Overview

Pertussis, more commonly known as whooping cough, is a highly contagious respiratory infection caused by a bacterium, Bordetella pertussis, found in the mouth, nose, and throat of infected people. The disease is infamous, not only for the “whoop” sound that comes with its severe coughing but also for its distinction from other respiratory diseases in that it can cause severe complications, particularly neurological issues. 

Severe neurological complications, such as epilepsy and encephalopathy, are the most commonly recorded neurological complications of pertussis. Although the chance of developing these complications is low, it is important to be informed about them. 

This article will guide you on the symptoms of pertussis, the neurological effects that can result from pertussis, and a deeper dive into the data on the prevalence of neurological complications.

What is pertussis?

Pertussis (whooping cough) is a highly contagious infection of the respiratory tract. It is caused by the bacterium, Bordetella pertussis. Outbreaks of pertussis were first described in the 16th century.¹

Clinical presentation and symptoms 

Pertussis is a respiratory illness characterised by repeated coughs that end with a high-pitched “whoop” sound when someone gasps for air, hence the name whooping cough.¹

In its early stages, pertussis can appear similar to a common cold. However, in contrast to a common cold, the coughing fits associated with pertussis can last for weeks  – normally between one and six weeks), but it can even last up to 10 weeks.

Early-stage symptoms

Some people may not develop symptoms of pertussis for up to three weeks after exposure to the bacteria that causes it. The following early-stage symptoms can last for between one and two weeks and may seem similar to the common cold:

• Runny or stuffy nose
• Low-grade fever (less than 38 degrees C)
• Mild and occasional coughing (this does not apply to infants)
• Apnoea (pauses in breathing that can be life-threatening) and cyanosis (turning purple or blue) among infants and young children

Later-stage symptoms

Between one to two weeks after the onset of symptoms, people with pertussis may develop paroxysms.² These are violent, rapid, and uncontrolled coughing fits, that can last for long periods as previously mentioned, and can worsen and become more common over time as the illness progresses. These coughing fits can cause patients to:

• Make the illness’s characteristic high-pitched “whoop” sound when inhaling after a coughing fit
• Vomit during or after coughing fits
• Struggle to breathe
• Become hypoxic (low oxygen levels in tissues), in severe cases

The later-stage symptoms differ between infants, teenagers and adults. Teens and adults often have much milder symptoms, especially if they have received the whooping cough vaccine. Although older patients can develop severe pertussis, the concern mainly lies with infants and young children. Many infants may not even display symptoms of pertussis (such as coughing), and it may appear similar to the common cold. Instead of the typical symptoms, pertussis can cause infants to turn blue or struggle to breathe, leading to limited oxygen supply to organs such as the brain, which can often cause severe complications. Infants with pertussis account for almost all pertussis-related hospitalisations and deaths, with the rate of major complications being 6% in infants and children, and 24% in infants that are under six months old.² These complications are either pulmonary, neurologic, or nutritional, with the pulmonary complications being the most frequent.²

Relevance

Pertussis has become a growing concern as cases have been increasing, even in countries with high vaccination rates.³ The whooping cough vaccine is normally very effective and reliable but isn’t perfect. This means there still is a possibility of becoming infected, but your symptoms will be significantly milder (i.e. a cough that doesn’t last as long and coughing fits that are less severe). 

The disease is endemic worldwide, with periodic increases of infection every two to five years.² It is highly contagious, and if someone in your household has been infected, up to 90% of household contacts will be infected. Similarly, in schools, up to 80% of classmates can potentially become infected after exposure to pertussis.²

Pertussis is of particular concern when it infects children. Although the illness can affect anyone, infants experience the highest age-specific incidence (the number of new cases in a year) of pertussis. Infants also account for the majority of hospitalisations and deaths from pertussis, with more than 80% of infected infants under two months being hospitalised.² This is often due to neurological problems arising from pertussis infection. For these reasons, in the UK, the whooping cough vaccine is routinely given to babies at 8, 12, and 16 weeks old and to children aged three years and four months of age. It is also offered to pregnant people at around 20 weeks of pregnancy to help protect the baby for the first few weeks of life. 

What are the neurological effects of pertussis?

Epilepsy

Epilepsy is a neurological disorder characterised by recurrent and unpredictable seizures. It has been known for nearly a century that epilepsy is a neurological issue that can arise from pertussis.⁴ In a study of pertussis patients in Denmark, it was found that in children at the age of 10, the chance of developing epilepsy was 1.7%. In adults, only 0.9% of pertussis patients developed epilepsy.⁵ Although children are almost twice as likely to develop epilepsy, it should be noted that the chance of that is still quite now. Another study done in Italy found that 4.1% of all pertussis patients developed some sort of neurological complication.⁷ Seizures were the common neurological problem in all these cases, however, no lasting consequences were recorded, meaning they did not have epilepsy.⁶ Epilepsy has long been recorded as a neurological problem arising from pertussis infection, and although the percentage chance of developing epilepsy or seizures is low, it is still a well-documented complication.⁴

Encephalopathy

Encephalopathy is damage to the brain that causes brain dysfunction. This brain dysfunction can appear as confusion, memory loss, or other problems leading to an altered mental state.

This disease of the brain is another well-recorded neurological complication of pertussis, as encephalitis can be quite serious, with neurological deficits following the encephalopathy.⁷

In the same study from Italy mentioned earlier, although 4.1% of patients developed neurological problems, only 0.9% of those were cases of acute encephalopathy.⁶ 

In another study, it was found that 0.4% of all infants diagnosed with pertussis will develop encephalopathy, which is one of the causes of high hospitalisation and death rates in infants with pertussis.² While the US Centers for Disease Control and Prevention reports a 0.6% chance of developing encephalopathy, it should be noted that it is one of the most uncommon side effects as seen by these percentages, and it should not be a huge concern when diagnosed with pertussis. In many cases, patients diagnosed with encephalopathy may also experience seizures or epilepsy, meaning it not always is one or the other.³

Causes and origins of neurological effects

The causes of neurological problems from pertussis are still a bit unclear, and there can be many possibilities related to the symptoms. Some causes for neurological problems can arise from anoxia (complete loss of oxygen in the body or brain) due to the paroxysmal cough, or a direct toxic effect from the pertussis toxin.² 

The most common guess for the causes of neurological is hypoxia from paroxysmal coughs, troubled breathing, or apnea as seen in the symptoms of pertussis. Low levels of oxygen reaching the brain can cause irreparable damage as it is essential for the functioning of the brain.⁴

The less popular hypothesis is the effects of the pertussis toxin, which is secreted from Bordetella pertussis, can compromise the blood-brain barrier in humans. The blood-brain barrier is a very important structure as it regulates the movement of substances in and out of the brain. However, researchers have still not been able to narrow down the cause of neurological complications from pertussis, and there is no definitive answer to this. This should not, however, be a concern though, as neurological complications from pertussis are incredibly rare with a very small chance of it ever occurring. 

Summary

Pertussis, also known as whooping cough, is a highly contagious respiratory infection caused by the bacterium, Bordetella pertussis. Although this condition is primarily known for its respiratory complications and its distinctive cough, it can also lead to neurological complications, particularly in children. These complications include epilepsy (seizures) and encephalopathy (brain damage). Despite studies on these neurological complications that have shown that the complications are incredibly rare, there is still a possibility of developing neurological problems following pertussis. Epilepsy is seen in 1.7% of patients and general seizures in 4.1% of patients. Encephalopathy was developed in 0.4-0.9% of pertussis patients in the study, which can lead to further neurological complications. 

The exact cause of these complications is still unknown to researchers, the most common hypothesis is that hypoxia (low oxygen level) from pertussis symptoms such as paroxysmal cough, difficulty breathing, or apnea. This can lead to the brain not getting enough oxygen, hence getting damaged. Another common hypothesis is the effects of the pertussis toxin secreted by the Bordetella pertussis bacteria, which is known to cause complications and can compromise the blood-brain barrier. Although this may all sound very concerning, the chances of developing neurological complications from pertussis are low, and one of the least common complications recorded. Despite the rarity of these complications, it is still recommended that babies, children, and pregnant people receive the whooping cough vaccine as part of the routine UK vaccination schedule.