Whooping cough is a bacterial infection of the airways that can make a person cough hard enough to vomit, crack a rib, or stop breathing. It is caused by Bordetella pertussis, a bacterium that attaches to the tiny hair-like structures lining the respiratory tract and releases toxins that damage them. The illness moves through three stages — catarrhal, paroxysmal, and convalescent — and treatment centers on antibiotics, supportive care, and in severe cases, hospital monitoring.
What Is Bordetella Pertussis?
Bordetella pertussis is a gram-negative bacterium that infects only humans. It spreads through respiratory droplets when an infected person coughs or sneezes near others. The bacteria attach to cilia — the microscopic sweeping hairs that line the airways — and produce several toxins that paralyze those cilia and inflame the tissue beneath them.
Once the cilia stop working, mucus and debris build up in the airways. The body’s only remaining way to clear them is forceful coughing. That is why the cough of pertussis is so violent and so persistent. The damage is not caused by the bacteria spreading through the bloodstream. It is caused by toxins acting locally in the respiratory tract.
Pertussis is sometimes called “the 100-day cough” because symptoms can linger for weeks or months, even after the bacteria are gone. The cough outlasts the infection because the cilia take a long time to regrow.
How Does Pertussis Spread?
Pertussis spreads person to person through airborne droplets. You do not need direct contact. Being in the same room as someone who is coughing can be enough.
The contagious period matters. A person with pertussis is most contagious during the first stage — the catarrhal stage — before the distinctive cough appears. At that point, symptoms look like an ordinary cold. This is one reason outbreaks are hard to contain. People spread the bacteria before anyone realizes what it is.
Contagiousness generally lasts from about the start of symptoms until roughly three weeks after the coughing spells begin, though it drops once a person has been on appropriate antibiotics for several days. That window is why public health guidance emphasizes early testing and treatment in household and close-contact settings.
Some people carry and transmit the bacteria with mild or no symptoms. Adults whose immunity has faded are a common source of infection for infants, who are the most vulnerable group.
What Are the Symptoms of Bordetella Pertussis?
Symptoms change depending on the stage of illness. Early on, pertussis looks like a common cold. Later, it becomes a distinctive coughing illness.
Common symptoms across the illness include:
- A runny nose and mild cough in the early days
- Severe coughing spells that come in bursts
- A “whooping” sound when gasping for air after a coughing fit, more common in unvaccinated children
- Vomiting after coughing
- Exhaustion after coughing episodes
- Difficulty catching your breath
Not everyone whoops. Infants may not whoop at all. Instead, they may gag, turn blue, or briefly stop breathing — a condition called apnea. That is a medical emergency.
Adults often have a milder version. They may cough for weeks without realizing they have pertussis. Some describe it as a cough that will not go away, worse at night, sometimes severe enough to interfere with sleep or cause vomiting.
What Are the Three Stages of Whooping Cough?
Pertussis follows a predictable pattern in three stages. The timeline varies from person to person, but the sequence is consistent.
Stage 1: Catarrhal stage. This stage lasts roughly one to two weeks. Symptoms resemble a cold — runny nose, sneezing, low fever, and a mild cough. This is when a person is most contagious. Antibiotics are most effective here, but the illness is rarely diagnosed this early because it looks like so many other things.
Stage 2: Paroxysmal stage. This is the most severe phase, typically lasting one to six weeks, though it can run longer. Coughing fits become violent and uncontrollable. A person may cough repeatedly without a breath, then gasp for air, which produces the whooping sound. Vomiting after coughing is common. Between coughing fits, most people feel relatively normal.
Stage 3: Convalescent stage. The cough gradually fades over two to three weeks, though it can last longer. Coughing fits become less frequent and less severe. A lingering cough can persist for months, especially with any new respiratory infection.
These timelines are general. Infants, older adults, and people with weakened immune systems may have different patterns. Some vaccinated people have a milder illness that does not follow the classic three-stage course.
How Is Pertussis Diagnosed?
Diagnosis relies on a clinical exam plus laboratory testing. Because early symptoms mimic a cold, doctors often suspect pertussis when a cough lasts longer than expected or when there has been known exposure.
Common tests include a nasopharyngeal swab or aspirate — a sample taken from the back of the nose and throat — sent for polymerase chain reaction (PCR) testing. PCR detects bacterial DNA and is generally the preferred method in the early weeks of illness. A blood test measuring antibodies may be used later, though its usefulness depends on timing and whether the person has been vaccinated.
Testing is most reliable early in the illness. Once the coughing has been present for several weeks, the bacteria may no longer be detectable even if the person clearly had pertussis. That does not mean the diagnosis was wrong. It means the test window had passed.
How Is Bordetella Pertussis Treated?
Antibiotics are the main treatment. They can reduce how long a person is contagious and may shorten symptoms if started early — ideally during the catarrhal stage. Once the paroxysmal stage is underway, antibiotics are less likely to change the course of the cough, but they are still given to stop spread to others.
Macrolide antibiotics are the standard first-line treatment. Azithromycin, clarithromycin, and erythromycin are commonly used. For people who cannot take macrolides, alternatives exist, though guidance differs by age and situation. Antibiotic choice and dosing should always come from a clinician, not from general information.
Supportive care matters too. Rest, fluids, and humidified air can ease symptoms. Avoiding irritants like smoke helps. Because coughing fits can be exhausting and can cause vomiting, small frequent meals may be easier than large ones.
Infants and young children often need hospital care. Apnea, poor feeding, and low oxygen levels are reasons for close monitoring. In severe cases, oxygen support and intravenous fluids are used.
No over-the-counter cough medicine has been shown to reliably stop the coughing fits of pertussis. Cough suppressants do not address the underlying airway damage. This is a case where the honest answer is that symptom relief is limited.
Can Pertussis Be Prevented?
Vaccination is the most effective way to prevent pertussis. Two main vaccine types are used in the United States: DTaP for young children and Tdap for older children, adolescents, and adults. Both protect against diphtheria, tetanus, and pertussis.
Immunity from vaccination fades over time. That is why booster doses are recommended — one dose of Tdap during each pregnancy, and routine boosters for adolescents and adults as advised by a clinician. Vaccinating pregnant women protects newborns before they can be vaccinated themselves.
Vaccination does not fully prevent infection. It reduces the risk of severe illness, hospitalization, and death, particularly in infants. Vaccinated people can still catch pertussis, but the illness is usually milder and less likely to spread.
Other prevention steps include staying home while contagious, covering coughs, and washing hands often. Close contacts of a confirmed case are often offered preventive antibiotics, a practice called post-exposure prophylaxis. Whether that is appropriate depends on the person’s risk and vaccination status.
Who Is Most at Risk?
Infants under one year old face the highest risk of severe illness and death. Their airways are small, their immune systems are immature, and they may not be fully vaccinated. Apnea is a particular danger.
Other groups at higher risk include people with weakened immune systems, those with chronic lung disease, and older adults whose immunity has waned. Pregnant women are also a concern because they can pass infection to a newborn.
Adults and older children usually recover, but the cough can last for months and interfere with work, sleep, and daily life. The illness is rarely fatal in healthy adults.
Frequently Asked Questions
How long does whooping cough last?
The illness typically runs about six to ten weeks across all three stages, though a lingering cough can last longer. The cough often outlasts the infection itself because the airways take time to heal.
Is whooping cough contagious before symptoms start?
Yes, a person can spread pertussis during the early catarrhal stage, when symptoms look like a common cold. This is why outbreaks are hard to contain — people transmit the bacteria before the distinctive cough appears.
Can you get whooping cough if you were vaccinated?
Yes, vaccinated people can still catch pertussis because immunity fades over time. However, vaccination generally makes the illness milder and lowers the risk of severe complications.
When should you see a doctor for a persistent cough?
See a doctor if a cough lasts more than a few weeks, comes in severe fits, causes vomiting, or follows known exposure to someone with pertussis. Infants with any breathing difficulty or pauses in breathing need emergency care.
