Asthma Subgroups: Infection-Induced Asthma

Infection-induced asthma is a subgroup of asthma that may actually be quite common. It is diagnosed when an infection is suspected of causing new-onset asthma, or when infections are your only asthma trigger. It may also be diagnosed when infections are suspected of making asthma more persistent or severe. Here is all you need to know about Infection-Induced Asthma.¹

What is a respiratory tract infection?

They are most commonly caused by respiratory viruses, although some bacterias have also been implicated.  Respiratory tract infections may be diagnosed anytime a respiratory virus or bacteria infects the tissues lining your respiratory tract. This includes your nose, sinuses, throat, and airways. This may include a diagnosis of the common cold, influenza, sinusitis, bronchitis, and pneumonia.

Are asthmatics more susceptible to respiratory infections?

Asthmatics are not more susceptible to developing respiratory infections than the general population. However, when diagnosed with an infection, asthma gene carriers seem to have an elevated risk for developing asthma symptoms as a result.

What is a little history?

The link between asthma symptoms and respiratory infections was first noted during the 1950s, and was attributed to "bacterial allergy." Later studies vindicated most bacteria and implicated respiratory viruses as the most common trigger of asthma symptoms (viruses may be responsible for up to 80% of asthma symptoms).²

What pathogens are involved here?

At the present time, nine families of viruses, and two families of bacterias have been implicated. Here they are, along with the role they are suspected of playing.¹

1. Rhinovirus

   It's the most common cause of the common cold. It usually just affects the upper airways: nose, sinuses, and throat. It has been implicated as a cause of new-onset asthma and is the most common asthma trigger.³

2. Respiratory Syncytial Virus (RSV)

   It causes upper airway cold symptoms in adults, although has been shown to infect the lower airways in small children. Studies seem to suggest that 100% of children are exposed to it by age 2. Some of these children will develop bronchiolitis, and about 10% will develop new-onset asthma. Bronchiolitis is the most common cause of hospitalizations in infants, and these infants are the most likely to be diagnosed with asthma by age three. RSV has long been suspected of triggering asthma symptoms, such as wheezing. So, it has been implicated as both a cause of new-onset asthma and as an asthma trigger.^2,4,5,6

3. Parainfluenza

   These viruses cause lower respiratory tract infections (influenza) in the general population. While they can affect anyone, they are most likely to affect infants, young children, the elderly, those with chronic diseases (like asthma), and those with compromised immune systems. It has been implicated as both a cause of new-onset asthma and as an asthma trigger.⁴

4. Metapneumovirus

   It eluded researchers until 2001 and has been implicated as an asthma trigger. It presents similar to RSV and is the second most common cause of lower respiratory tract infections in children. It also affects adults, particularly the elderly. Lower airway infections have been shown to trigger asthma attacks in those with existing asthma.^7,8

5. Influenza

   It is another cause of lower respiratory tract infections known as influenza. While it does not cause new-onset asthma, it has been shown to trigger asthma symptomseven in those with asthma that is considered controlled. It can also cause pneumonia, and those with asthma are at increased risk for this happening.⁹

6. Coronaviruses

   They are a common cause of upper respiratory tract infections (the common cold) in both adults and children. They have been implicated as an asthma trigger.^3,10

7. Adenovirus

   It has been implicated in the common cold, bronchitis, croup, and pneumonia. It has been suspected as a trigger of asthma symptoms, although not to the degree as the other respiratory viruses.¹⁵ More recent studies seem to show that it’s more likely not so much an asthma trigger as it is an instigator of chronic, more persistent, and severe asthma.

8. Chlamydia pneumoniae

   It’s a bacteria known for causing bronchitis and pneumonia. Studies seem to show it does not cause new-onset asthma nor trigger asthma symptoms. Instead, they seem to worsen airway inflammation in such a way as to make asthma chronic, more persistent, and severe.^12,13,14

9. Mycoplasma pneumonia

   It’s a bacteria known for causing otitis media, pharyngitis, bronchitis and community-acquired pneumonia. While the exact mechanisms are unknown, it seems to be associated with chronic, more persistent, and severe asthma.^14,15

How can infection-induced asthma be prevented?

There really are no definitive methods of preventing yourself from getting respiratory infections, let alone asthma. Still, most experts agree that you can reduce your risk of developing respiratory infections with good hand washing and good overall hygiene.

It's also important to have others who are sick wash their hands frequently and to cover their mouths and noses when they cough or sneeze. It's also a good idea (especially if you have asthma) to get your annual vaccinations.

How can infection-induced asthma be treated?

There is no specific treatment for viruses other than treating symptoms. Bacterial infections may be treated with antibiotics specific to the infecting agent. The best way of treating asthma is with asthma controller medicines. Researchers continue to learn more in an effort to better diagnose and treat infection-induced asthma.

Conclusion

How viruses cause new-onset asthma is something that is still being examined by researchers. They have theories, and I might go over some in a future post (I might also spare you and myself of this, as it appears quite complicated).

In the meantime, it's important for anyone with a diagnosis of asthma to be aware that respiratory viruses and bacteria can trigger infection-induced asthma, and this is true even if you have controlled asthma.