Pertussis – everything you need to know about whooping cough

What is pertussis?

Pertussis is an infectious disease caused by the bacteria Bordetella pertussis – and it causes a characteristic cough called “whooping cough”. It also used to be called the “100-day-cough” because it can last for weeks to months, as you will see below.
It is a dangerous and infectious disease, especially for young infants, but also for the elderly.

Is pertussis a common disease?

Between 2004 and 2006, the morbidity rate of pertussis increased 14-fold compared to the years 1996-1998. And the rate is still on the rise today. This rise in mortality is evident in all age groups but especially in children under the age of 1 year and those between ages 5-14 years.

Why is the prevalence of pertussis increasing?

Whooping cough is an infection that spreads only in humans, and it is very contagious. Practically speaking, almost every single person who will be in close contact with an infected person and isn’t properly vaccinated will catch it.
Pertussis bacteria spreads through droplets that were produced during coughing or sneezing. Exposure to these in the environment or through direct contact with secretions can cause infection.
Unfortunately, those that have had the infection in the past are not protected from the disease. That means that getting the actual disease does not produce sufficiently effective immunity. Additionally, those vaccinated are also not always protected from getting the infection because of the vaccine’s weaning immunity – read more about this below.
In practice, the source of transmission is mainly older siblings and adults that catch the disease and start coughing. Those infected usually suffer from severe coughing episodes that may last for a very long time (more about this below). Usually, they do not present with fever either so most people do not visit the doctor and just wait for their disease to resolve spontaneously. During this time, they often go around spreading this bacteria (unknowingly), and that is how younger children catch it too. Then these younger children transmit the infection back to older adults. And the cycle repeats.
On average, the incubation period is around 10 days (can be anywhere between 5 days to 3 weeks).

What are the signs and symptoms of pertussis?

The disease has three characteristic stages and they are relatively long-lasting (remember the name 100-day-cough):
Catarrhal stage – or in other words, the snot stage.
Pertussis starts with a stage that is quite similar to other upper respiratory tract viral infections, with typical signs including a runny nose and cough. At this stage, it is difficult to tell that a person has pertussis as there is nothing special about this stage that differentiates it from other viral infections. This is the most contagious stage, and it lasts for about 3 weeks following the presentation of symptoms. This stage just gets worse and worse and slowly turns into the second stage of the disease, when the characteristic cough becomes more prominent.
Paroxysmal stage – or in other words, the coughing-spells or fits stage.
This is the stage during which the characteristic clinical symptoms of pertussis, which cause the physician to suspect the infection, present. In pertussis, the cough presents with long coughing fits – a series of short coughs followed by a whooping sound when the person breathes in, that is why the infection is referred to as a whooping cough. Listen to the audio recording that I attached to the beginning of this post to get an idea of what it sounds like.
During a coughing spell, the person usually gets very red and may even turn blue if the cough is long enough that it makes it hard to breathe. In contrast to other respiratory infections, this one does not present with fever. The stage lasts for weeks, and after this stage the disease begins fading and the third stage comes along.
Convalescent stage – the coughing spells decrease in frequency and severity and the person starts to feel better.

These 3 stages last approximately 6-10 weeks, and that is where the “100-day cough” phrase comes from. Not fun. It is important to remember that sometimes the course of disease may be slightly atypical, when the cough is mostly nagging. Additionally, in people who were previously vaccinated, the disease may be less severe and shorter.
In young infants (under the age of 6 months), and especially in those who are unvaccinated – the disease may be atypical and present with a shorter catarrhal stage, respiratory distress due to the frequent coughing spells, vomiting, cough without the whoop and sometimes episodes of breathing cessation (that may present as the main symptom). The paroxysmal stage may be severe and accompanied by complications, while the convalescent stage may be particularly long.

What are the complications of pertussis?

But Dr Efi, all you’ve told us about is a disease that causes a coughing spell. So maybe it is a little bit unpleasant, but why is it such a big deal? A little bit of a cough, and then it’s over.

Well… not exactly. It depends on who the person is, how old they are, how severe the disease is and, of-course, as usual, how lucky they are.
Some people will have a prolonged disease with a nagging cough for almost 3 months. It is unpleasant to have that and difficult to lead regular daily activities with it.
Among adolescents, adults, pregnant women and elderly people (and the older you are, the higher the risk of getting a severe infection and its complications), there may be complications such as secondary pneumonia, broken ribs, urinary incontinence, loss of consciousness and difficulty sleeping.
In young infants (especially those under the age of 6 months who are unvaccinated), as I already mentioned, the disease itself may be very severe and may lead to sudden infant death syndrome, seizures, meningitis, brain bleeds, secondary pneumonia, a decrease in oxygen saturation in the blood, pulmonary hypertension, bleeding in the eye, hernias and dehydration. And death too.
Around half of the babies who get pertussis need to be hospitalized. Now that’s a lot!
Also, the mortality rate is around 1.6% in infants under the age of 2 months and less than 1.2% in those ages 2-11 months. That means, the mortality for children around the age of 1 year is approximately 1%. In our modern era, that is a very high number.
And these numbers are the precise reason why pertussis is important, and its vaccine – even more so.

How is pertussis diagnosed?

We usually start off with a suspicious clinical presentation, and nowadays, an epidemiological history of an outbreak or known cases within a person’s close vicinity. For example, if a kid presents with a chronic cough (regardless of whether or not it is characteristic of a whooping cough) and you find out that the entire family has been suffering from a cough for the past few weeks, even if none of them have been officially diagnosed yet – the history should raise suspicion.
Making a diagnosis during the catarrhal stage, which is not very different when compared to other viral infections, is clinically difficult and requires a high threshold of suspicion. Sometimes, the blood count (more about this here) may give us a clue, as a high lymphocytic count is characteristic of pertussis infection.

How can we make a clear diagnosis of pertussis?

We are able to do this with the help of two tests:
A PCR test – a swab is taken from the back of the nasal cavity and pharynx. By now, you are all pros when it comes to PCR tests (thanks to COVID-19). The basics behind the pertussis PCR test is no different. PCR is a test that helps us detect the presence of the bacteria’s genetic material. It is a good test to perform during the early stages of the disease, up to two weeks after its presentation (that is, mainly in the catarrhal stage) and if it hasn’t been more than two days since the start of antibiotics.
Serology testing, or a test for the presence of antibodies against the pertussis bacteria. However, this test has several serious limitations:
a. In children under the age of 1 year it is not recommended because the level of antibodies is typically low (therefore, we rely on the PCR test for this age population)
b. In children over the age of 1 year we must wait for at least 2 weeks in order to ensure there has been sufficient production of antibodies to allow for their detection on testing. Also, this test can only be done provided it has been over a year since the child had received their pertussis vaccine, as the vaccine increases the antibody load in the body.
So let me just summarize all the above information.
The PCR test should be done in children under the age of 1 year, at any stage during the disease and in children over the age of 1 year at 2 weeks following the start of the disease.
Serology testing can be done in children over the age of 1 year if it has been two weeks since the start of their illness, depending on when they received their vaccination.

How can pertussis be treated?

First of all, through prevention – that means vaccines. Read more about the available vaccine in the next section.
In those who contract the infection, the treatment is antibiotic medication. The antibiotic of choice is Azithromycin for 5 days. If a person cannot receive Azithromycin there are alternatives – your doctor will know what to prescribe you.
Antibiotics are obviously given to those who test positive for pertussis on PCR or serology testing. However, sometimes, we may choose to start a person on antibiotics before the results are back, when the suspicion is high because of the person’s clinical presentation or history of exposure. It is especially important to start the therapy early in younger infants who are at high risk for developing a severe disease. In those kids, we really do not want to wait for the results.

What is the azithromycin treatment protocol for pertussis?

I often encounter this specific question here and there so I’ve decided to add a section about it.
For children under the age of 6 months, the correct dose of azithromycin for pertussis is 10mg/kg/day, once daily, for 5 days.
For anyone over the age of 6 months, the dose is 10mg/kg/day on the first day (maximal dose is 500 mg) and then 5mg/kg/day, once daily starting the second day, up until the fifth day (maximal dose is 500 mg).
Do not get confused.

Is the treatment for pertussis effective and why so?

When the antibiotics are started early (during the catarrhal stage), they are very effective in treating the clinical symptoms and shortening the catarrhal stage. If they are started when the person is already in the paroxysmal stage, they will not have much of an effect on the course of the disease or on the patient. That is, they won’t really help with the coughing spells. However, they are very useful in reducing the rate of transmission of infection and the spread of the bacteria through coughs.

When is a person who has been treated with Azithromycin considered non-infectious?

Following 5 days of adequate antibiotic treatment, a person is considered non-infectious.

What about the vaccine for pertussis?

I’m glad you asked. The best treatment is always prevention.
This section is slightly advanced, but I trust you guys.
Back in the 1950s, the vaccine that was being administered was the cellular vaccine (DTP) – it was very effective but it had some side effects.
Ever since 2002, we have been administering the acellular pertussis vaccine (DTaP) – it is made up of 2 of the bacteria’s proteins but not the complete bacteria (and that is where the name acellular comes from). This too is an effective vaccine but the immunity it provides weans over the years.
The new vaccine has less side effects but more of a weaning immunity effect.

When and how do children receive their pertussis vaccine?

The vaccine against pertussis is part of the routine vaccinations that are given to children in their first year of life and afterwards during school. It is also recommended for pregnant women (to provide protection for their baby during the period of time immediately after birth, when they are at highest risk, see more below). The vaccine is administered together with the tetanus and diphtheria vaccine, in different combinations.
When is it administered? In most countries around the world, the scheduled times are at ages 2 months, 4 months, 6 months and 1 year. Afterwards, another dose is given between ages 4-6 years and 11-12 years.

What about the administration of pertussis vaccine during pregnancy?

Pregnant women are advised to receive the pertussis vaccine towards the beginning of their third trimester, read more about this here.

Do adults need pertussis boosters?

Sometimes, during outbreaks in certain regions, adults are advised to receive pertussis boosters. I think it is very important for adults who have not received a booster in several years to receive one during outbreaks but I suggest you refer to your national ministries of health for the most current recommendations.

What kind of side effects can the vaccine produce?

There are two important things I would like to point out here:
The cellular vaccine, that is not being used anymore, had a lot more neurological side effects than the one currently in use. Certain associations to this vaccine have stuck since the old vaccine but are not necessarily applicable to the newer one. The acellular vaccine has less side effects. The older vaccine had certain contraindications that are now simply listed under “precautions” and many children who could not receive this vaccine in the past can now enjoy its benefits without any risks.
This vaccine also contains the tetanus and diphtheria vaccines. So, all their side effects are combined. But there are some side effects that are particular to the pertussis vaccine and I will try to point them out below.

Cellular pertussis vaccine adverse effects include:

Local redness, swelling and pain at the injection site. Sometimes, there could be swelling of the entire arm.
General side effects such as fever, restlessness, sleepiness, loss of appetite and allergic reactions, just like any other vaccine/drug. Older children may suffer from headache and fatigue.
A less frequent but more specific side effect would be crying and restlessness that last for hours and make it very difficult to console the child.
Neurological side effects – in the past they used to believe that the vaccine causes an increase in prevalence of seizures but practically speaking such an increase was not evident. Another side effect specific to the pertussis vaccine is a Hypotonic-Hyporesponsive Episode (HHE) which is an episode of general flaccidity and loss of responsiveness.

When should the pertussis vaccine be avoided?

The vaccine should be avoided in children who have a known allergy to one of the vaccine’s components or those who have previously suffered from an allergic reaction to the vaccine. It should also be avoided in children who suffered from a decrease in their platelet numbers following a previous dose of the vaccine.
It should also be avoided in people who suffered from meningitis within one week of receipt of a pervious dose of the vaccine.

When should we be more careful and consult with the pediatrician before receiving the vaccine?

If the child is suffering from a significant febrile infection (not a runny nose and a fever of 37.9°C).
Side effects such as crying, screaming, prolonged restlessness (that last longer than 3 hours) within 48 hours of the dose, that cannot be explained by anything else, also require a consult.
HHE within 48 hours of the dose.
Seizures/febrile seizures (read more here) within 3 days of the dose.

What about children with underlying neurological disorder?

Precautions should be taken in children with progressively degenerative neurological disorders, neurological disorders that are still under investigation or uncontrolled seizures (those with controlled seizures are able to receive it if their neurologist approves).
Children who suffer from static neurologic disorders (for example: cerebral palsy), developmental delay and controlled seizures can receive the vaccine just like any other child.

When is it safe to administer the vaccine?

Mild disease such as runny nose and cough without a high fever.
Children receiving antibiotic treatment.
Children who have a history of febrile seizures (you can read more here) or controlled seizures.
Premature infants without any neurological complications.
Children who have allergies that are not associated with vaccines or a history of allergic reactions evident in first-degree family members.
Children who have first degree family members who have suffered from a complication following administration of the vaccine.
Children who are undergoing surgical procedures (both before and after the vaccine).

What do you do if a child or adult is exposed to someone with whooping cough?

First of all, it is important to understand the extent of the exposure.
An exposure is considered significant if a person was in close contact with a symptomatic individual, such as being in the same room with them for at least an hour or having been exposed to their secretions through a kiss or shared utensils, etc.
Following exposure, the person needs to receive prophylactic treatment. The purpose of this treatment is to prevent the development of disease even if the person has had the infection in the past. Prophylactic treatment includes antibiotics and possibly a vaccine too.
If the person who was exposed is not fully vaccinated – they must catch up on their missed doses (either receive the full series or the booster, depending on their vaccination status).
In addition to this, the individual who was exposed must receive prophylactic antibiotics – usually the antibiotic of choice is Azithromycin for children (and adults) for 5 days, even though adults may be prescribed alternative antibiotics from the macrolide family. If a person is unable to receive macrolides, then trimethoprim-sulfamethoxazole can also be prescribed.
Prophylactic therapy is most effective up to 3 weeks following exposure but may also be considered up to 6 weeks following exposure in individuals who are at high risk such as infants under 1 year, immune-suppressed patients, people with chronic respiratory illness, etc.

What is parapertussis? And how is it related to our topic today?

Parapertussis is a distant cousin of pertussis and belongs to the same family of bacteria as pertussis.
Why am I mentioning it?
Sometimes, the PCR tests that we perform check for the presence of both pertussis and parapertussis and sometimes they may come back positive for parapertussis and negative for pertussis, or positive for both.
Does parapertussis infection require antibiotic treatment? Is the pertussis vaccine effective against it? Do we need to prescribe prophylactic treatment when we are exposed to it, as we do with pertussis?
You will find all the answers to these questions and more in a separate post, in the link here.

In summary, there are several reasons why pertussis is on the rise again in certain areas of the world. These include an old vaccine that had lots of side effects and caused the general public to decline its administration, a new vaccine that is weaker, and super contagious bacteria, that is here to stay.
These are a few of the things I would suggest you do if you’ve read this post and you’ve got a good head on your shoulders:
a. Make sure your children have been vaccinated for pertussis.
b. Ask your parents if they recently received the vaccine, and if not, make sure they do so.
c. Make sure you are fully vaccinated too!
Ain’t nobody wants neither a one-day cough nor a 100-day cough…
Good luck!