The genus Bordetella encompasses several bacterial species, but Bordetella pertussis is the primary concern for human health, causing Pertussis, commonly known as Whooping Cough. This highly contagious respiratory disease affects individuals of any age. While often perceived as a childhood illness, adolescents and adults contract the infection and frequently serve as reservoirs that unknowingly spread the bacteria. Early diagnosis and prompt intervention are necessary to prevent severe outcomes, particularly in infants.
The Bordetella Bacteria and How It Infects
Bordetella pertussis is a small, Gram-negative, aerobic coccobacillus that specifically targets the ciliated cells lining the respiratory tract. The infection begins when the bacteria are inhaled and utilize specialized surface structures, known as adhesins, to anchor securely to the cilia. Proteins such as filamentous hemagglutinin and pertactin are instrumental in this initial attachment.
Once colonized, the bacteria multiply and release toxins that drive the severe symptoms of the disease. Pertussis Toxin (PT) enters host cells and interferes with cell signaling pathways, diminishing the body’s local immune response. Tracheal Cytotoxin (TCT), a fragment of the bacterial cell wall, is toxic to the ciliated epithelial cells.
The TCT paralyzes and kills these ciliated cells, which normally sweep mucus and debris out of the lungs. This destruction allows secretions to build up in the airways, triggering the forceful, uncontrollable coughing fits that characterize the illness. The combined action of the toxins and inflammation leads to the prolonged clinical course of Whooping Cough.
Recognizing the Stages of Whooping Cough
The clinical progression of Pertussis is divided into three sequential stages, following an incubation period averaging seven to ten days. The initial phase is the Catarrhal stage, which usually lasts one to two weeks and is often mistaken for a common cold. Symptoms include a runny nose, sneezing, mild cough, and sometimes a low-grade fever, making diagnosis difficult during this highly contagious period.
Next, the Paroxysmal stage begins, marked by the onset of severe, rapid, and consecutive coughing fits. During these episodes, the patient struggles to breathe, often leading to a forceful inhalation that creates the characteristic high-pitched “whoop” sound. These violent spasms can be so intense that they cause post-tussive vomiting, exhaustion, or temporary lack of oxygen, sometimes resulting in a bluish tint to the skin.
The Paroxysmal stage can persist for one to six weeks before the final phase, the Convalescent stage, begins. This recovery period is characterized by a gradual decrease in the frequency and severity of the coughing fits. A residual cough can linger for weeks or months, and subsequent respiratory infections may temporarily re-trigger the paroxysmal coughing. Diagnosis is confirmed using a nasopharyngeal swab tested via Polymerase Chain Reaction (PCR) to detect the bacteria’s genetic material.
Transmission, Risk, and Serious Complications
Pertussis is highly contagious and spreads through airborne droplets released when an infected person coughs or sneezes. Transmission occurs easily through close contact, and the infection is most communicable during the Catarrhal stage and the first two weeks of the Paroxysmal stage. Individuals who have not completed their vaccination series or whose immunity has waned are susceptible to the disease.
Infants under twelve months of age face the highest risk of severe illness and death, as they are too young to have completed the primary vaccination series. In this age group, the typical whoop may be absent; the primary sign of infection can be periods of apnea, or cessation of breathing. Approximately half of all infected infants under one year old require hospitalization for supportive care.
Serious complications in infants include pneumonia and neurological issues such as seizures and hypoxic encephalopathy (brain damage resulting from lack of oxygen). Older children and adults generally experience milder illness but can still suffer complications like syncope, sleep disturbance, rib fractures from forceful coughing, and weight loss due to vomiting.
Treatment and Preventing Future Infection
Treatment
The primary goal of medical intervention for Pertussis is to eliminate the bacteria quickly to prevent transmission to others. Macrolide antibiotics, such as azithromycin, are the preferred first-line treatment for both confirmed cases and for post-exposure prophylaxis in close contacts. Treatment is most effective at reducing the severity of symptoms and shortening the duration of illness if started early, ideally during the Catarrhal stage.
Antibiotics given later in the course of the disease may not alter the intensity or length of the cough, which is toxin-mediated, but they remain necessary to stop the patient from spreading the bacteria. Supportive care is administered to manage the severe symptoms, including maintaining hydration, providing oxygen therapy for infants with apnea, and reducing environmental triggers that initiate coughing fits. Patients are considered non-infectious after completing five full days of appropriate antibiotic treatment.
Prevention
Vaccination remains the most effective strategy for preventing Pertussis, with different formulations used depending on the age of the recipient. Infants and young children receive the Diphtheria, Tetanus, and acellular Pertussis (DTaP) vaccine as a series of five shots. Older children, adolescents, and adults receive the Tetanus, Diphtheria, and acellular Pertussis (Tdap) booster, which is also recommended for every pregnancy between 27 and 36 weeks’ gestation.
This maternal Tdap dose allows protective antibodies to pass through the placenta to the fetus, providing passive immunity to the newborn until they are old enough for their first vaccination. Although Tdap vaccination of close family members, known as “cocooning,” was once a common recommendation, it is now known that vaccinated individuals can still contract and transmit the bacteria. Therefore, the focus has shifted to maximizing protection through maternal vaccination and timely childhood immunizations.