Pertussis, also known as whooping cough, is a highly contagious acute respiratory illness caused by Bordetella pertussis. The infection primarily targets the mucosal lining of the respiratory tract and is characterized by a prolonged paroxysmal cough, often accompanied by a high-pitched “whoop” sound during gasping inhalation following coughing fits. The disease has a global distribution and occurs year-round, with seasonal peaks in some regions.
Pertussis most commonly affects infants and young children, particularly those who are unvaccinated or incompletely vaccinated, but it can also occur in adolescents and adults, especially as vaccine-induced immunity wanes. Adults and older children may present with atypical or milder symptoms, which contributes to underdiagnosis and facilitates ongoing community transmission.
Transmission occurs via respiratory droplets expelled during coughing or sneezing by infected individuals. The incubation period typically ranges from 7 to 10 days but can extend up to 21 days. The disease progresses through three stages: the catarrhal stage (mild respiratory symptoms), the paroxysmal stage (severe coughing spells), and the convalescent stage (gradual recovery). During the paroxysmal phase, patients may experience vomiting, exhaustion, or apnea, particularly in infants.
Although vaccination with diphtheria-tetanus-acellular pertussis (DTaP) or tetanus-diphtheria-acellular pertussis (Tdap) vaccines has significantly reduced disease incidence in many countries, immunity wanes over time, and booster doses are necessary to maintain population-level protection. Outbreaks still occur, even in highly vaccinated populations, due to factors such as suboptimal vaccine coverage, declining immunity, and asymptomatic carriers.
Complications of pertussis can include pneumonia, seizures, encephalopathy, and death, particularly in infants under six months of age. Diagnosis is confirmed through clinical suspicion supported by polymerase chain reaction (PCR) testing, culture from nasopharyngeal specimens, or serology in later stages. Early treatment with macrolide antibiotics, such as azithromycin or clarithromycin, can reduce symptom severity and infectiousness but may have limited effect once the paroxysmal phase has begun.
Epidemiology and Prevalence
Pertussis remains endemic in many parts of the world despite widespread immunization efforts. According to the World Health Organization (WHO), over 151,000 laboratory-confirmed cases were reported globally in 2018. However, the actual burden is significantly higher, with approximately 24 million cases and 160,700 deaths annually among children under five years of age worldwide, particularly in low-resource settings where under-diagnosis and under-reporting are common.
In the United States, reported pertussis cases have shown notable fluctuations. In 2022, 3,044 cases were recorded, increasing to 7,063 in 2023. By mid-April 2025, over 8,000 cases had been reported—twice the number during the same period in 2024—with projected totals nearing 70,000 by year-end. Historically, prior to the introduction of the whole-cell pertussis vaccine in the 1940s, annual case counts exceeded 150,000. This figure declined to fewer than 5,000 cases annually by 1970. Age-specific incidence remains highest in infants under one year (23.16 per 100,000 in 2023), while adults over 20 years exhibit lower rates (1–2 per 100,000).
The European Union and European Economic Area (EU/EEA) recorded over 25,000 pertussis cases in 2023. In the first quarter of 2024 alone, more than 32,000 cases were reported, mirroring previous epidemic peaks such as in 2016 (41,000 cases) and 2019 (34,000 cases). Between 2023 and early 2024, nearly 60,000 cases were reported across the region, with 19 confirmed deaths—11 in infants and 8 in older adults. Surveillance data indicate that infants under one year have the highest incidence across most countries. However, in some areas, adolescents aged 10–19 years represented the group with the highest rates.
Globally, reported pertussis cases declined to a low of 29,623 in 2021, largely due to pandemic-related disruptions, before rising to 63,024 in 2022 and continuing to increase through 2023. Several countries in Latin America have reported significant outbreaks. In 2023, Peru recorded 144 deaths and a case fatality rate of 4.2%. Bolivia reported 693 cases, Argentina documented 605 (primarily in Salta), and Brazil confirmed 2,954 cases and 12 deaths by late 2024.[13] Afghanistan also experienced a substantial increase in reported cases, rising from 108 in 2021 to 1,531 in 2023, suggesting gaps in immunization coverage and disease surveillance.
Infants under six months of age represent the most vulnerable demographic, accounting for the highest morbidity and mortality. Nearly all pertussis-related deaths occur in this age group, prior to completion of the primary vaccine series. Adolescents and adults constitute an increasing proportion of reported cases due to waning immunity post-acellular vaccination. These individuals often serve as reservoirs of infection, transmitting the disease to unvaccinated or partially vaccinated infants.
Global coverage for the first and third doses of the diphtheria–tetanus–pertussis (DTP) vaccine fell to 87% and 81%, respectively, in 2021 due to disruptions from the COVID-19 pandemic. By 2023, coverage partially rebounded to approximately 90% and 88%. However, regional disparities remain significant. In the United States, pertussis vaccination coverage among kindergarten-aged children declined from pre-pandemic levels of approximately 95% to 92.3% in the 2023–2024 academic year, with rising exemption rates contributing to localized reductions in herd immunity.
Vaccine-derived immunity—particularly from acellular formulations—declines over time, with effectiveness decreasing by an estimated 2–10% annually. This contributes to increasing susceptibility among older children, adolescents, and adults.
In the United Kingdom, both England and Scotland experienced significant outbreaks in 2024. Scotland reported 5,270 laboratory-confirmed cases by mid-July 2024, a sharp increase from just 73 cases in 2023. Adults over 15 years accounted for 59.8% of cases, and multiple infant deaths were confirmed.
In the United States, as of April 2025, 8,485 pertussis cases had been reported—double the number during the same period in 2024. Multiple fatalities in infants and a child have raised concern about the possibility of one of the largest national outbreaks in decades.
Causes and Transmission
Pertussis, commonly known as whooping cough, is a highly contagious respiratory disease caused by the bacterium Bordetella pertussis. Transmission dynamics are influenced by biological characteristics of the pathogen, human behavior, and environmental factors.
Bordetella Pertussis Bacterium
Bordetella pertussis is a fastidious, non-motile, aerobic Gram-negative coccobacillus. Its pathogenicity stems from a combination of virulence factors, most notably:
- Pertussis toxin (PT): Disrupts signal transduction in host cells and suppresses immune responses.
- Filamentous hemagglutinin (FHA): Mediates adhesion to respiratory epithelium.
- Adenylate cyclase toxin (ACT): Inhibits phagocytic activity of immune cells.
- Tracheal cytotoxin (TCT): Damages ciliated epithelial cells, impairing mucus clearance.
Upon inhalation, the bacterium adheres to the ciliated epithelial cells of the upper respiratory tract. The subsequent inflammation and cytotoxic effects lead to the hallmark paroxysmal coughing and prolonged illness. Notably, B. pertussis is strictly human-specific and lacks an animal reservoir.
B. pertussis is extremely sensitive to desiccation, UV light, and disinfectants, and typically survives only a few hours outside the host. This limits the role of fomites in transmission.
Modes of Transmission
The disease spreads primarily via respiratory droplets produced when an infected individual coughs, sneezes, or talks. Transmission occurs during the catarrhal stage, when symptoms mimic a common cold and bacterial load is highest. The infectious period usually extends from 7 days after exposure to approximately 21 days post-symptom onset if untreated.
- Droplet radius: Transmission is generally confined to a 1–2 meter radius.
- Airborne spread (aerosols): Though droplet transmission is predominant, aerosol spread in poorly ventilated settings has been documented during outbreaks.
According to the WHO, 90–100% of susceptible household contacts of a pertussis case will contract the infection in the absence of vaccination or prophylactic antibiotics.
Risk Factors
Certain population groups face increased risk due to biological vulnerability or environmental exposure:
- Infants under 6 months: They account for the majority of severe cases and fatalities. In the U.S., infants <2 months (who are too young to be vaccinated) represent more than 80% of pertussis-related deaths.
- Adolescents and adults: Waning immunity post-vaccination or natural infection renders this group a significant reservoir for transmission, often with atypical or milder symptoms.
- Unvaccinated populations: Outbreaks are often clustered in areas with low immunization rates due to vaccine hesitancy or access issues.
- Healthcare workers and caregivers: Occupational exposure places these individuals at elevated risk, particularly in neonatal and pediatric care settings.
- Households and schools: Close-contact environments facilitate rapid spread, especially in multi-child households or daycare centers.
In 2010, California experienced its worst pertussis outbreak in over 60 years, with over 9,000 cases and 10 infant deaths. Investigations revealed that:
- 83% of cases under 6 months were hospitalized.
- Many adult caregivers were asymptomatic or mildly symptomatic carriers.
- Waning immunity in adolescents (6–10 years post-DTaP) contributed to the outbreak.
Symptoms and Clinical Presentation
Pertussis develops in distinct stages, each with specific clinical features that reflect the progression of the infection. The presentation varies from mild respiratory symptoms to severe coughing episodes with potential complications.
Early Stage Symptoms
This initial phase, also known as the catarrhal stage, lasts about one to two weeks. Patients experience symptoms similar to a common cold: runny nose, mild cough, sneezing, low-grade fever, and watery eyes.
The cough is usually mild and non-specific during this period. Because these symptoms are nonspecific, pertussis can often be mistaken for an upper respiratory infection at this stage.
Paroxysmal Stage Features
The paroxysmal stage follows the catarrhal phase and can last four to six weeks. It is characterized by intense, repetitive coughing fits that end with a high-pitched “whooping” sound during inhalation.
Coughing paroxysms may cause vomiting, cyanosis, or exhaustion. The frequency and severity of the cough can lead to complications, especially in infants, such as pneumonia or rib fractures.
Convalescent Phase Characteristics
This final phase extends over several weeks to months. Coughing episodes gradually decrease in frequency and severity but may still be triggered by respiratory irritants.
Other symptoms, such as fatigue and weakness, persist during recovery. Though the cough lessens, patients remain vulnerable to secondary respiratory infections during this time.
Diagnosis of Pertussis
Diagnosis of pertussis (whooping cough) involves integrating clinical judgment with targeted laboratory investigations to confirm the presence of Bordetella pertussis, particularly in the early stages when symptoms may overlap with other respiratory illnesses.
Clinical Assessment
Pertussis is initially suspected based on its distinctive clinical presentation, especially in the paroxysmal stage, which typically begins 1–2 weeks after the onset of symptoms.
- Early (Catarrhal) Phase: Mild symptoms mimic the common cold—low-grade fever, nasal congestion, and dry cough—making early diagnosis challenging.
- Paroxysmal Phase: This is characterized by repetitive, forceful coughing fits often ending in a “whooping” sound during inspiration. Post-tussive vomiting and cyanosis are common, especially in infants.
- Convalescent Phase: Cough gradually improves but may last several weeks to months, especially without treatment.
Infants, especially those under one year of age, may present with apnea, cyanosis, or seizures rather than a classic cough. In such cases, the absence of the typical paroxysmal cough may delay diagnosis. Adolescents and adults often experience a prolonged, nonproductive cough without fever or whoop, leading to frequent misdiagnosis as bronchitis or viral infection.
Laboratory Testing Methods
Laboratory testing is used to confirm pertussis in suspected cases, particularly during outbreaks or when clinical findings are inconclusive. The three principal methods for confirmation are bacterial culture, polymerase chain reaction (PCR), and serology.
Culture is considered the reference standard but has limited sensitivity, particularly after the initial two weeks of symptoms. It requires nasopharyngeal specimens collected using Dacron or polyester swabs, and the organism must be grown on specialized media such as Regan–Lowe agar. Culture sensitivity ranges from 30 to 60 percent and declines with antibiotic use or improper specimen handling.
PCR testing detects Bordetella pertussis DNA and is more sensitive than culture, especially during the early stages of illness. It is most effective when performed within the first three weeks of cough onset. PCR assays often target the IS481 insertion sequence, which is present in multiple copies in the B. pertussis genome, increasing sensitivity but occasionally leading to cross-reactivity with B. holmesii.
Serologic testing measures immunoglobulin G (IgG) antibodies to pertussis toxin and is particularly useful later in the disease course or when PCR and culture results are negative. It is generally applied in individuals aged over one year and in cases with a cough duration exceeding three weeks. The interpretation of serologic tests may vary due to a lack of standardized international assays.
Proper specimen collection is critical to the accuracy of both culture and PCR. Nasopharyngeal swabs or aspirates should be collected as early as possible, ideally within 21 days of symptom onset, to maximize diagnostic yield.
Differential Diagnosis
The clinical presentation of pertussis overlaps with several other respiratory and non-respiratory conditions, complicating diagnosis in the absence of laboratory confirmation. Diseases commonly considered in the differential diagnosis include viral respiratory infections such as influenza, respiratory syncytial virus (RSV), and adenovirus. Bacterial infections, including Mycoplasma pneumoniae and Chlamydia pneumoniae, may also produce similar symptoms.
Asthma, especially in children, may present with paroxysmal coughing. In older individuals, chronic cough due to gastroesophageal reflux disease (GERD) or allergic rhinitis may mimic pertussis. Tuberculosis should also be considered in cases of chronic cough, particularly in endemic regions.
A comprehensive history, including vaccination status and exposure to known cases, is essential to guide testing and narrow the differential diagnosis. In settings with increased community transmission, clinicians may initiate empiric treatment based on clinical suspicion prior to laboratory confirmation.
Treatment and Management
Effective treatment of pertussis involves targeted antibiotic use, supportive care to relieve symptoms, and monitoring for complications that may require further intervention. Each aspect plays a critical role in limiting infection spread and aiding patient recovery.
Antibiotic Therapy
Antibiotic treatment is most effective when initiated during the catarrhal stage, before the onset of paroxysmal coughing. The primary objective of antibiotic therapy is to eliminate Bordetella pertussis from the respiratory tract, thereby reducing transmission. Clinical improvement in symptoms may be modest if treatment is initiated after the paroxysmal phase has begun.
The recommended first-line agents are macrolide antibiotics. Azithromycin is typically administered for five days, while clarithromycin and erythromycin are given for seven and 14 days, respectively. For patients with macrolide intolerance or contraindications, trimethoprim-sulfamethoxazole is an alternative.
Antibiotic prophylaxis is also recommended for close contacts of confirmed cases, particularly those at high risk for severe illness, including infants, pregnant women, and individuals with pre-existing respiratory conditions.
Supportive Care
Supportive care remains the mainstay of treatment in patients with established paroxysmal symptoms. It focuses on minimizing discomfort, maintaining hydration and nutrition, and managing respiratory symptoms. Cough suppressants and bronchodilators are generally not effective and are not routinely recommended.
Patients, particularly infants and young children, benefit from a calm environment to reduce coughing stimuli. Nutritional support is critical, as coughing episodes may interfere with feeding. In some cases, nasogastric feeding may be required. Ensuring adequate hydration is essential, especially in patients with frequent vomiting.
Oxygen supplementation and humidified air may be used in patients with hypoxemia or respiratory distress. In severe cases, particularly in infants under six months of age, hospitalization is often necessary. Apnea, cyanosis, and feeding intolerance are common indications for inpatient care.
Potential Complications
Pertussis can result in a range of complications, particularly in infants and unvaccinated individuals. The most frequent complication is secondary bacterial pneumonia, which may require empiric or targeted antibiotic therapy. Neurological complications, such as seizures or encephalopathy, though rare, can occur due to hypoxia or toxin-mediated effects and warrant immediate medical evaluation.
Additional complications include rib fractures from intense coughing, otitis media, urinary incontinence, and weight loss due to prolonged feeding difficulties. In infants under six months, apnea and respiratory failure are common and may necessitate mechanical ventilation.
According to World Health Organization (WHO) estimates, pertussis-related complications contribute significantly to global pediatric mortality, with the majority of deaths occurring in infants who are either too young to be vaccinated or have incomplete immunization status
Close clinical monitoring is advised in high-risk populations throughout the course of illness. Patients should be assessed for signs of respiratory fatigue, dehydration, and secondary infection. In severe cases, pediatric intensive care may be required.
Prevention and Vaccination
Prevention of pertussis is primarily achieved through routine immunization, timely booster vaccinations, and maternal immunization during pregnancy. While antibiotics play a role in post-exposure prophylaxis, vaccination remains the most effective strategy for reducing disease incidence, severity, and mortality, particularly in infants.
Vaccination Schedules
Pertussis vaccines are administered in combination formulations, typically as diphtheria-tetanus-acellular pertussis (DTaP) for infants and young children, and as tetanus-diphtheria-acellular pertussis (Tdap) for adolescents and adults.
The World Health Organization (WHO) and national immunization programs, including the U.S. Centers for Disease Control and Prevention (CDC), recommend a 5-dose series for infants and children:
- 2 months
- 4 months
- 6 months
- 15–18 months
- 4–6 years
This schedule induces early protective immunity during the most vulnerable period of life.
A single booster dose of Tdap is recommended at 11–12 years of age to counteract waning immunity from the childhood series. Adults who did not receive Tdap in adolescence should receive a catch-up dose, particularly those in close contact with infants.
To protect neonates before their first immunizations, Tdap is recommended during each pregnancy, ideally between 27 and 36 weeks of gestation. This practice facilitates transplacental transfer of maternal antibodies, providing passive immunity to the newborn.
Effectiveness of Vaccines
The acellular pertussis (aP) vaccines, introduced in the 1990s to replace the whole-cell versions (wP), have a favorable safety profile but demonstrate shorter-lasting immunity. While DTaP and Tdap are effective in preventing severe disease, vaccine-induced immunity wanes significantly within 4–12 years after the last dose.
- DTaP vaccine effectiveness: Estimated at 80–90% within the first year after the final dose.
- Tdap vaccine effectiveness: Approximately 70–85% initially, but declines to 30–40% within four years.
Despite reduced long-term immunity, vaccination continues to provide critical protection against complications, hospitalization, and death—particularly among infants and the immunocompromised.
Booster Recommendations
Waning immunity necessitates regular booster doses to maintain population-level protection and reduce transmission. Current guidelines include:
- Adolescents: One Tdap booster at 11–12 years.
- Pregnant Women: Tdap during each pregnancy, regardless of prior vaccination history.
- Adults: One-time Tdap booster, followed by Td (tetanus-diphtheria) boosters every 10 years.
- Healthcare Workers and Caregivers of Infants: Strongly encouraged to be up to date with Tdap to prevent nosocomial and household transmission.
Pertussis in Special Populations
Pertussis affects various groups differently, with specific risks and preventive needs. Age, immune status, and pregnancy alter the disease severity and management approaches.
Infants and Young Children
Infants under six months of age are at the highest risk for severe complications from pertussis, including pneumonia, seizures, and death. Early symptoms in this age group are often nonspecific, which can complicate timely diagnosis. Hospitalization is frequently required, particularly for infants younger than three months. Although vaccination with the diphtheria, tetanus, and acellular pertussis (DTaP) vaccine beginning at two months of age provides substantial protection, immunity may decline over time. To reduce transmission risk, vaccination of close contacts—referred to as the cocooning strategy—is recommended. Antibiotic therapy is essential both for reducing disease severity and for limiting further spread in susceptible populations.
Pregnant Women
Pertussis infection during pregnancy poses significant risks to both the mother and the neonate. To mitigate these risks, maternal immunization with the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine is recommended during each pregnancy, preferably between 27 and 36 weeks of gestation. This strategy facilitates the transplacental transfer of maternal antibodies, providing passive immunity to the newborn during the early months of life, prior to initiation of the primary vaccination series.
In cases where pertussis is suspected during pregnancy, prompt administration of appropriate antibiotic therapy is advised to reduce disease severity and transmission. Due to immunological and physiological changes associated with pregnancy, clinical symptoms may be atypical or progress rapidly; therefore, close monitoring of affected individuals is warranted.
Adolescents and Adults
Immunity conferred by childhood pertussis vaccination wanes over time, rendering adolescents and adults susceptible to infection. In these age groups, pertussis frequently presents as a persistent, nonspecific cough, which can lead to underdiagnosis and contribute to ongoing transmission, particularly within household settings.
To reduce the risk of infection and secondary transmission, a booster dose of the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine is recommended for adolescents and adults, particularly those in close contact with infants or working in healthcare environments. Diagnosis in these populations is often delayed due to atypical clinical features.
Administration of macrolide antibiotics remains the standard treatment and is effective in reducing contagiousness. Increasing awareness and adherence to vaccination recommendations in these groups are essential for controlling pertussis outbreaks and protecting high-risk individuals.