Pertussis (Whooping Cough) in Children
- Overview
- How Pertussis Injures the Airways
- The Three Stages of Pertussis
- Pertussis in Infants Under 6 Months
- Diagnosis
- Treatment
- Post-Exposure Prophylaxis
- DTaP Vaccine Schedule and Immunity
- Prevention in the Neonatal Period
- Complications in Children
- Key Research Papers
- Featured Videos
- Connections
Overview
Pertussis — commonly called whooping cough — is a highly contagious respiratory illness caused by Bordetella pertussis, a gram-negative coccobacillus. Despite widespread vaccination in high-income countries, pertussis remains a major global health burden: the World Health Organization estimates approximately 16 million cases per year worldwide, resulting in roughly 195,000 deaths annually, the vast majority in infants under one year of age in low-income settings.
In the United States, pertussis has resurged dramatically since the 1980s. Between 15,000 and 50,000 cases are reported each year, with periodic epidemic peaks occurring on a cyclical 3–5 year basis. This cyclical pattern reflects the waning of immunity from acellular pertussis vaccines used in the routine childhood schedule since the 1990s. Unlike the older whole-cell pertussis vaccines, acellular formulations produce fewer side effects but confer immunity that fades more rapidly — often within 4 to 12 years of the last dose.
The disease is most dangerous in infants under 6 months of age, who cannot yet complete the primary vaccine series and therefore have little or no active immunity. These youngest patients account for the overwhelming majority of pertussis-related hospitalizations and deaths in the United States.
How Pertussis Injures the Airways
Bordetella pertussis produces an array of virulence factors that work together to colonize the respiratory tract and disable host defenses. The organism attaches to ciliated respiratory epithelial cells using filamentous hemagglutinin (FHA) and pertactin, a surface adhesin. Once attached, the bacterium deploys its most destructive weapon: pertussis toxin (PT).
Pertussis toxin is an ADP-ribosyltransferase that inactivates Gi-type G-proteins in host cells. The downstream consequences are extensive: inhibitory signals to adenylyl cyclase are blocked, intracellular cyclic AMP (cAMP) rises, and a cascade of pathological effects follows — impaired phagocyte chemotaxis, reduced lymphocyte trafficking (causing the characteristic lymphocytosis), dysregulated insulin secretion, and augmented histamine sensitization. The white blood cell count in paroxysmal pertussis commonly rises to 20,000–100,000 cells per microliter with a predominance of lymphocytes, a finding so characteristic that it is considered a hallmark of the disease.
Tracheal cytotoxin — a fragment of peptidoglycan — directly kills ciliated epithelial cells, impairing mucociliary clearance. Adenylate cyclase toxin (ACT), secreted by the bacterium, further raises intracellular cAMP in phagocytes and impairs their ability to kill the organism. The combined destruction of cilia and innate immune function explains why pertussis produces such prolonged, severe coughing: the respiratory tract cannot clear secretions normally, and cough becomes the only available mechanism.
The Three Stages of Pertussis
Pertussis follows a predictable three-stage course, although the clinical presentation varies significantly with age and vaccination status.
Catarrhal Stage (1–2 weeks): The illness begins insidiously with symptoms indistinguishable from a common cold — runny nose, mild cough, and low-grade fever. This phase is the most contagious period of the illness: the bacterial load in the nasopharynx is highest, and patients are shedding organisms before the diagnosis is suspected. Paroxysmal coughing has not yet developed, so the disease goes largely unrecognized.
Paroxysmal Stage (2–6 weeks): The catarrhal symptoms fade as intense paroxysmal coughing attacks begin. A paroxysm consists of a rapid series of forceful coughs within a single exhalation, followed by a sudden, massive inspiratory effort through a partially closed glottis — producing the classic high-pitched whoop. Post-tussive vomiting is common after the prolonged exhalation. Infants, however, frequently do not produce a whoop; instead they may present with apnea — periods of breathing cessation — as the most prominent and alarming symptom. Older adolescents and adults similarly may not whoop, appearing merely to have a prolonged "cough illness."
Convalescent Stage (weeks to months): Coughing gradually diminishes over weeks but may persist or recur with subsequent respiratory infections for months. The historical name "100-day cough" reflects this prolonged convalescence, which can last three months or longer. Recurrent paroxysms triggered by subsequent viral upper respiratory infections are characteristic and can be distressing to families who believe their child has relapsed.
Pertussis in Infants Under 6 Months
Infants under 6 months of age represent the highest-risk group for severe pertussis and death. This age group is doubly vulnerable: they cannot complete the primary DTaP series (which begins at 2 months, with the second dose at 4 months and third at 6 months), and they have no significant maternal antibody protection unless their mother received Tdap during pregnancy.
The clinical presentation in young infants differs substantially from older children. The inspiratory whoop is often absent — the respiratory muscles lack the strength to generate it. Instead, apnea (cessation of breathing, sometimes lasting 30–60 seconds) and cyanosis are the presenting features that bring families to the emergency department. Bradycardia may accompany apneic episodes. Many parents and clinicians initially attribute these episodes to feeding difficulties, gastroesophageal reflux, or apparent life-threatening events (ALTEs) before pertussis is suspected.
Pneumonia is the most frequent serious complication in this age group, caused either by pertussis itself or by secondary bacterial superinfection. Pertussis encephalopathy — characterized by seizures and altered consciousness — occurs rarely but is life-threatening; it results from a combination of severe hypoxia during paroxysms and possible direct neurotoxic effects of pertussis toxin.
The most feared complication in young infants is severe pulmonary hypertension with leukostasis. Extreme lymphocytosis (WBC >100,000) can cause pulmonary leukostasis — obstruction of pulmonary capillaries by lymphocytes — resulting in pulmonary hypertension refractory to conventional therapy. Exchange transfusion or leukoreduction has been used in desperate cases to rapidly reduce the white cell burden, with variable success. This complication carries a very high case-fatality rate.
ICU admission rates exceed 50% for infants under 6 months hospitalized with pertussis. The case fatality rate for infants under 1 year is approximately 1–2% in the United States, but substantially higher in resource-limited settings.
Diagnosis
Diagnosing pertussis requires awareness of the disease at each clinical stage, since the optimal test differs by timing.
Culture: Nasopharyngeal culture on Regan-Lowe or Bordet-Gengou medium is the gold standard and the only test that provides an isolate for antimicrobial susceptibility testing. However, culture is most sensitive during the catarrhal phase, before antibiotics are given. Sensitivity drops sharply in the paroxysmal stage and after antibiotic treatment has begun. Results take 7–10 days, limiting clinical utility.
PCR: Nasopharyngeal PCR is the most sensitive and practical test during the paroxysmal phase. It detects bacterial DNA even after antibiotic treatment and is now the mainstay of diagnosis in clinical practice. Specificity is high when performed in accredited laboratories. Both culture and PCR should ideally be sent simultaneously from a nasopharyngeal aspirate or deep nasopharyngeal swab.
Serology: IgG antibody to pertussis toxin (anti-PT IgG) is elevated in convalescent disease and in late paroxysmal stage. It is most useful for diagnosing pertussis in older children and adults who present weeks into illness, when culture and PCR may be negative, and for epidemiological investigations of outbreak contacts. A single elevated anti-PT IgG in a non-recently-vaccinated individual is highly specific for recent infection.
Complete blood count: A CBC showing leukocytosis with absolute lymphocyte predominance — WBC >20,000 with lymphocytes comprising 60–80% — in a child with a prolonged cough illness is strongly suggestive of pertussis and should prompt immediate diagnostic workup and empiric treatment.
Chest X-ray: May show perihilar infiltrates ("shaggy heart" sign) or patchy consolidation when pneumonia is present, but is often normal in uncomplicated pertussis.
Treatment
The cornerstone of pertussis treatment is macrolide antibiotics, though their effect differs depending on the stage of illness at which they are given.
Azithromycin is the preferred antibiotic for all ages, including infants under 1 month (where other macrolides carry additional risks). The standard course is 5 days. For infants over 1 month and children, alternatives include erythromycin (14 days; the historical standard but associated with more gastrointestinal side effects) and clarithromycin (7 days). Trimethoprim-sulfamethoxazole (TMP-SMX) is an alternative for patients who cannot tolerate macrolides, though it is less well studied.
A critical caveat applies to erythromycin in neonates under 1 month of age: erythromycin has been associated with infantile hypertrophic pyloric stenosis (IHPS), a potentially serious complication. Azithromycin should be used preferentially in this youngest age group.
Timing of antibiotics determines their clinical benefit: when given in the catarrhal phase, antibiotics shorten the duration of illness, reduce severity, and most importantly, eliminate the organism and prevent transmission to others. When antibiotics are started during the paroxysmal phase — the point at which most patients are diagnosed — they no longer appreciably shorten the clinical course (the coughing is driven by toxin-mediated damage already done), but they are still critical for reducing contagiousness and protecting household contacts.
Supportive care is essential, especially for hospitalized infants. Key measures include supplemental oxygen for hypoxia, gentle suctioning of secretions, minimizing environmental stimulation (handling, feeding, and examination can trigger paroxysms), and maintaining adequate hydration and nutrition. Infants under 6 months with pertussis should be hospitalized for continuous cardiorespiratory monitoring.
Patients should be considered infectious until they have completed 5 days of effective antibiotic therapy, at which point they may return to school or daycare. Without antibiotic treatment, the infectious period extends for 3 weeks from the onset of paroxysms.
Post-Exposure Prophylaxis
All close contacts of a confirmed or suspected pertussis case should receive antibiotic prophylaxis, regardless of their vaccination status. This is because vaccination, while highly effective at preventing severe disease and death, does not completely prevent infection or asymptomatic carriage and transmission.
The same antibiotics and dosing regimens used for treatment are used for post-exposure prophylaxis — typically a 5-day course of azithromycin. The benefit of prophylaxis is greatest when started within 21 days of the index patient's cough onset (ideally within 7–14 days).
Priority for prophylaxis should be given to:
- Household contacts, especially those who have contact with infants under 12 months
- All household members when any member is a high-risk individual (infant, immunocompromised person, or pregnant woman in the third trimester)
- Child-care and classroom contacts of the index case
- Healthcare workers with direct patient contact who may expose vulnerable patients
Close contacts who are not up to date with pertussis vaccination should also receive the appropriate vaccine (DTaP for children, Tdap for adolescents and adults), as this provides ongoing protection even if it does not affect the current exposure window.
DTaP Vaccine Schedule and Immunity
The DTaP (diphtheria, tetanus, acellular pertussis) vaccine is administered in a 5-dose primary series: at 2, 4, and 6 months of age, a fourth dose at 15–18 months, and a fifth dose at 4–6 years (before school entry). This series provides strong initial protection, with vaccine efficacy estimated at 80–90% against typical pertussis disease in fully vaccinated children.
At age 11–12 years, a single Tdap booster (reduced-antigen content diphtheria and tetanus toxoids with acellular pertussis) is recommended by the Advisory Committee on Immunization Practices (ACIP). This booster addresses the waning immunity that occurs 4–12 years after the last DTaP dose. Without this booster, adolescents increasingly become susceptible to pertussis and serve as a reservoir for transmitting the disease to unvaccinated infants in the community.
A key limitation of acellular pertussis vaccines is that they generate primarily antibody-mediated (Th2-type) immunity, in contrast to the whole-cell pertussis vaccines (wP) used prior to the 1990s, which induced broader cellular (Th1/Th17) immunity. Studies in baboon models demonstrated that animals vaccinated with acellular pertussis cleared infection more slowly and remained colonized longer than those vaccinated with whole-cell vaccines — even while showing less clinical disease. This phenomenon — protection against symptomatic disease that wanes faster than protection against colonization and transmission — underlies the resurgence of pertussis in well-vaccinated populations and is an active area of vaccine research.
The cocooning strategy involves vaccinating all household contacts of a newborn (parents, older siblings, grandparents, caregivers) with Tdap before or shortly after the baby's birth, to create a protective ring of immune individuals around the vulnerable infant. While conceptually sound, cocooning has proven logistically difficult to implement at scale.
Prevention in the Neonatal Period
The most effective intervention available to protect newborns from pertussis is maternal Tdap vaccination during pregnancy. The current ACIP recommendation is for pregnant women to receive Tdap between 27 and 36 weeks gestation during every pregnancy, regardless of prior vaccination history.
The rationale is straightforward: maternal IgG antibodies cross the placenta in the third trimester, reaching their highest concentration at birth. An infant born to a mother vaccinated at 27–36 weeks carries a substantial antibody burden that provides passive protection during the first 2–3 months of life — precisely the window before the infant can complete enough of the primary DTaP series to develop active immunity.
A landmark UK study published in The Lancet in 2014 (Amirthalingam et al., PMID 25037990) demonstrated that maternal Tdap vaccination reduced confirmed pertussis in infants under 3 months by 91% and hospitalization by 78% compared to unvaccinated mothers. This represents the most powerful single intervention available for preventing infant pertussis.
The timing matters: vaccination at 27–36 weeks optimizes antibody transfer because the placenta actively concentrates IgG from maternal to fetal circulation in the late third trimester. Vaccination earlier in pregnancy or in the postpartum period is significantly less effective at protecting the newborn, because the window for maximal transplacental antibody transfer will have passed or not yet occurred.
Parents and grandparents who have not received Tdap within the previous 5 years should also be vaccinated before contact with a newborn, as part of a comprehensive protection strategy.
Complications in Children
While most children who contract pertussis recover fully, serious complications can occur, particularly in unvaccinated or incompletely vaccinated children and in infants.
- Pneumonia — the most common serious complication, occurring in 5–10% of reported pertussis cases. May result from direct Bordetella pertussis infection of the lung parenchyma or, more commonly, from secondary bacterial superinfection (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus). Pneumonia is the leading cause of pertussis-associated death.
- Encephalopathy — rare, occurring in approximately 1 per 100 reported cases. Manifests as seizures, altered consciousness, or focal neurological deficits. Caused primarily by severe hypoxia during prolonged paroxysms; a direct neurotoxic role of pertussis toxin has also been proposed. Prognosis is variable; some children sustain permanent neurological injury.
- Subconjunctival hemorrhage — petechial or confluent hemorrhages of the conjunctiva from the markedly elevated intrathoracic pressure generated during coughing paroxysms. The appearance is alarming to parents but typically resolves completely within 2–4 weeks without treatment.
- Hernia and rectal prolapse — prolonged, forceful coughing dramatically raises intra-abdominal pressure, which can precipitate inguinal hernia, incisional hernia rupture, or rectal prolapse. These are uncommon but important mechanical complications.
- Weight loss and failure to thrive — post-tussive vomiting occurring multiple times daily over weeks depletes caloric intake and can cause significant weight loss, particularly in infants. Nasogastric or intravenous nutrition may be required in severe cases.
- Pulmonary hypertension with leukostasis — the most feared complication in infants with extreme leukocytosis (WBC >100,000). Associated with a very high mortality rate despite aggressive intervention, including exchange transfusion and extracorporeal membrane oxygenation (ECMO).
- Death — occurs almost exclusively in young infants. In the United States, approximately 10–15 infant deaths are reported annually from pertussis, with most occurring in infants under 3 months of age who were too young to have been vaccinated.
Key Research Papers
The following peer-reviewed publications provide the evidence base for current understanding of pertussis epidemiology, pathogenesis, and prevention in children and infants.
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Crowcroft NS, Pebody RG. Recent developments in pertussis. Lancet. 2006;367(9526):1926–1936.
A comprehensive review of global pertussis epidemiology, the waning immunity phenomenon, and the public health challenge of resurgence in vaccinated populations. Essential context for understanding why cyclical outbreaks continue despite high vaccine coverage.
PubMed PMID 16765762 -
Mattoo S, Cherry JD. Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies. Clin Microbiol Rev. 2005;18(2):326–382.
A landmark review of Bordetella pertussis virulence factors — pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin, and adhesins — and their roles in disease pathogenesis. The definitive molecular reference.
PubMed PMID 15831828 -
Klein NP, Bartlett J, Rowhani-Rahbar A, Fireman B, Baxter R. Waning protection after fifth dose of acellular pertussis vaccine in children. N Engl J Med. 2012;367(11):1012–1019.
Demonstrated that protection from the fifth DTaP dose (given at 4–6 years) wanes substantially within 2–3 years after vaccination, with children vaccinated earliest showing the highest risk for pertussis during epidemic years. Foundational evidence for the waning immunity problem.
PubMed PMID 22931315 -
Amirthalingam G, Andrews N, Campbell H, et al. Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet. 2014;384(9953):1521–1528.
Prospective evaluation of the UK maternal Tdap vaccination program showing 91% vaccine effectiveness against confirmed pertussis in infants under 3 months of age. The strongest clinical evidence for maternal vaccination as a neonatal protection strategy.
PubMed PMID 25037990 -
Warfel JM, Zimmerman LI, Merkel TJ. Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model. Proc Natl Acad Sci USA. 2014;111(2):787–792.
Baboon model study demonstrating that acellular pertussis vaccine recipients, while protected from symptomatic disease, were colonized with B. pertussis and transmitted infection. Explains why vaccinated individuals can serve as silent reservoirs and why herd immunity is harder to achieve with acellular vaccines.
PubMed PMID 24277828 -
Cherry JD. Epidemic pertussis in 2012 — the resurgence of a vaccine-preventable disease. N Engl J Med. 2012;367(9):785–787.
Editorial analysis of the 2012 US pertussis epidemic (over 48,000 cases, the highest count since 1955). Attributes resurgence to waning immunity from acellular vaccines rather than vaccine hesitancy, reshaping public health messaging and research priorities.
PubMed PMID 22931320 -
Surridge J, Segedin E, Grant CC. Pertussis requiring intensive care. Arch Dis Child. 2007;92(11):970–975.
Retrospective case series describing the clinical course of infants with pertussis requiring PICU admission, including leukocytosis, apnea, pneumonia, and pulmonary hypertension. Documents the 50%+ ICU admission rate and high case fatality risk in the youngest infants.
PubMed PMID 17405852 -
Halperin SA, Wang EE, Law B, et al. Epidemiological features of pertussis in hospitalized patients in Canada, 1991–1997: report of the Immunization Monitoring Program — Active (IMPACT). Clin Infect Dis. 1999;28(6):1238–1243.
Multicenter Canadian surveillance of hospitalized pertussis cases, documenting age distribution of complications, pneumonia prevalence, and outcomes across the pre-adolescent and infant populations.
PubMed PMID 10451150 -
Bisgard KM, Pascual FB, Ehresmann KR, et al. Infant pertussis: who was the source? Pediatr Infect Dis J. 2004;23(11):985–989.
Identified the source of pertussis transmission to hospitalized infants: parents (55%) were the most common source, followed by siblings (16%) and grandparents (5%). Supports the cocooning strategy and maternal vaccination as the most impactful prevention approaches.
PubMed PMID 15545852 -
Masseria C, Martin CK, Krishnarajah G, Bhattacharya R, Buikema AR, Tan TQ. Incidence and burden of pertussis among infants less than 1 year of age. Pediatr Infect Dis J. 2017;36(3):e54–e61.
US insurance-claims analysis quantifying the real-world clinical and economic burden of pertussis in the first year of life, including hospitalization rates, complications, and healthcare costs. Underscores the public health importance of maternal vaccination.
PubMed PMID 27636954 -
Tiwari T, Murphy TV, Moran J; National Immunization Program, CDC. Recommended antimicrobial agents for the treatment and postexposure prophylaxis of pertussis: 2005 CDC guidelines. MMWR Recomm Rep. 2005;54(RR-14):1–16.
CDC guidelines establishing azithromycin, erythromycin, and clarithromycin as the preferred agents for treatment and prophylaxis, with specific dosing recommendations by age group and the IHPS warning for erythromycin in neonates under 1 month.
PubMed PMID 16372576 -
Pertussis (Whooping Cough) in infants and children — additional clinical references:
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