Patients’ Breath May Be Used to Detect P. aeruginosa Infection

Lower levels of certain volatile molecules in the breath of children and adults with cystic fibrosis (CF) can distinguish with good accuracy between those with and without Pseudomonas aeruginosa lung infection, a Dutch study shows.

Notably, a reduction in the levels of a single molecule, called ethyl acetate, was a good predictor of P. aeruginosa infection in pediatric patients, allowing the correct identification of all children positive for P. aeruginosa. In adults, a combination of five molecules was needed to achieve good predictability.

These findings support future studies to further validate ethyl acetate as a potential non-invasive biomarker of P. aeruginosa infection in children with CF, as well as larger studies in adults to better assess the diagnostic potential of these molecules, the researchers noted.

The study, “Targeted exhaled breath analysis for detection of Pseudomonas aeruginosa in cystic fibrosis patients,” was published in the Journal of Cystic Fibrosis.

The characteristic buildup of thick mucus in CF patients’ lungs increases their vulnerability to respiratory infections, with the most common being those caused by the opportunistic bacterium P. aeruginosa, which is highly resistant to antibiotics.

Typically, P. aeruginosa lung infection is detected and monitored via an analysis of patients’ sputum (mucus coughed up from the lungs), “which frequently cannot be obtained in young CF patients,” the researchers wrote.

“Alternatives to sputum cultures are either less sensitive (throat swabs) or highly invasive (bronchoscopy),” and sputum results “take one week and lack in sensitivity, delaying prompt treatment of infections,” the team added.

Notably, sensitivity refers to a test’s true-positive rate, with the complementary feature being sensibility (true-negative rate).

Previous studies have shown that P. aeruginosa infection is associated with the production of several volatile molecules, which can be measured in the breath of CF patients, offering a potential non-invasive alternative for the detection of this serious infection.

However, none of these molecules has been validated as a P. aeruginosa diagnostic biomarker through targeted analysis of breath of CF patients.

Now, researchers from the Amsterdam Mucociliary Clearance Disease Research Group and the Amsterdam University Medical Centers’ Breath Research Group evaluated the use of volatile molecules to identify CF patients with P. aeruginosa lung infection.

By first conducting a comprehensive literature review, the researchers identified 241 volatile molecules associated with P. aeruginosa infection, of which 56 were considered of interest and were measured in the breath of children and adults with CF.

Patients were recruited in the Amsterdam Medical Centers from 2013 to 2014. Based on their sputum/swab analyses, six children and 10 adults were infected with P. aeruginosa at the time of breath analysis, while 15 children and 13 adults had no positive result over the past year.

Lung function was significantly lower in adults positive for P. aeruginosa infection. Children frequently showed co-cultures with Staphylococcus aureus; adults showed a more diverse profile of co-cultures with a variety of pathogens.

Results showed that only 13 of the 56 volatile molecules of interest were detected in the breath of this group of patients, with three of them being significantly different between children and adults.

In addition, a drop in the levels of three volatile molecules — ethyl acetate, 2-butanone, and heptane, 2,4-dimethyl — was significantly associated with P. aeruginosa presence in children with CF.

Notably, a reduction in ethyl acetate levels alone was found to be the strongest predictor of P. aeruginosa infection in pediatric patients.

This link is consistent with previous studies and the team hypothesized that such reduction may be due to the breakdown of ethyl acetate by P. aeruginosa.

“Since sensitivity is the main limitation of cough/throat swabs, the most commonly used culture method in children, our results show additional value of breath screening next to current methods,” the researchers wrote, adding that ethyl acetate “advances as the most important candidate for clinical implementation.”

No single volatile molecule was significantly associated with P. aeruginosa infection in adults, and only a combined reduction of five molecules — ethyl acetate, limonene, 2-pentanone 3-methyl, toluene, and 2-butanone — provided good predictability.

This combination model was able to distinguish between CF adult patients with and without P. aeruginosa lung infection with 70% sensitivity and 100% specificity.

“Targeted VOC [volatile molecules] analysis appears to discriminate children and adults with and without PA [P. aeruginosa] positive cultures with clinically acceptable sensitivity values,” the researchers wrote.

These findings suggest that “a single VOC detection device potentially suffices as screening tool for PA in children, while a more complex detection device might provide a suitable method of PA detection or screening in adults in the future,” they added.

“The diagnostic accuracy for detection of PA that was shown in this study may be considered sufficient to influence clinical decision-making in children, though more studies are required to establish the exact role of exhaled breath analysis in disease monitoring in CF,” the team wrote.

They also noted that additional studies with a larger number of adults with CF are needed to reduce factors potentially affecting volatile molecules and thereby better identify those that may be used to accurately identify patients with P. aeruginosa infection.