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Potentially life-threatening emergency
Infant pertussis
Other Resources UpToDate PubMed
Potentially life-threatening emergency

Infant pertussis

Contributors: Eric Ingerowski MD, FAAP, Paritosh Prasad MD
Other Resources UpToDate PubMed


This summary discusses infant / neonatal patients. Pertussis in older patients is discussed separately.

Pertussis, or whooping cough, is a serious, life-threatening, highly contagious toxin-mediated infectious disease caused by the gram-negative bacterium Bordetella pertussis. While pertussis is found all over the world and can be seen in all age ranges, it is more commonly seen in developing countries. Pertussis is particularly concerning when it occurs in young infants as they lack protective immunity and their morbidity and mortality are high.

Bordetella pertussis infection primarily involves the upper respiratory tract and presents in 3 distinct phases of illness. The illness begins with a catarrhal phase that lasts for about 1-2 weeks and consists of a mild, nonspecific cough, runny nose, and low-grade fever, identical to many upper respiratory viral infections (URIs). Of particular concern, young infants may experience apnea during this phase and present with a brief resolved unexplained event (BRUE), formerly known as an apparent life-threatening event (ALTE).

The paroxysmal stage begins with a progressively severe, uncontrollable cough that occurs in "fits" that are often proceeded by the classic "whoop" as the infant attempts to take a breath. These fits of coughing occur multiple times a day and are often accompanied by cyanosis or a color change as well as post-tussive emesis. This phase can last for over 3 months, giving pertussis the nickname of "the hundred day cough." During this time, the infant may progressively tire and develop life-threatening complications such as pneumonia, respiratory failure, and pneumothoraces as well as become severely dehydrated and malnourished. Infants may also develop seizures, and over 1% will die.

The final phase, known as the convalescent stage, includes a gradual resolution of the cough and can last for several weeks. Infants remain at higher risk for other respiratory infections during this phase.

Infants younger than 6 months are at higher risk of getting pertussis as they lack protective antibodies. This is particularly true in developing nations where pregnant individuals are not given the Tdap (tetanus, diphtheria, and pertussis) vaccine during pregnancy (providing passive antibody transfer to the fetus) and overall pertussis vaccination rates are low.

Atypical presentations can occur in very young infants or those who have been partially vaccinated. This may present as a shortened or absent catarrhal stage followed by gagging and vomiting. It may also present as a wheezy cough similar to bronchiolitis.

Prior infection with B. pertussis does not prevent future infections with B. pertussis.


A37.90 – Whooping cough, unspecified species without pneumonia

27836007 – Pertussis

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Differential Diagnosis & Pitfalls

  • Influenza – More of a sudden onset with higher fevers and gastrointestinal (GI) complaints.
  • Chlamydophila pneumoniae pneumonia – Often presents with purulent conjunctivitis.
  • Adenovirus infection – Usually with higher fever, sore throat, and conjunctivitis.
  • Respiratory syncytial virus infection (RSV) – May have more lower tract respiratory findings such as wheeze and rale on exam.
  • Common cold
  • Cystic fibrosis – Consider if patient has more of a prolonged cough, failure to thrive, or prolonged diarrhea / loose stools.
  • Mycoplasma pneumonia
  • Croup – More of a barky cough that is typically much worse at night.
  • Streptococcus pneumoniae pneumonia
  • Viral pneumonia
  • Tuberculosis
  • Intussusception – Usually lacks a cough, and infant may pull up legs during bouts of abdominal pain and pass bloody stools.
  • Asthma – Recurrent history of wheezing or coughing with URIs or following other triggers.
  • Foreign body aspiration

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Last Reviewed:09/28/2017
Last Updated:01/09/2023
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Potentially life-threatening emergency
Infant pertussis
A medical illustration showing key findings of Infant pertussis (Paroxysmal Stage) : Vomiting, Cyanosis, Diaphoresis, Paroxysmal cough
Copyright © 2024 VisualDx®. All rights reserved.