Pertussis natural history, complications and prognosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S. [2]; Rim Halaby, M.D. [3]

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Overview

The clinical course of the illness is divided into three stages: catarrhal, paroxysmal and convalescent. Unvaccinated or incompletely vaccinated infants younger than 12 months of age have the highest risk for severe and life-threatening complications and death. Complications of pertussis include apnea, pneumonia, seizure, and death. Because neither vaccination nor infection confers long-term immunity, infection of adolescents and adults is also common. Most adults and adolescents who become infected with Bordetella pertussis have been vaccinated or infected years previously. When there is residual immunity from previous infection or immunization, symptoms may be milder, such as a prolonged cough without the other classic symptoms of pertussis.

Natural History

The clinical course of the illness is divided into three stages: catarrhal, paroxysmal and convalescent. Pertussis has an insidious onset with catarrhal symptoms that are indistinguishable from those of minor respiratory tract infections. The cough, which is initially intermittent, becomes paroxysmal. In typical cases paroxysms terminate with inspiratory whoop and can be followed by posttussive vomiting. Paroxysms of cough, which may occur more at night, usually increase in frequency and severity as the illness progresses and typically persist for 2 to 6 weeks or more. The illness can be milder and the characteristic "whoop" absent in children, adolescents and adults who were previously vaccinated. After paroxysms subside, a nonparoxysmal cough can continue for 2 to 6 weeks or longer.

Shown below is a table summarizing the main findings in each stage.

Stage	Duration	Key features
Catarrhal	Usually 7-10 days; range of 4-21	- Low grade fever - Coryza - Mild occasional cough
Paroxysmal	Usually lasts 1-6 weeks, but may persist for up to 10 weeks	- Paroxysms of numerous, rapid coughs due to difficulty expelling thick mucus from the tracheobronchial tree. - Long aspiratory effort accompanied by a high-pitched "whoop" at the end of the paroxysms - Cyanosis - Vomiting and exhaustion - Paroxysmal attacks occur frequently at night, with an average of 15 attacks per 24 hours. - Paroxysmal attacks increase in frequency during the first 1-2 weeks, remain at the same frequency for 2-3 weeks, and then gradually decrease.
Convalescent	Usually 7-10 days; range of 4-21	- Gradual recovery - Less persistent, paroxysmal coughs that disappear in 2-3 weeks - Paroxysms often recur with subsequent respiratory infections for many months after the onset of pertussis.

Complications

Infants and Children

• Pertussis can cause serious and potentially life-threatening complications in infants and young children who are not fully vaccinated.

• In infants younger than 12 months of age who get pertussis, about half are hospitalized. Hospitalization is most common in infants younger than 6 months of age. Of those infants who are hospitalized with pertussis approximately:
  • 67% will have apnea
  • 23% get pneumonia
  • 1.6% will have seizures
  • 1.6% will die
  • 0.4% will have encephalopathy (as a result of hypoxia from coughing or possibly from toxin)

• Other complications can include anorexia, dehydration, difficulty sleeping, epistaxis, hernias, otitis media, and urinary incontinence. Epistaxis and secondary bacterial superinfection might also occur.

• More severe complications can include refractory pulmonary hypertension, pneumothorax, rectal prolapse, and subdural hematomas.

Adolescents and Adults

• Adolescents and adults can also develop complications from pertussis, but they are usually less severe in this older age group, especially in those who have been vaccinated.
• In one study, hospitalization rates were 0.8% for adolescents and 3% for adults with confirmed pertussis. Pneumonia was diagnosed in 2% of each group. The most common complications in another study of adults with pertussis were:
  • Weight loss (33%)
  • Urinary incontinence (28%)
  • Syncope (6%)
  • Rib fractures from severe coughing (4%)
• Other complications can include anorexia, dehydration, epistaxis, hernias, and otitis media.
• More severe complications can include encephalopathy as a result of hypoxia from coughing or possibly from toxin, pneumothorax, rectal prolapse, subdural hematomas, and seizures.

Prognosis

• Unvaccinated or incompletely vaccinated infants younger than 12 months of age have the highest risk for severe and life-threatening complications and death.

• Treatment with an effective antibiotic (erythromycin or azithromycin) shortens the infectious period but does not generally alter the outcome of the disease; however, when treatment is initiated during the catarrhal stage, symptoms may be less severe.

• Illness is generally less severe, and the typical “whoop” less frequently seen in adolescents and adults.