Doctors Warn That The “100-Day Cough” Is Making A Dangerous Comeback

Whooping cough, also known as pertussis, is a highly contagious bacterial infection of the airways that is resurging in several countries. Often dismissed as a lingering cold, the illness can persist for months, earning the nickname “100-day cough” and posing serious risks to vulnerable individuals.

The infection is caused by the bacterium Bordetella pertussis. Research suggests that as few as 140 bacterial cells may be enough to trigger infection, which spreads through droplets released when an infected person coughs or sneezes. These droplets can infect others when they reach the nose, throat, or airways.

How The Infection Typically Progresses

Doctors generally describe pertussis in three stages. The first stage, known as the catarrhal phase, resembles a common cold, with symptoms such as a runny or blocked nose, mild cough, and low fever. Because the symptoms are nonspecific, many people do not realize they are contagious during this stage.

After one to two weeks, the illness may progress into the paroxysmal phase, which is marked by sudden and intense coughing fits. In children, these episodes may end with the characteristic gasping “whoop” sound, although adults often do not make this noise, leading to frequent missed diagnoses.

The cough can become so relentless that some people vomit or struggle to catch their breath. In adults, vomiting after coughing is considered one of the most distinctive warning signs. One study found that the average duration of coughing was 54 days, although in some cases symptoms can persist close to 100 days.

During the final convalescent phase, coughing gradually becomes less frequent and less severe. However, irritation in the airways may continue for weeks, and many people remain fatigued long after their other symptoms improve.

Why Treatment And Timing Matter

Because pertussis is caused by bacteria, antibiotics such as macrolides can be effective, especially when administered early. While antibiotics do not immediately stop the cough, they can shorten the period during which an infected person spreads the disease and may also reduce symptom severity.

A person is generally no longer considered infectious 48 hours after starting appropriate antibiotics. Without treatment, however, they may continue spreading the infection for up to 21 days after coughing begins, which is one reason delayed diagnosis contributes to community outbreaks.

Vaccination remains the most effective defense against severe disease. However, immunity gained from both childhood vaccination and previous infection gradually declines over time. As a result, adolescents and adults can become susceptible again, sometimes developing milder but still highly contagious illness.

Shifting Vaccines And Rising Cases

Pertussis tends to follow three- to five-year cycles, with waves of increased infections reported in countries including England, Australia, and the United States. In 2024, England recorded its highest number of cases in years, including several infant deaths linked to the disease.

Experts point to several contributing factors. Disruptions during the COVID-19 pandemic reduced routine childhood vaccination rates and limited natural exposure to the bacteria, leaving more people without recent immunity. At the same time, improved testing methods have made detection more accurate.

Vaccine type may also play a role. Many countries have shifted from whole-cell vaccines, which contain killed bacteria, to acellular vaccines that use selected bacterial proteins. Acellular vaccines cause fewer side effects but appear to provide shorter-lasting protection, particularly against mild infection.

As a result, vaccinated people can still contract and spread pertussis, although they are far less likely to develop life-threatening complications. Health authorities therefore continue to stress the importance of booster doses for adolescents, adults, and pregnant women.

Complications And Who Is Most At Risk

For many otherwise healthy adults, whooping cough is miserable but manageable. However, secondary complications occur in nearly 30 percent of adult cases. One of the most serious is pneumonia, which can develop when Bordetella pertussis damages the lining of the airways.

The bacterium can paralyze cilia, the tiny hair-like structures responsible for clearing mucus and germs from the lungs. Once cilia are impaired, bacteria that cause pneumonia can establish infection more easily, increasing the risk of hospitalization, especially in older adults and medically vulnerable individuals.

The physical strain caused by repeated, forceful coughing can also injure the body. Adults may develop rib fractures, particularly between the fifth and tenth ribs, while many women over 50 report urinary incontinence triggered or worsened by severe coughing episodes.

In rare cases, extreme coughing has been associated with a collapsed lung, known as pneumothorax, which occurs when lung tissue tears and air leaks into the space between the lung and chest wall. Researchers have also documented spinal fractures, disc injuries, organ herniation, and arterial tears that can lead to stroke.

People at particularly high risk include those with chronic lung disease, obesity, heart conditions, or weakened immune systems. Smokers and individuals with asthma may experience longer-lasting cough, poorer sleep, and a higher risk of sinus infections.

Confusion With RSV, Flu, And COVID

Early pertussis symptoms overlap with many respiratory illnesses, including respiratory syncytial virus (RSV), influenza, and COVID-19. This similarity means doctors may initially diagnose a more common viral infection, delaying appropriate antibiotic treatment.

One study estimated that pertussis misdiagnosis rates in adults may reach as high as 95 percent in some settings. Clinicians are encouraged to consider whooping cough when a cough lasts longer than two weeks, especially if it occurs in violent bursts or leads to vomiting.

There are also several clues that may help distinguish pertussis. The cough is often worse at night, may occur in rapid bursts with few breaths between episodes, and is not always accompanied by high fever. By comparison, RSV in adults more commonly causes wheezing and shortness of breath.

Seasonal patterns differ as well. RSV usually peaks from late autumn through early spring, particularly around December and January in the Northern Hemisphere. Pertussis, meanwhile, can circulate year-round, with outbreaks depending on vaccination rates and population immunity.

Vaccines, Boosters, And Prevention

Vaccines are available for both RSV and pertussis, although they work differently. RSV vaccines and monoclonal antibodies mainly protect against severe viral disease, while pertussis vaccines train the immune system to target bacterial toxins and reduce severe illness and transmission.

Pregnant women are considered a key group for pertussis vaccination. Receiving a booster dose during late pregnancy allows protective antibodies to cross the placenta and help shield newborns during the first weeks of life, before infants are old enough to receive their own vaccines.

Public health agencies also recommend booster doses for adolescents, adults who have not been vaccinated in many years, and close contacts of newborn babies. Healthcare workers and caregivers of infants are strongly encouraged to stay up to date with pertussis vaccination.

General preventive measures, including staying home while sick, covering coughs, frequent handwashing, and wearing masks in crowded healthcare settings, can also reduce transmission. These steps become especially important during local outbreaks or when caring for vulnerable individuals.

When To Seek Medical Advice

The main warning sign of whooping cough is a persistent cough that occurs in severe bouts, lasts for weeks, worsens at night, or causes vomiting or near-fainting. Adults should seek medical advice if these symptoms develop, especially after known exposure to someone with pertussis.

Urgent medical attention is particularly important for babies, pregnant women, older adults, and people with serious underlying health conditions. In infants, episodes involving blue lips, pauses in breathing, or difficulty feeding require emergency care because pertussis can worsen rapidly.

Doctors may confirm the diagnosis using nose or throat swabs and prescribe antibiotics to reduce infectiousness, especially among household contacts of newborns. Early recognition not only improves patient outcomes but also helps prevent further spread within the community.

With cases rising again in several regions, health authorities emphasize awareness, vaccination, and timely treatment as the most effective tools for limiting the impact of the so-called “100-day cough” on families and healthcare systems.