Introduction

Understanding the unique characteristics and symptoms of pertussis, also known as whooping cough, is essential for distinguishing it from other similar respiratory illnesses with similar symptoms. With its severe and violent coughing fits and “whoop” sound that comes following the coughing fits, pertussis can easily be distinguished from other respiratory illnesses. Certain symptoms are strongly associated with pertussis as well, including apnea, cyanosis, or hypoxia from the unique severe coughs. This article will provide in-depth information about what pertussis is, including symptoms and complications of it as well as of the most similar respiratory illnesses, showing what to look out for and how to differentiate pertussis. 

What is Pertussis?

Pertussis, commonly known as whooping cough, is a unique and acute infectious disease that is highly contagious. It is caused by the bacteria Bordetella pertussis, and it has been around since the 16th century.¹

Clinical presentation and symptoms

Pertussis is a coughing illness that can last for an extended period of time, normally 1 to 6 weeks, but it can even last up to 10 weeks.² It is characterized by its repeated coughs that end with a high-pitched “whoop” sound, hence the name whooping cough.¹

Pertussis may begin similarly to a common cold, but in contrast to a cold, the coughing will last for up to weeks or months. Sometimes, you may not even develop symptoms of pertussis for up to 3 weeks.

Early Stage Symptoms

These symptoms can last for 1 to 2 weeks, and may seem similar to the common cold.² These include:

• Runny or stuffy nose
• Low-grade fever (less than 38⁰C)
• Mild and occasional coughing (this does not apply to infants)
• Apnea (pauses in breathing that can be life-threatening), and cyanosis (turning purple or blue), seen in infants and young children

Later stage Symptoms

Following those 1 to 2 weeks from when symptoms have started, patients with pertussis can develop paroxysms. These are violent, rapid, and uncontrolled coughing fits can last for long periods as previously mentioned, and can worsen and become more common over time as the illness progresses.² These coughing fits can make patients:

• Make the typical high-pitched “whoop” sound when inhaling again after a coughing fit
• Vomit during or after coughing fits
• Struggling to breathe
• Hypoxia (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 been vaccinated against it. Although older patients can develop severe pertussis, the problem mainly lies with infants and young children.

Many infants may not even display symptoms of pertussis such as coughing, and it may just be seen as the common cold. Instead, it can cause infants to turn blue or struggle to breathe, leading to limited access to oxygen for tissues such as the brain, which can often have very severe complications.²

Infants with pertussis account for almost all hospitalization and death cases from pertussis, with the rate of major complications being 6% in infants and children, and 24% in infants that are under 6 months old.³ These complications are often neurologic, pulmonary, or nutritional.

Relevance

Pertussis is becoming more and more relevant and is a growing concern as pertussis is re-emerging, even in countries with high vaccination rates.⁴ Although the pertussis vaccines are normally very effective and reliable, they aren’t perfect.² This means there still is a possibility of getting infected, but your symptoms will be significantly milder, which is why the US Centers for Disease Control and Prevention recommends the vaccine for all ages.²

This disease is endemic worldwide, with periodic increases of infection every 2-5 years.³ It is quite 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 possibly be infected after exposure to pertussis.³

Pertussis particularly becomes relevant when it infects children. Although it can affect anyone, it is infants’ age group who have the highest number of age-specific incidents following pertussis. They account for the majority of hospitalisations and deaths from pertussis, with more than 80% of infected infants under 2 months being hospitalised.³ This is often due to neurological problems arising from pertussis infection.

Common Respiratory Illnesses With Similar Symptoms

Early stage symptoms of pertussis can easily be mistaken for any common illness. The symptoms of pertussis within the first 1 or 2 weeks are quite mild, and can be mistaken for any common cold or flu going around, and it would be very hard to diagnose pertussis based on these symptoms.

A study done on pertussis-like syndrome found that influenza, respiratory syncytial virus, and pneumonia were the most common illnesses confused for pertussis.⁵

Influenza

Influenza, commonly known as flu, is a widespread and acute respiratory illness caused by influenza viruses. Symptoms of influenza include dry coughing, fever, headaches, muscle and joint pain, runny nose, and sore throat. The cough can be severe and it can last up to 2 weeks or more, and it can lead to pneumonia in severe cases. Similarly to pertussis, it is a leading cause of death in children, and the symptoms of it are very similar to early-stage symptoms of pertussis.⁶

Respiratory Syncytial Virus (RSV)

Respiratory syncytial virus (RSV) is a common respiratory illness. It causes mild flu-like symptoms such as coughing, sneezing, fever, wheezing, runny nose, and a decrease in appetite. Most people usually recover quite quickly from RSV, within 1-2 weeks, but in more severe cases it can lead to bronchitis or pneumonia.⁷

Pneumonia

Pneumonia is the inflammation of the lungs caused by either a bacteria, virus, or fungi. Symptoms may include coughing, shortness of breath, chest pain, body aches, loss of appetite, feeling tired, and wheezing noises when the patient breathes. The complications of severe pneumonia can be serious, with patients experiencing difficulty breathing and requiring a ventilator, fluid accumulation in the lungs, or lung abscesses.⁸

Parapertussis

Parapertussis is a less common respiratory illness caused by the bacteria Bordetella parapertussis. Although it can be very similar to pertussis, especially considering they are in the same genus Bordetella, parapertussis is much less severe than pertussis. The two illnesses have almost the exact same symptoms; however, the symptoms present themselves as much milder in parapertussis, and they clear up relatively fast compared to pertussis. The milder symptoms of parapertussis also means that there is a very small chance of developing symptoms such as apnea, cyanosis, or hypoxia.⁹

What Sets Pertussis Apart?

Although all these similar symptoms may cause confusion about what illness you may have, it can be easy to narrow it down to pertussis as certain signs set pertussis apart from other pertussis-like respiratory illnesses.

Unique Symptoms

• Paroxysmal cough: Although almost all respiratory illnesses come with a cough, the cough from pertussis is quite severe. Paroxysmal coughs are violent, rapid, and uncontrolled coughing fits that can last for long periods.² These coughs can cause difficulties in breathing and the body receiving enough oxygen, which leads to the symptoms earlier mentioned such as hypoxia, apnea, or cyanosis.
• Whooping sound: The “whoop” sound that comes with pertussis cough is a hallmark of pertussis, giving it its name whooping cough. After a violent and long coughing spell, all the air has left the lungs and the patient is forced to inhale. When the patient inhales, they make a high-pitched “whoop” sound.¹⁰
• Apnea, Cyanosis, and Hypoxia: Although these can again result from other respiratory illnesses, they are quite strongly associated with pertussis due to the severe coughing fits.² The prolonged coughing obstructs breathing, leading to these symptoms.

Duration of Illness

Pertussis is also known as the 100-day cough, due to how long it takes to recover from it.¹¹ The similar respiratory illnesses can have severe coughing, but they usually resolve within a much shorter time frame compared to pertussis. In extreme cases, it can last up to 10 weeks which is quite uncommon for the pertussis-like illnesses mentioned.²

Complications

Due to the severe coughs, pertussis can have much more severe complications compared to other pertussis-like illnesses. The violent coughing can lead to respiratory complications such as pneumonia, while the hypoxia from the lack of oxygen can lead to neurological complications such as seizures or encephalopathy in severe cases.¹² Although many respiratory illnesses share pneumonia as a common complication, the hypoxia leading to severe complications is what sets pertussis apart from other respiratory illnesses. 

Summary

Pertussis is a highly contagious respiratory illness caused by the bacteria Bordetella pertussis. Many of its symptoms can easily be mistaken for other respiratory illnesses such as RSV, influenza, pneumonia, or parapertussis, particularly during the early-stage symptoms of pertussis, with common symptoms such as a runny nose, mild cough, and fever. However with the later stage symptoms, pertussis is truly a very unique respiratory illness with its severe and violent paroxysmal coughs that can last up to 10 weeks, and the unique “whoop” sound that comes from inhaling after a severe coughing fit, it is easy to tell apart pertussis from other respiratory illnesses. 

Due to the severe coughing fits that are associated with pertussis, apnea and cyanosis are common symptoms as well as hypoxia, which can lead to complications that are rather unique for a respiratory illness. The severe and extended coughing symptoms of pertussis, along with the problems it causes for breathing due to the coughing, set it apart from other respiratory illnesses and make it easily distinguishable.