Pertussis, commonly called whooping cough, produces a distinctive two-part sound: a rapid-fire burst of forceful coughs followed by a high-pitched “whoop” as the person gasps for air. That whoop is the hallmark, caused by a long, strained inhalation through a narrowed airway after a coughing fit has expelled nearly all the air from the lungs. But the sound varies significantly by age, and many people with pertussis never make the whoop at all.
The Classic Coughing Fit
A pertussis coughing episode, called a paroxysm, starts with a rapid series of short, forceful coughs that come so fast the person can barely breathe between them. These aren’t single coughs spaced apart like a chest cold. They fire off in a continuous volley, sometimes 10 to 15 coughs in a row, with almost no pause to inhale. The person’s face may turn red or even bluish as oxygen runs low.
When the coughing finally pauses, the person takes a deep, desperate breath in. Because the airways are swollen and narrowed, that inhalation produces a loud, high-pitched “whoop,” almost like a squeaky gasp or a strangled intake of air. The sound is sharp enough to hear from another room. After a brief recovery of a few seconds to a minute, the cycle often starts again. These episodes can repeat dozens of times a day and tend to be worse at night.
About half of all pertussis patients vomit or gag at the end of a coughing fit. One study of Michigan cases found that post-cough vomiting occurred in roughly 49 to 54 percent of patients, depending on when they sought medical care. Between episodes, the person may seem completely fine, which is one reason pertussis often goes unrecognized early on.
How It Sounds Different by Age
The classic whoop is most recognizable in children between about 6 months and 10 years old. Their smaller airways produce the sharpest, most dramatic sound. In teens and adults, the whoop is often absent entirely. Instead, the main symptom may be a persistent, hacking cough that lingers for weeks or months, sometimes called the “100-day cough.” Adults frequently describe it as an uncontrollable coughing fit that leaves them breathless and exhausted, but without the telltale whoop that would tip someone off to pertussis.
Infants under 6 months present the most dangerous and least recognizable pattern. Very young babies may not cough forcefully enough to produce a whoop. Instead, they may have episodes of apnea, where they simply stop breathing for several seconds. Their skin may turn pale or bluish. This silent presentation is a major reason pertussis is most deadly in newborns: the infection doesn’t always sound like what parents expect.
Why the Cough Won’t Stop
The uncontrollable nature of pertussis coughing isn’t just irritation in the throat. The bacteria produce a combination of compounds that work together to hijack the body’s cough reflex. These compounds trigger the release of a molecule called bradykinin in the airways, which is a known cough inducer. Bradykinin then sensitizes nerve endings in the airway, making them dramatically more reactive to any stimulus.
What makes pertussis especially relentless is that the bacteria also block the body’s built-in mechanisms for stopping a cough once it starts. Normally, your nervous system has two separate braking systems that wind down a coughing episode after it begins. The bacterial toxin disables both of them. This is why pertussis coughing fits feel so different from a normal cough: once a paroxysm begins, there’s essentially no off switch. The coughing continues until the person is physically spent.
How It Differs From Croup
Parents sometimes confuse pertussis with croup, since both cause alarming coughs in children. The distinction is in the sound itself. Croup produces a single, harsh “barking” cough that sounds like a seal or a barking dog, caused by swelling around the vocal cords. It tends to come as individual barks rather than prolonged fits.
Pertussis sounds different: long, sustained bursts of rapid-fire coughing followed by the characteristic gasp or whoop. The coughing fits last much longer than a croup bark, often 30 seconds to over a minute, and the whoop comes at the end as the person tries to inhale. Croup also typically resolves within a week, while pertussis coughing fits persist for weeks to months.
What the Illness Looks Like Over Time
Pertussis unfolds in stages, and it doesn’t sound alarming at first. The first one to two weeks resemble an ordinary cold: mild cough, runny nose, maybe a low-grade fever. Nothing that would make you think “whooping cough.” This early phase is also when the person is most contagious, which is part of why the disease spreads so effectively.
The coughing fits with the whoop typically develop in the second or third week and can intensify over the following weeks. This paroxysmal phase usually lasts two to six weeks but can stretch longer. Gradually, the episodes become less frequent and less severe, though a residual cough can linger for months. The CDC defines a clinical case as a cough illness lasting at least two weeks with paroxysmal coughing, an inspiratory whoop, post-cough vomiting, or episodes of apnea.
Current Prevalence
Pertussis never went away, and it has been surging recently. The United States typically sees more than 10,000 cases per year, but 2024 brought a sharp spike, with more than six times as many reported cases compared to 2023. Preliminary numbers for 2025 have been trending down from a peak in November 2024, though they remain elevated compared to pre-pandemic levels. Vaccination reduced annual cases by more than 90 percent from the pre-vaccine era, when over 200,000 cases were reported each year, but immunity from the vaccine wanes over time, which is why booster shots matter for teens and adults.