Pertussis, commonly known as whooping cough, is a highly contagious respiratory illness that can affect people of all ages, though it poses the greatest danger to infants and young children. The disease begins with symptoms that resemble a common cold but progresses to severe coughing fits that can last for weeks or even months, earning it the nickname “the cough of 100 days.”

What Is Pertussis

Pertussis is a respiratory infection caused by a type of bacteria called Bordetella pertussis. This bacterium is found only in humans, making people both the source and the victim of this disease. The bacteria work by attaching themselves to tiny, hair-like extensions called cilia that line parts of the upper respiratory system. Once attached, these bacteria release harmful substances known as toxins, which damage the cilia and cause the airways to swell.^[1]

The name “whooping cough” comes from the distinctive high-pitched sound that many people make when they try to breathe in after a coughing fit. This whooping noise is particularly common in children and happens because the airways become so irritated and swollen that catching a breath becomes difficult. However, not everyone with pertussis makes this sound, especially teenagers and adults, who may only experience a persistent hacking cough.^[2]

Before vaccines became available in the 1940s, pertussis was a major cause of illness and death in infants. The disease was first described during an outbreak in Paris in 1578, and the bacterium responsible was discovered in 1906. Thanks to widespread vaccination programs, the number of cases dropped dramatically in the decades following the introduction of the vaccine. However, in recent years, pertussis cases have been rising again in many parts of the world.^[5]

Epidemiology

Pertussis remains a significant public health concern around the world. Globally, there are more than 24 million cases of pertussis each year, with over 160,000 deaths reported annually. In 2018 alone, the World Health Organization documented more than 151,000 cases worldwide. The disease affects populations in both low-income and high-income countries, though the burden of severe disease and death is heaviest in regions with limited access to healthcare and vaccines.^[5][6]

In the United States, the number of pertussis cases has fluctuated significantly over the decades. After reaching a historic low of just 1,010 reported cases in 1976, cases have been climbing steadily. The country experienced a peak of 48,277 cases in 2012, and in 2018, there were 15,609 reported cases. More recent data shows that pertussis activity has increased throughout the United States, with over 11,000 cases reported as of August 2024, compared to only 3,021 cases in the entire year of 2023. Some states have seen particularly dramatic increases, with Pennsylvania reporting 1,666 cases in 2024 compared to just 179 cases in 2023.^[5][15]

The increase in pertussis cases is partially attributed to waning immunity among adolescents and adults. Protection from the vaccine fades over time, leaving previously vaccinated individuals vulnerable to infection. Additionally, although pertussis largely remains a disease that primarily affects children, with 38 percent of cases occurring in infants younger than six months and 71 percent in children younger than five years, adolescents and adults are increasingly contracting the disease and likely contributing to the spread to vulnerable populations.^[5]

Causes

The sole cause of pertussis is infection with the bacterium Bordetella pertussis. Less commonly, a related bacterium called Bordetella parapertussis can cause similar symptoms, though usually milder. In rare cases, immunocompromised individuals may contract Bordetella bronchiseptica, which typically affects animals and is known as “kennel cough.”^[5]

Humans are the only reservoir for Bordetella pertussis, meaning the bacteria cannot survive in animals or the environment for long periods. The bacteria spread from person to person through the air when an infected individual coughs or sneezes. These actions release tiny droplets containing the bacteria into the air, which other people can then breathe in. The bacteria can also sometimes spread when someone touches a surface contaminated with respiratory secretions and then touches their nose or mouth.^[4]

Pertussis is extremely contagious. The bacteria spread easily when people spend significant time together or share breathing space, such as in households, classrooms, or childcare settings. Studies show that pertussis often affects 100 percent of non-immune household contacts. If someone with pertussis is in close proximity to others, the likelihood of transmission is very high. This is particularly concerning because many people with pertussis don’t know they have it, especially in the early stages when symptoms resemble a common cold.^[5]

People with pertussis are most contagious during the first two weeks after coughing begins, though they can spread the bacteria from the very start of symptoms. This means someone can be spreading the disease before they even realize they’re sick. Taking antibiotics early in the illness can shorten the period during which someone is contagious, but without treatment, people can continue spreading the bacteria for at least two weeks after the cough starts. Many babies who get whooping cough are infected by older siblings, parents, or caregivers who have mild symptoms and don’t realize they’re carrying the disease.^[1]

Risk Factors

Certain groups of people face higher risks when it comes to pertussis. Age is one of the most important risk factors. Babies younger than one year old are at the greatest risk for getting whooping cough and developing severe complications from it. This is especially true for infants under six months of age, who may not have received enough vaccine doses to be fully protected. More than half of babies under one year old who get whooping cough require hospitalization because the infection can cause them to stop breathing.^[1][8]

Pregnant women in their third trimester represent another high-risk group, not because they’re more likely to develop severe disease themselves, but because they may transmit the infection to their newborn infant. Since newborns cannot be vaccinated until they’re at least six weeks old, they depend entirely on immunity passed from their mother and on the people around them being free from infection.^[1]

People with certain pre-existing health conditions are also at higher risk of developing severe pertussis infections. Those with immunocompromising conditions, which are diseases or treatments that weaken the immune system, may struggle to fight off the infection. People with moderate to severe medically treated asthma may experience worsening of their respiratory symptoms if they contract pertussis. Other underlying pulmonary, cardiac, or neuromuscular diseases can also increase the risk of complications.^[1][5]

Lack of immunization is a major risk factor for acquiring pertussis. People who have never been vaccinated or who haven’t received all recommended vaccine doses are far more vulnerable to infection. Additionally, because immunity from both vaccination and natural infection wanes over time, adolescents and adults whose protection has faded are at increased risk. Immunity can decrease to 50 percent just 12 years after completing a vaccination series.^[5]

Close contact with an infected individual is another significant risk factor. People who share confined spaces with someone who has pertussis, especially for more than an hour, are at high risk of catching the disease. This includes household members, classmates, coworkers, and healthcare providers. Exposure during epidemic outbreaks also increases the risk of infection.^[5]

Symptoms

The symptoms of pertussis vary based on a person’s age and whether they’ve been vaccinated. The disease typically progresses through three distinct stages, each with different characteristics. Understanding these stages can help people recognize pertussis and seek appropriate medical care.^[2]

Once someone becomes infected with pertussis, it usually takes about five to 10 days for symptoms to appear, though sometimes it can take up to three weeks. This period is called the incubation period. The disease then unfolds in stages that can last for many weeks or even months.^[2]

Stage One: The Catarrhal Stage

The first stage lasts about one to two weeks and is called the catarrhal stage. During this time, symptoms are mild and often indistinguishable from a common cold. People may experience a runny or stuffy nose, red and watery eyes, a mild fever or normal temperature, and a mild or occasional cough that gradually gets worse. Some people feel generally unwell or “off,” a feeling doctors call malaise. Unfortunately, this is when people are most contagious, even though they usually don’t realize they have anything more serious than a cold.^[2]

Stage Two: The Paroxysmal Stage

The second stage typically lasts anywhere from one to six weeks, though it can sometimes continue for up to 10 weeks. This is called the paroxysmal stage, named after the severe coughing fits, or paroxysms, that characterize it. During this stage, thick mucus builds up inside the airways, causing rapid, uncontrollable coughing that can’t be stopped. The cough can last for weeks or months and often gets worse at night.^[2]

These intense coughing attacks can be frightening and exhausting. People may cough so many times in a row that they struggle to catch their breath. When they finally do manage to breathe in, they may make a high-pitched “whoop” sound. However, not everyone makes this sound, particularly teenagers and adults with mild illness, who may only have an ongoing hacking cough. The coughing fits can become so violent that they cause vomiting, leaving the person exhausted afterward. Some people’s faces turn red or blue during coughing fits due to the effort and lack of oxygen. Activities like crying, eating, or laughing may trigger these episodes.^[2]

Babies often have different symptoms during this stage. Many infants with pertussis don’t cough at all. Instead, they may gag or struggle to breathe. Some babies experience life-threatening pauses in breathing called apnea. Their skin, lips, or nails may turn blue or purple from lack of oxygen, a condition called cyanosis. This is a medical emergency requiring immediate care.^[2]

Stage Three: The Convalescent Stage

The third and final stage can last up to six weeks and is called the convalescent stage, or recovery stage. During this time, the cough gradually becomes milder and happens less often. However, recovery is slow, and people may still have a mild cough that comes and goes. Even months after the initial infection, the coughing fits can return if the person gets another respiratory infection, as the airways are still healing and remain sensitive.^[2]

Prevention

The best way to prevent pertussis is through vaccination. Vaccines protect individuals from getting sick and help prevent the spread of disease in communities. The Centers for Disease Control and Prevention recommends pertussis vaccination for people of all ages.^[1]

Vaccination Schedule

There are two vaccines used in the United States to protect against pertussis: DTaP for infants and children, and Tdap for preteens, teens, and adults. Both vaccines also provide protection against tetanus and diphtheria.^[4]

Infants and young children receive the DTaP vaccine in a series of doses. The schedule includes four doses given at two months, four months, six months, and between 15 and 18 months of age. A booster dose is recommended at four to six years of age. The World Health Organization recommends the first dose be given as early as six weeks of age, with subsequent doses given four to eight weeks apart. A booster dose is recommended during the second year of life.^[6][8]

Preteens should receive a dose of Tdap at 11 to 12 years of age. Adults who have not had Tdap should get one dose to protect themselves, followed by a Tdap or Td booster every 10 years. For convenience, Tdap may replace any dose of Td vaccine that is otherwise due.^[4][8]

Vaccination During Pregnancy

One of the most important prevention strategies is vaccinating pregnant women. All pregnant individuals should receive a dose of Tdap between 27 and 36 weeks of pregnancy, during the third trimester, with each pregnancy. This allows the mother’s immune system to produce antibodies that pass to the baby before birth, providing the newborn with crucial protection during the first few months of life when they’re most vulnerable and haven’t yet received their own vaccines. This strategy has proven effective in preventing disease in infants too young to be vaccinated themselves.^[2][6][8]

Preventive Antibiotics

In addition to vaccination, preventive antibiotics, also known as postexposure antimicrobial prophylaxis or PEP, play a role in preventing pertussis. These are medicines given to someone who has been exposed to the bacteria to help prevent them from getting sick. Healthcare providers or health departments generally decide who should receive preventive antibiotics based on several factors.^[1]

Preventive antibiotics are recommended for household contacts of someone with pertussis and for people exposed to pertussis who are at high risk of severe illness, such as infants under 12 months, pregnant women in their third trimester, and people with immunocompromising conditions. They’re also recommended for people who have close contact with someone at high risk. If you’ve been exposed to someone with whooping cough, it’s important to talk to a healthcare provider about whether you should receive preventive antibiotics.^[1]

Good Hygiene Practices

Practicing good hygiene can help prevent the spread of pertussis and other respiratory illnesses. This includes covering coughs and sneezes with a tissue or the inside of your elbow, washing hands frequently with soap and water, avoiding touching your face with unwashed hands, and staying home when sick to avoid spreading germs to others.^[1]

Isolation Measures

Babies and other people at high risk of serious disease should be kept away from people who have whooping cough. For hospitalized patients, in addition to standard precautions, droplet precautions are recommended for five days after starting effective antibiotic therapy or until three weeks after the onset of coughing fits if antibiotics are not given.^[1]

Immunity After Infection

People who’ve had whooping cough develop some immunity to future infections. However, getting sick with whooping cough doesn’t provide lifelong protection. Both natural infection and vaccination offer protection that fades over time, which is why booster doses are important throughout life.^[1]

Pathophysiology

Understanding what happens in the body during a pertussis infection helps explain why the symptoms are so severe and long-lasting. The disease process involves complex interactions between the bacteria and the body’s respiratory system.^[1]

When Bordetella pertussis bacteria enter the respiratory tract through inhaled droplets, they specifically target and attach to the cilia. These are tiny, hair-like structures that line the upper respiratory system, including the trachea and bronchi. In healthy individuals, cilia work continuously in coordinated waves to move mucus and trapped particles up and out of the airways, helping to keep the lungs clean and clear.^[1]

Once attached, the bacteria begin producing several types of toxins. These harmful substances have multiple effects on the respiratory system. They damage and paralyze the cilia, preventing them from performing their normal cleaning function. As a result, mucus accumulates in the airways instead of being cleared out. The toxins also cause inflammation, leading to swelling of the airways. The combination of accumulated thick mucus and inflamed, narrowed airways triggers the body’s cough reflex in an attempt to clear the obstruction.^[1]

The coughing fits characteristic of pertussis are an extreme manifestation of this reflex. Because the airways are so irritated and obstructed, the cough becomes violent and repetitive. The mucus is thick and difficult to dislodge, leading to prolonged coughing episodes. Between coughs, the narrowed and inflamed airways make it difficult to breathe in, which can produce the characteristic whooping sound as air is forcefully drawn through the constricted passages.^[2]

The damage to the cilia and airways isn’t immediately reversible. Even after the bacteria are eliminated from the body, either naturally or with antibiotics, the airways remain damaged and inflamed. This explains why the cough persists for weeks or months after infection. The respiratory system needs time to heal, repair the damaged cilia, and restore normal function. During this healing period, the airways remain sensitive and prone to coughing, especially if exposed to other respiratory irritants or infections.^[10]

In severe cases, particularly in infants, the infection can cause additional complications. The thick mucus and severe coughing can lead to pneumonia when bacteria or other pathogens invade the damaged lungs. The violent coughing and lack of oxygen during coughing fits can cause seizures or other neurological problems. In the most severe cases, infants may experience apnea, where breathing stops entirely, potentially leading to brain damage or death if not quickly addressed.^[5]

The body’s immune response also plays a role in the disease process. White blood cells, particularly lymphocytes, increase dramatically in response to the infection, a condition called lymphocytosis. While this represents the body’s attempt to fight off the bacteria, it can also contribute to complications in some cases.^[5]