affects 100% of non-immune household contacts. Immunity wanes to 50% 12 years after completing a vaccination series. Immunocompromised persons can also contract Bordetella bronchiseptica, which typically affects animals and is commonly known as “a kennel cough.”[rx][rx][rx]
Humans are the sole reservoir for Bordetella; the organism is spread via aerosolized droplets produced during a cough. The organism is highly contagious with majority of cases occuring during summer.
Risk factors for acquiring pertussis include:
- Epidemic exposure
- Lack of immunization
- Close contact with an infected individual
Bordetella is a gram-negative coccobacillus that adheres to ciliated respiratory epithelial cells. Local inflammatory changes occur in the mucosal lining of the respiratory tract. Released toxins (pertussis toxin, dermonecrotic toxin, adenylate cyclase toxin, and tracheal cytotoxin) act locally and systemically, although the organism itself does not fully penetrate the respiratory tract, and almost never is found in blood cultures.
Diagnosis of Pertussis
History and Physical
After an incubation period of 1 to 3 weeks, pertussis infection typically progresses through three distinct stages: the catarrhal phase, the paroxysmal phase, and the convalescent phase.
The catarrhal phase presents similarly to other upper respiratory tract infections, with fever, fatigue, rhinorrhea, and conjunctival injection. The catarrhal phase lasts 1 to 2 weeks and is the most infectious stage of the disease.
The paroxysmal phase follows the catarrhal phase and is characterized by paroxysms of a staccato cough and resolution of fever. The patient typically coughs repeatedly, followed by forceful inspiration which creates the characteristic “whoop.” These episodes may be triggered by cold or noise, and are more common at night. Patients are nontoxic-appearing in between outbreaks, but during coughing episodes may exhibit cyanosis, diaphoresis, or apnea. Immediately following a paroxysm, patients may develop post-tussive vomiting, syncope, or apnea.
Finally, during the convalescent phase, a residual cough persists for weeks to months, usually triggered by exposure to another upper respiratory infection or irritant.
Atypical presentations are common in infants, and fever may not occur. Rather, tachypnea, apnea, cyanosis, and episodic bradycardia may be the presenting features.
Increased intrathoracic pressure from coughing may result in petechiae above the nipple line, subconjunctival hemorrhage, and epistaxis.
Breath sounds are variable; auscultation may reveal clear lungs or rhonchi, while rales suggest superimposed pneumonia. The inspiratory whoop or gasp is usually heard in children in between 6 months to 5 years.
Testing for pertussis is not readily available in the emergency department. Nasopharyngeal culture and PCR may make laboratory confirmation, but the fastidious and slow-growing Bordetella organisms require specialized media and cultures are typically not positive for 3 to 7 days. In adults, by the time the diagnosis is suspected, cultures are typically negative (96%), and overall culture sensitivity is only 20% to 40%. PCR is more sensitive and specific than culture, but testing is not widely available.[rx][rx][rx]
In the emergency department, pertussis should be considered in patients with prolonged cough, especially occurring in paroxysms or with whoops, or post-tussive emesis. During the late catarrhal and early paroxysmal phases, leukocytosis (often 25,000 to 60,000 per mL) with lymphocytosis may raise suspicion for pertussis. In a study of 100 infants, less than 120 days old, and admitted to a pediatric intensive care unit, there was a significantly higher leukocytosis in the five fatal cases. Unfortunately, leukocytosis may be the only laboratory finding useful in the emergency department. Chest x-ray findings are nonspecific and may show peribronchial thickening, atelectasis, or infiltrate. The classic association, though not often seen, is a “shaggy” right heart border.
Treatment of pertussis is largely supportive, including oxygen, suctioning, hydration, and avoidance of respiratory irritants. Parenteral nutrition may be necessary as the disease tends to have a prolonged course.
Hospitalization is indicated for patients with superimposed pneumonia, hypoxia, central nervous system (CNS) complications, or who are unable to tolerate nutrition and hydration by mouth. Patients less than 1-year-old are not fully vaccinated and carry the greatest risk of morbidity and mortality; they should be hospitalized regardless of symptoms. Neonates should be admitted to an intensive care setting as life-threatening cardiopulmonary complications and arrest can occur unexpectedly.
Antibiotic effect on the duration or severity of the disease is minimal when started in the catarrhal phase, and not proven effective when started in the paroxysmal phase. Rather, the primary goal of antibiotic treatment is to decrease carriage and spread of disease. Erythromycin (40 to 50 mg/kg per day, maximum 2 g per day, in 2 to 3 divided doses) is the first-line treatment for pertussis. Azithromycin (10 mg/kg per day on day 1 followed by 5 mg/kg on days 2 to 5) and clarithromycin (15 mg/kg per day in two divided doses) are alternative treatments. Trimethoprim-sulfamethoxazole (8 mg/kg per day of trimethoprim) has been used as an alternative in macrolide-allergic patients, but its efficacy has not been proven.
The macrolides are not recommended for infants less than 4 weeks old for fear that this may lead to infantile hypertrophic pyloric stenosis.
Strict isolation is important while the patient remains infectious. Pertussis is contagious throughout the catarrhal phase and for 3 weeks after the onset of the paroxysmal phase. In patients treated with antibiotics, isolation should be continued for at least 5 days after treatment is initiated. Postexposure prophylaxis with erythromycin is recommended for all household contacts.
Corticosteroids have not shown definite benefit in reducing severity and course of illness, but are sometimes given to critically-ill infants. Beta2-agonists, pertussis immune globulin, cough suppressants, and antihistamines are not effective. Exchange blood transfusion therapy for leukocytosis with lymphocytosis may be considered.
Close contacts should be treated with azithromycin or erythromycin.
Vaccination is recommended with the acellular vaccine at ages 2,4,6, 15-18 months and at age 4-6 years. In addition, the CDC recommends a single dose of Tdap for all adults to reduce transmission to children. Adverse effects of the vaccine include crying and febrile seizures but severe neurological effects are rare. The vaccine can also be administered during the third trimester to pregnant women without causing harm to the fetus.
Pertussis initially presents similarly to other respiratory infections, such as viral upper respiratory infection, bronchiolitis, pneumonia, and tuberculosis. Key differentiating factors of pertussis include typical progression through the three phases and persistent cough without fever. Foreign body aspiration should be considered in younger patients, and exacerbation of chronic obstructive pulmonary disease should be considered in older patients with the appropriate history. The striking leukocytosis may also be confused for leukemia.
Secondary pneumonia or otitis media may occur. Superimposed pneumonia is a major cause of mortality in infants and young children, and maybe caused by aspiration of gastric contents during paroxysms of cough or because of decreased respiratory clearance of pathogens. Fever should subside during the catarrhal phase, and its presence during the paroxysmal phase should raise suspicion for pneumonia. The most common causes of secondary bacterial pneumonia are Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and Staphylococcus aureus; although viral infections with the respiratory syncytial virus, cytomegalovirus, and adenovirus superinfections are also common.
Rarely (less than 2% of cases), CNS complications such as seizures and encephalopathy can occur, likely secondary to hypoxia, hypoglycemia, toxins, secondary infections, or cerebral bleeding from increased pressure during coughing. Sudden increases in intrathoracic and intraabdominal pressures can also result in periorbital edema, pneumothorax, pneumomediastinum, subcutaneous emphysema, diaphragmatic rupture, umbilical and inguinal hernias, and rectal prolapse.
Pertussis toxin also causes histamine hypersensitivity and increased insulin secretion.
Infants are particularly prone to bradycardia, hypotension, and cardiac arrest from pertussis. Development of pulmonary hypertension has been increasingly recognized as a factor contributing to infantile mortality, as it may lead to worsening systemic hypotension and hypoxia.