- Sensitisation to Aspergillus (i.e. the patient has been shown to be reacting to Aspergillus by looking for the present of specific antibodies to Aspergillus in their blood)
- Asthma status (GINA scale)
- Presence of A.fumigatus in sputum (i.e. an indication that Aspergillus is living in their lungs)
The numbers of patients who had Aspergillus fumigatus recovered from their sputum correlated with their level of sensitivity to Aspergillus, suggesting that sensitisation is a consequence of their exposure to the organism living in their lungs - an observation that is not as obvious as it might seem as we all breathe in Aspergillus in the air without necessarily becoming colonised.
Patients sensitised to Aspergillus also had lower lung function, more bronchiectasis, and more neutrophils.
This study concludes that there is an association between Aspergillus in sputum and sensitisation, numbers of neutrophils and reduced lung function.
It is easy to construct a model system using these results whereby an asthmatic person becomes colonised by Aspergillus and as the colonisation proceeds the asthma deteriorates, the latter being a consequence of the former. The earlier paper mentioned seems to show that if that group of people are treated with an antifungal their asthma improves, and that would support this model.
Does Aspergillus therefore cause at least some severe asthma? Perhaps but there is some way to go yet before we can come to firm conclusions. Some centres are already treating fungally-sensitive severe asthmatics (SAFS) with antifungals with good results so the future for this hypothesis does look promising.
NB Colonisation could be defined as an organism living in the lungs without causing noticeable symptoms. This is distinct from inflammation which is where the organism is causing a response from the immune system of the host i.e. inflammation.