The 100 day cough is another name for whooping cough, a highly contagious bacterial infection that can cause violent coughing fits lasting around three months. The name comes from the total duration of illness, which stretches roughly 100 days from the first mild symptoms through full recovery. The medical term is pertussis, caused by the bacterium Bordetella pertussis, and while most people associate it with childhood, it affects adults just as often.
Cases surged dramatically in 2024, with the CDC reporting 35,435 cases in the United States compared to 7,063 in 2023, a fivefold increase that made the infection significantly more common than it had been in recent years.
Why the Cough Lasts So Long
The bacterium behind whooping cough doesn’t just cause a simple respiratory infection. It attaches specifically to the ciliated cells lining your airways, the tiny hair-like structures responsible for sweeping mucus and debris out of your lungs. Once attached, it releases toxins that hijack the cells’ normal signaling, flooding them with a chemical messenger called cAMP. This triggers two problems at once: the cells ramp up mucus production (particularly thick, sticky mucus types known as Muc5AC and Muc5B), while the toxins also reorganize the internal scaffolding of airway cells, weakening the barrier that normally keeps pathogens out.
The result is airways clogged with excess mucus and stripped of their normal clearing mechanism. Even after the bacteria are killed off by your immune system or antibiotics, the damage to the airway lining takes weeks to repair. That’s why the cough persists long after the infection itself is gone.
The Three Stages of Illness
Whooping cough moves through three distinct phases, each with a different character.
Stage 1: The Cold Phase
The illness begins looking exactly like a common cold: runny nose, mild cough, maybe a low-grade fever. This stage typically lasts one to two weeks, and it’s easy to dismiss. The cough gradually gets worse toward the end of this phase. This is also when you’re most contagious and, critically, when antibiotics are most effective.
Stage 2: The Coughing Fits
This is the phase that gives the illness its name. The mild cough transforms into violent, uncontrollable coughing fits called paroxysms. During a fit, you cough rapidly and forcefully until virtually all the air has left your lungs, then inhale sharply, producing the characteristic high-pitched “whoop.” These fits often end with exhaustion or vomiting.
The attacks hit most frequently at night, averaging about 15 episodes per 24 hours. They increase in frequency over the first one to two weeks, plateau for two to three weeks, then gradually ease. This stage alone can last six weeks or more, making it the longest and most debilitating part of the illness.
Stage 3: Recovery
The coughing fits slowly become less frequent and less intense over another two to three weeks. Some people find that their cough lingers even beyond this, occasionally flaring up for months, particularly when triggered by other respiratory infections, cold air, or physical exertion.
How It Looks Different in Adults and Infants
Adults and older children typically experience the classic pattern described above, with violent coughing fits, the whooping sound on inhalation, and post-cough vomiting. Many adults never develop the whoop at all, which is one reason the infection goes undiagnosed so often. Instead, they may simply have a persistent, worsening cough that won’t go away for weeks.
Infants, especially those under six months, present very differently and face far greater danger. Rather than coughing fits, babies may have episodes of apnea, where they simply stop breathing. They can also turn blue from lack of oxygen. Whooping cough is most life-threatening in this age group, which is why vaccination during pregnancy is so important for passing protective antibodies to the baby before birth.
How It Spreads
Pertussis spreads through respiratory droplets when an infected person coughs, sneezes, or shares breathing space with others. A person is contagious from the very start of symptoms, before anyone suspects it’s anything more than a cold, and remains contagious for at least two weeks after coughing begins if untreated. Starting antibiotics early shortens the contagious period, which is one of the main reasons treatment matters even though antibiotics don’t dramatically reduce the cough itself once the paroxysmal stage has set in.
Getting a Diagnosis
Timing matters significantly with pertussis testing. The two main diagnostic tools have different windows of accuracy.
A nasopharyngeal culture, where a swab is inserted deep into the nose to collect a sample, is the definitive test with 100% specificity. But it needs to be collected within two weeks of cough onset, and even then its sensitivity ranges from only 30% to 60%. After three weeks, cultures rarely detect the bacteria at all.
PCR testing (a molecular test that detects bacterial DNA) is more sensitive at 94% and works within a four-week window from cough onset. In practice, many people don’t seek testing until they’ve been coughing for weeks, which narrows the options. A doctor may diagnose pertussis based on clinical symptoms alone if the testing window has passed.
Treatment and What to Expect
Antibiotics are the standard treatment, typically from a class called macrolides. For people one year and older, treatment is recommended within three weeks of cough onset. For infants under one year and pregnant women near their due date, the treatment window extends to six weeks from cough onset. Antibiotics work best when started during the cold-like first stage, before the coughing fits begin. Once the paroxysmal stage is underway, antibiotics reduce contagiousness but do relatively little to shorten the cough itself, because the damage to the airway lining has already been done.
There’s no medication that effectively suppresses the coughing fits. Over-the-counter cough medicines generally don’t help. Management at home focuses on comfort measures: eating small, frequent meals to reduce vomiting after fits, drinking plenty of fluids, using a cool mist humidifier to loosen secretions, and keeping the home free of irritants like smoke, dust, and chemical fumes that can trigger additional coughing. Staying warm and resting as much as possible helps your body direct energy toward repairing the damaged airway lining.
Physical Toll of the Coughing Fits
The force of pertussis coughing fits can cause injuries on its own. Adults commonly experience cracked or fractured ribs, hernias, pulled muscles in the chest and abdomen, and urinary incontinence during fits. Burst blood vessels in the eyes (subconjunctival hemorrhage) are also common and, while alarming in appearance, resolve on their own. The exhaustion from weeks of disrupted sleep, since fits peak at night, takes a significant toll on daily functioning, work, and mental health.
The most serious complication is pneumonia, which develops when bacteria take advantage of the damaged airways. In infants, complications also include seizures and brain damage from oxygen deprivation during apnea episodes.
Vaccination and Prevention
Whooping cough is preventable through vaccination. Children receive a series of DTaP shots in infancy and early childhood. For adults, the CDC recommends a Tdap booster, with subsequent boosters every 10 years. Vaccine-induced immunity fades over time, which is one reason outbreaks still occur even in well-vaccinated populations. Many adults are unknowingly unprotected because they haven’t had a booster in over a decade.
Pregnant women are advised to get a Tdap booster during each pregnancy, ideally during the third trimester, so that protective antibodies cross the placenta and give the newborn some immunity during the vulnerable first months before the baby can be vaccinated. Given the sharp rise in cases in 2024, checking your booster status is a practical step, particularly if you spend time around infants or work in settings with close physical contact.