Pertussis, more widely known as whooping cough, is an extremely contagious respiratory disease caused by the bacteria Bordetella pertussis (B. pertussis). The main symptoms of this disease are severe coughing fits, followed by a high-pitched "whoop" sound during inhalation. Pertussis is particularly dangerous for infants and young children, often leading to serious complications such as pneumonia, seizures, and in some cases, death. 

The co-occurrence of pertussis with other respiratory microorganisms can extend the severity of illness, complicate diagnosis, and influence treatment outcomes. By examining the interactions between pertussis and other common respiratory infections, such as influenza, respiratory syncytial virus (RSV), the common cold, and various forms of pneumonia, we can better comprehend the difficulties of co-infection dynamics.

Symptoms of pertussis

There are three stages of pertussis symptoms. 

Usually, the initial signs of pertussis are very close to cold symptoms. This includes a runny nose and a sore throat, but not a fever. The symptoms normally last for one to two weeks and you are most infectious at this stage.

After that, in the next stage you might get:

• Coughing fits for a few minutes, usually worse at night
• A ‘whoop’ sound when breathing in between coughs
• Difficulty breathing after coughing
• A thick mucus which could cause vomit

A cough lasting for more than 14 days is more likely to be a pertussis infection. The symptoms listed above can last for 1 to 10 weeks.

In the final stage, you would have continuous improvement with your symptoms and would be in the recovering mode which would take about 2 to 3 weeks. 

Differential diagnosis

Healthcare professionals will need to differentiate between pertussis and other infections to give you a proper diagnosis. Here are a few examples of infectious causes of cough: 

• Bordetella parapertussis - this does not produce pertussis toxins like B. pertussis¹ 
• Mycoplasma pneumoniae
• Chlamydia trachomatis
• Chlamydia pneumoniae
• Adenoviruses
• Respiratory syncytial virus (especially in children)

Examples of non-infectious causes of cough are:

• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Post-infectious cough 
• Gastro-oesophageal reflux disease 
• Underlying lung cancer

Other respiratory infections

Besides pertussis, there are other major respiratory infections such as:

• Influenza 
• Respiratory Syncytial Virus (RSV)
• Common Cold (Rhinovirus)
• Pneumonia (Various Bacterial and Viral Causes)
• Tuberculosis

The similarities between all of them are that they may cause symptoms of cough and fever. They are all infectious and transmitted through airborne droplets and secretions from an infected person who had close contact with you.² 

Next, we are going to look at how pertussis interacts with other respiratory infections. 

Interaction of pertussis with other respiratory infections

Co-infection is defined as an infection of multi-species, or various microorganism species causing the infection. There are not many resources on co-infection but there has been research done on collecting and analysing data to understand the types of co-infections and how they can affect patients. It is shown to decline health in 76% of publications and intensify infections in 57% of publications. Most of the co-infections consisted of bacteria, although the report included all kinds of microorganisms. Co-infecting microorganisms can interact directly with each other or indirectly through your body.³

B. pertussis has been discovered to co-infect with other microorganisms, and studies have been done to try and understand how it interacts with other respiratory microorganisms. 

A study on children hospitalised with severe lower respiratory tract infection (LRTI) was conducted to show the relationship between B. pertussis and other respiratory microorganisms. The results showed that there was a higher risk of worsening disease for those with B. pertussis, especially more so with the children who were additionally detected with C. pneumoniae, M. pneumoniae and parainfluenza viruses. These three microorganisms seemed to be associated with the presence of B. pertussis as they had higher chances of being found together with B. pertussis.⁴

In another study on university students with cough-related diseases, B. pertussis antibodies were found in 15% of them. Out of those students, 17 patients (36%) had antibodies co-detected with influenza B infections, influenza A infections, adenovirus infections, C. pneumonia infections and M. pneumoniae infections. These cross-reacting antibodies of different microorganisms mean that any harmful substance (toxin, virus, etc.) causing your body to make an immune response may seem ‘similar’ to your immune system.^5,6 This shows that B. pertussis can have multi-infections with other respiratory microorganisms resulting in worsened human health.⁷ 

Many healthcare professionals do not realise that B. pertussis is a common cause of community-acquired pneumonia (CAP). Apparently, the complications of having severe pertussis could lead to CAP.⁸ This suggests that B. pertussis has close interactions with pneumonia microorganisms and could impact infants and the elderly in a severe manner.

Based on a study in Chile, the number of co-detection of B.pertussis-infected patients with respiratory viruses was higher during the season of peak viral infections. About half of the patients had co-infections, and they tended to require more respiratory care and nutritional needs.⁹ 

Moreover, those with respiratory viruses have more wheezing compared to those with pertussis, and another differentiating factor is those with pertussis tend to have more cyanosis (blue skin due to low oxygen in the blood), higher white blood cell count and vomiting incidents. This can be useful to diagnose whether or not someone has whooping cough or another type of respiratory disease, or possibly both. However, there has not been much research on the relationship between these two microorganisms and the infection outcomes. 

Treatment considerations

If you think you have pertussis, you may need to follow self-care or treatment strategies depending on how severe the symptoms are.

• Antibiotics
  • For coughs happening in the last 21 days, a macrolide antibiotic is usually prescribed as a first-line treatment. The doses are different according to the age of the patient.
• Self-care
  • Resting, drinking enough fluids and taking painkillers such as paracetamol or ibuprofen should be a priority for the patient. 
  • Taking antibiotics does not mean the cough will be resolved. Pertussis can cause a non-infectious cough that could take a few weeks to clear.
  • The patient should not attend nursery, school or work for 21 days after the start of symptoms if untreated; or until 48 hours of antibiotic treatment has been started.
• Vaccination
  • After recovery, the patient should get vaccinated for whooping cough. Infants and school children get this immunisation in the UK for free. 
  • Those who had the vaccination before being infected by B. pertussis tend to have milder symptoms.
• Hospitalisation
  • For those with severe symptoms like breathing difficulties, unstoppable coughing fits or extreme complications (pneumonia, seizures, etc.), hospitalisation should be arranged.

Currently, there is no research or evidence on the specific treatment of multiple infections including B. pertussis and other respiratory microorganisms. 

Summary

In conclusion, there is evidence that certain microorganisms have close associations with B. pertussis- namely C. pneumonia and M. pneumoniae. They are usually co-detected with B. pertussis in patients with severe symptoms. 

The co-infections are most likely due to your immune system being unable to differentiate the various harmful microorganisms that invade your body.

The results of co-infections with B. pertussis may negatively affect you by worsening your breathing and nutrition in your body. 

However, research has been done to differentiate pertussis and other respiratory illnesses in suspected co-infections. The promising results show that pertussis infections usually cause more cyanosis and white blood cell counts in your body compared to other respiratory illnesses. This could be very helpful for doctors to diagnose patients and make important decisions on treatment. The treatment and management of pertussis mostly include self-care tips, antibiotics, vaccination and hospitalisation depending on your condition. 

There is still a need for further studies on co-infections with B. pertussis. Through this, we could make a difference in reducing the severity of symptoms in those affected by pertussis and other respiratory microorganisms causing multiple infections.