WS03.03Capturing a cough. Results of a pilot study to assess the utility of cough plates for microbiological surveillance in CF

Abstract

Objectives

Airway microbiology is increasingly hard to monitor in pwCF on HEMT. This pilot study aimed to evaluate the sensitivity of cough plates in detecting gram-negative bacteria compared to sputum samples.

Methods

Twenty-five adults (14 male, age range 21–55 yrs, FEV1 26–97%, 4/25 non-modulated) underwent airway clearance supervision to collect sputum samples, followed by directed coughs onto pseudomonas-selective and non-selective agar cough plates. If sputum collection failed, sputum induction was performed post-cough plate sampling (n=2). Bacterial infection status was determined by the presence of an infection on any sample in the previous 12months.

Results

Gram-negative bacteria were detected in 18 sputum samples and on 8 cough plates. In 6 cases, the same organism was isolated from sputum and cough plate. In one case, Pseudomonas aeruginosa was cultured at low density solely on cough plate (not on sputum) and differing gram-negative organisms were isolated from the cough plate and sputum in one case. Four samples showed no growth on either sputum or plate.

Over the preceding 12 months, 21 participants (84%) cultured gram-negative bacteria in sputum samples. Based on this, sensitivity of sputum sampling was 72% and cough plates was 32%.

High gram-negative bacterial load in sputum samples (CFU>100) were observed in 9 participants (50%). Cough plates demonstrated lower colony counts overall (range 2–100, median CFU 8.5), with only one plate showing CFU>100. There was no association between high CFU on sputum and detection of the same organism on cough plates.

Conclusions

Although cough plates may serve as a supplemental tool for microbial surveillance in CF adults, their limited sensitivity compared to sputum samples make them insufficient as a stand-alone diagnostic method at the present time. Further refinement of cough plate techniques would be needed to improve the diagnostic utility, particularly if planning to use in adults who are non-productive.