Pertussis

Pertussis, commonly called whooping cough, is a highly contagious respiratory infection that can cause severe coughing fits lasting for weeks or even months. While it affects people of all ages, it poses the greatest danger to babies, who may experience life-threatening complications.

Table of contents

• What is pertussis?
• Other names for this disease
• What causes pertussis?
• Symptoms and stages
• Who is at risk?
• How pertussis spreads
• Diagnosis
• Treatment
• Prevention
• Global impact

What is pertussis?

Pertussis is a respiratory illness caused by a type of bacteria. The disease is only found in humans^[1]. Many people with this illness develop a serious hacking cough. When someone tries to breathe in after coughing, they may make a high-pitched noise that sounds like a “whoop,” which is how the disease got its common name^[2].

The cough can become so severe that it results in vomiting and extreme tiredness. In some cases, people may cough so violently that they break ribs^[2]. The coughing fits can last for weeks or even months, which is why pertussis is sometimes called “the cough of 100 days”^[5].

Whooping cough, the cough of 100 days

Other names for this disease

This condition is most commonly known as whooping cough because of the distinctive whooping sound many people make when gasping for air after a coughing fit. It has also been called the cough of 100 days because symptoms can persist for such a long time^[5].

What causes pertussis?

Pertussis is caused by bacteria called Bordetella pertussis. These bacteria were discovered in 1906^[5]. When the bacteria enter the body, they attach to tiny, hair-like extensions called cilia that line part of the upper breathing system. The bacteria then release poisons called toxins, which damage the cilia and cause the airways to swell^[1].

In rare cases, other related bacteria can cause similar illnesses. Bordetella parapertussis can cause a milder form of the disease, and Bordetella bronchiseptica, which typically affects animals, can sometimes infect people whose immune systems are weakened^[5].

Humans are the only reservoir for these bacteria, meaning they don’t naturally live in animals or the environment^[5].

Symptoms and stages

Pertussis develops in three distinct stages, and symptoms can vary based on a person’s age and whether they have been vaccinated^[1][2].

Once someone becomes infected with pertussis, it typically takes about 5 to 10 days for symptoms to start, though sometimes it can take up to three weeks^[2][4].

Stage 1: Early symptoms (1 to 2 weeks)

The first stage is often called the catarrhal stage. During this time, the symptoms are mild and may seem like a common cold. People are most contagious during this stage, but they might not realize they have pertussis^[1].

Symptoms during this stage include:

• Runny or stuffy nose
• Red, watery eyes
• Mild fever (usually under 100.4 degrees Fahrenheit)
• Sore throat
• Mild, occasional cough that gradually gets worse
• Feeling generally unwell^[2][4]

Stage 2: Severe coughing fits (1 to 6 weeks or longer)

The second stage is called the paroxysmal stage. This is when the most recognizable symptoms appear. Thick mucus builds up inside the airways, causing rapid coughing that cannot be controlled^[2].

During this stage, people experience:

• Many rapid coughs in a row (coughing fits or paroxysms)
• A high-pitched “whoop” sound when trying to breathe in after coughing
• Vomiting during or after coughing fits
• A red or blue face during coughing episodes
• Extreme tiredness after coughing fits

The coughing fits may be worse at night and can be triggered by crying, eating, or laughing. People with mild cases or those who have been vaccinated may not make the whooping sound. Sometimes, an ongoing hacking cough is the only symptom in teenagers and adults^[2].

Stage 3: Recovery (up to several weeks)

The final stage is the convalescent stage. During this time, the cough gradually becomes milder and happens less often. However, even as symptoms improve, people remain vulnerable to other respiratory infections. If they catch another illness during recovery, the severe coughing fits may return^[1].

Special concerns for babies

Many babies with pertussis don’t cough at all. Instead, they may struggle to breathe, gag, or have pauses in breathing called apnea. Their skin, lips, or nails may turn blue or purple from lack of oxygen. These are signs that require immediate medical attention^[2][4].

Who is at risk?

Pertussis can affect anyone, but certain groups face higher risks of severe disease and complications^[1].

Age-related risks

Babies younger than one year old are at the greatest risk for getting pertussis and having severe complications. This group accounts for 38% of all cases. Overall, 71% of cases occur in children younger than 5 years^[5].

Although pertussis largely remains a disease affecting children, teenagers and adults can also contract it. Many babies get infected by older siblings, parents, or caregivers who don’t know they have the disease because their symptoms are mild^[1].

About half of babies under age one who get whooping cough need care in a hospital. Deaths linked with pertussis are rare but most often occur in infants^[2][4].

Medical conditions

People with pre-existing health conditions that may be worsened by pertussis are at high risk for developing severe infection. Some conditions that could be made worse include:

• Conditions that weaken the immune system (immunocompromising conditions)
• Moderate to severe medically treated asthma^[1]

Pregnancy

Women in their third trimester of pregnancy are considered at high risk. Severe and sometimes fatal pertussis-related complications occur in infants, and pregnant women may become a source of infection for their newborn baby^[5].

How pertussis spreads

Pertussis is very contagious and spreads easily from person to person through the air^[1]. The bacteria are spread through tiny droplets when an infected person coughs, sneezes, or breathes very close to someone. Other people can then breathe in these bacteria^[4].

The bacteria can spread when people spend a lot of time together or share breathing space. Pertussis is so contagious that it often affects 100% of non-immune household contacts. In fact, 8 out of 10 non-immune people will be infected when exposed to someone with the disease^[1][15].

How long people remain contagious

People can spread the bacteria from the start of symptoms and for at least 2 weeks after coughing begins. If treated with antibiotics early in the illness, the contagious period may be shortened to about 5 days after starting treatment^[1][4].

Silent spread

Some people have mild symptoms and don’t know they have pertussis, but they can still spread the bacteria to others. This makes the disease particularly dangerous, as infected people may unknowingly pass it to vulnerable individuals like babies^[1].

Diagnosis

Healthcare providers use several tools to diagnose pertussis^[4]:

• Medical history: The provider will ask about symptoms and possible exposure to pertussis
• Physical examination: A complete examination helps assess the severity of illness
• Laboratory tests: The most common test involves taking a sample of mucus from the back of the throat through the nose. This can be done with a swab or a syringe filled with saline. The sample is then tested for the bacteria that cause pertussis using a test called polymerase chain reaction (PCR)^[4]

PCR testing has replaced culture as the preferred method for confirming pertussis diagnosis^[5]. Other tests that may be used include blood tests to check for certain changes and chest X-rays if complications are suspected^[4].

Healthcare providers should strongly consider testing and treating before results come back if the person is at high risk for severe disease or has contact with someone at high risk^[11].

Treatment

The treatment for pertussis focuses on two main goals: using antibiotics to stop the spread of infection and managing symptoms at home^[10].

Antibiotic treatment

Healthcare providers generally treat pertussis with antibiotics. It’s very important to treat the disease early, before severe coughing fits begin. Early treatment can make the illness less serious and help prevent spreading the bacteria to others^[10].

The preferred antibiotic for treatment is azithromycin. Other antibiotics that may be used include clarithromycin, erythromycin, and trimethoprim-sulfamethoxazole^[11].

Starting treatment after three weeks of illness is unlikely to help, even though most people still have symptoms. By then, the bacteria are gone from the body. The ongoing symptoms occur because the airways were damaged and need time to fully heal^[10].

Hospital care

Pertussis can sometimes be very serious and require treatment in a hospital, especially for babies. Hospital treatment usually focuses on:

• Keeping breathing passages clear
• Monitoring breathing and giving oxygen if needed
• Preventing or treating dehydration through fluids given through a vein
• Managing complications^[10]

Managing symptoms at home

Most people with pertussis can manage their symptoms at home. Healthcare providers recommend:

• Taking antibiotics exactly as prescribed
• Keeping the home free from things that cause coughing, such as smoke, dust, and chemical fumes
• Using a clean, cool mist humidifier to loosen mucus and soothe the cough
• Eating small meals every few hours to help prevent vomiting
• Drinking plenty of fluids, including water, juices, and eating fruits
• Getting plenty of rest^[10]

Cough medicine probably won’t help and is not usually recommended, especially for children younger than 4 years old^[10].

There is limited evidence that treatments specifically aimed at reducing the severity of the cough are effective. While various treatments have been proposed, including corticosteroids and other medications, studies have not shown clear benefits^[13].

Preventive antibiotics

Some people should receive antibiotics to prevent them from getting sick if they have been around someone with pertussis. These are called postexposure antimicrobial prophylaxis (PEP)^[1].

Preventive antibiotics are recommended for:

• Household contacts of someone with pertussis
• People exposed to pertussis who are at high risk of severe illness, such as infants, people with weakened immune systems, or those in the third trimester of pregnancy
• People who are in close contact with someone at high risk^[1][14]

Azithromycin is the preferred antibiotic for prevention as well^[11].

Prevention

Vaccination

The best way to prevent pertussis is to get vaccinated. A vaccine was first developed in the 1940s^[5]. Before the pertussis vaccine was developed, pertussis was a major cause of infant illness and death^[5].

There are two vaccines available that protect against pertussis:

DTaP vaccine is given to infants and children. The vaccine also protects against diphtheria and tetanus. The schedule includes doses at 2, 4, 6, and 15-18 months of age, with a booster dose at 4-6 years^[8].

Tdap vaccine is given to adolescents and adults. It is recommended at 11-12 years of age. Adults who have not had Tdap should get one dose to protect themselves, then a booster every 10 years^[8].

Vaccination during pregnancy

All pregnant people should receive Tdap between 27 and 36 weeks of pregnancy (during the third trimester) with each pregnancy. This vaccination helps protect newborn babies by allowing the mother’s immune system to give pertussis immunity to the infant. Vaccinating pregnant women is effective in preventing disease in infants too young to be vaccinated themselves^[2][6].

Vaccine effectiveness and waning immunity

While the pertussis vaccine is effective, protection against the disease fades over time. Immunity can wane to 50% twelve years after completing a vaccination series^[5]. This waning immunity is one reason for the recent increase in pertussis cases^[15].

Other prevention measures

Good hygiene practices help prevent the spread of bacteria and viruses that cause respiratory illnesses. Babies and other people at high risk for serious disease should be kept away from people who have pertussis^[1][4].

Re-infection

People who have had pertussis have some immunity to future infections. However, getting sick with pertussis doesn’t provide complete, lifelong protection. You can get pertussis more than once^[1][15].

Global impact

Pertussis remains a significant public health concern worldwide. In 2018, there were more than 151,000 reported cases of pertussis globally^[6]. However, the actual number is likely much higher. Worldwide, there are over 24 million cases annually, with more than 160,000 deaths^[5].

Pertussis remains one of the leading causes of vaccine-preventable deaths worldwide^[3]. The disease exists worldwide, and international travelers should be up to date with this routine vaccine^[8].

In the United States, reported pertussis cases have been increasing. The number of cases decreased dramatically after universal childhood immunization was introduced, from 150,000 to 250,000 cases per year in the time before vaccines to a low of 1,010 cases in 1976. Since then, cases have risen steadily, partially due to waning immunity in adolescents and adults. In 2012, there were 48,277 reported cases. The most recent data from 2018 showed 15,609 reported cases^[5].

In 2024, pertussis activity has increased throughout the United States. There have been more than 11,000 cases in the U.S. as of August 2024, compared with a total of 3,021 cases in the entirety of 2023^[15].

Due to the difficulty in diagnosis, actual numbers are likely underreported. Many cases go unrecognized, especially in adolescents and adults who may have milder symptoms^[5].