(495) Identification of airway Aspergillus fumigatus infection – use of cough swabs is not a suitable alternative to fungal sputum culture

Background: Aspergillus fumigatus is the dominant fungal pathogen colonizing the airways of up to 50% of adult patients with CF. In addition to the occurrence of ABPA in some patients, the presence of Aspergillus fumigatus has also been associated with increased risk of pulmonary exacerbations and accelerating lung function decline. Detection of Aspergillus colonization/infection is therefore an important feature of routine microbiological surveillance in CF. Since the wide introduction of Elexacaftor/Tezacaftor/Ivacaftor, patients with CF typically describe reduced sputum volumes, and in many cases struggle to produce sputum samples for microbiological culture. Cough swabs are routinely used as an alternative in pediatrics and are known to have reduced sensitivity for bacterial pathogens, but sensitivity for fungal infections is unknown. We aimed to determine whether cough swabs would offer a reliable alternative to sputum culture for the detection of Aspergillus fumigatus in patients with CF.

Methods: This study was performed as a part of the TrIFIC study (www.trific.org).
Adult patients with CF provided spontaneously expectorated sputum samples and cough swabs, collected at the same visit. The sputum sample was prepared using the high-volume culture method and applied directly onto the Sabouraud agar plate culture media. The cough swab was applied directly onto the plate. Both samples were cultured at 30oC for 14 days.

Results: 103 patients have been recruited to date. However, 31 patients (30%) were unable to expectorate any sputum. 23% (24 patients) of this total patient population had growth of Aspergillus fumigatus in either sample.

Table 1. A breakdown of positive results as per whether the patient is CFTR-modulated in those who provided paired sputum and cough swab samples.
This table shows that (although a smaller number of patients) 50% of the unmodulated patients grew Aspergillus fumigatus; compared to 30% of patients who are taking Elexacaftor/Tezacaftor/Ivacaftor.

To date, 63 patients have provided 76 paired cough swab and sputum samples; 14 patients have provided 2 sets of paired samples because we are sampling our patients longitudinally. Of these, 29% (22 patients) had positive sputum cultures for Aspergillus fumigatus. However, only 5 cough swabs had positive cultures for Aspergillus fumigatus, of which 4 were also sputum culture positive. Based on this, sensitivity for sputum to detect Aspergillus fumigatus (identified by any culture method) was 96% and for cough swabs was only 22%.

Conclusions: Cough swabs show a low rate of detection of Aspergillus fumigatus in comparison with sputum. Molecular techniques may be more sensitive but are not validated or widely available. We conclude that cough swabs are unable to reliably detect Aspetgillus fumigatus by culture, and are not suitable for detecting or ruling out fungal infection. We will continue to follow these patients longitudinally and to investigate whether molecular techniques provide additional sensitivity.

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