Aspergillus fumigatus is an aesthetically pleasing micro-organism.
It can also cause a variety of diseases as listed:
- Invasive Aspergillosis
- Allergic Bronchopulmonary Aspergillosis
- Hypersensitivity Pneumonitis
- Atopic Asthma
In most of the clinical diseases above, the isolation, or lack thereof, of Aspergillus fumigatus from sputum bears little relation to the likelihood of the disease being present. I have only seen a handful of each disease entity during my career. However I have seen hundreds of Aspergillus fumigatus isolates from sputum cultures, most of which I am sure are just “colonising” the patient.
So in most cases, what does isolation of Aspergillus from sputum samples mean?
It is my belief that in most cases for Aspergillus to colonise the respiratory tract, there needs to be the presence of “architectural/structural lung disease”. This could be COPD, bronchiectasis, bronchial carcinoma or even cystic fibrosis. There may be the occasional aspergillus isolate in a sputum culture which has resulted from airborne contamination during sampling. However serial isolates of Aspergillus from sputa in a patient with no history of structural lung disease should certainly prompt investigations into this possibility.
There have certainly been studies looking at the prevalence of Aspergillus in patients with structural lung disease, but little that I could find that looks at the specificity of sputum Aspergillus isolates in predicting structural lung disease.
In conclusion I suspect that Aspergillus fumigatus colonisation is quite a strong marker for structural lung disease and would certainly be an area worth studying further, if only I could find the time…..
p.s. I have added a powerpoint presentation on Automation in the Microbiology laboratory, a presentation co-written by myself and Sean Munroe, a microbiology scientist working at Waikato Hospital, Hamilton, New Zealand.