Although patients with bronchiectasis and chronic obstructive pulmonary disease (COPD) release bacteria when they cough, this process does not appear to contribute to the spread of infection to the other people, a study shows.
The study, “Transmission of bacteria in bronchiectasis and chronic obstructive pulmonary disease: Low burden of cough aerosols,” was published in the Respirology journal.
The bacteria Pseudomonas aeruginosa are associated with multiple respiratory conditions including cystic fibrosis (CF), bronchiectasis, and COPD. The transmission of these bacteria through the air followed by another individual inhaling it — aerosol transmission — is thought to be a mechanism by which the infection can spread among CF patients.
It was unclear whether this process also occurs in other respiratory conditions, but researchers at the QIMR Berghofer Medical Research Institute in Brisbane, Australia, have now shown that this is unlikely to be the case.
Cough testing was performed on 16 patients with bronchiectasis and four patients with COPD, all of whom were infected with P. aeruginosa. The test assessed whether the bacteria were released when the patients coughed, and for how long and how far the bacteria could survive in the air.
Results showed that 35% of bronchiectasis and COPD patients (seven out of 20) released aerosols containing the bacteria during coughing.
The distance the bacteria could survive in the air (4 meters) was similar among bronchiectasis, COPD, and CF patients. However, bacteria from bronchiectasis patients survived for a shorter amount of time in the air than bacteria from those with CF — 15 minutes versus 45 minutes.
Furthermore, the amount of bacteria released by coughing was lower in bronchiectasis and COPD patients than in those with CF.
Researchers then performed another analysis to identify the different strains of bacteria released by coughing from 30 patients. The analysis was performed by genotyping, in which the DNA sequences of the different bacterial strains were compared to determine how similar they were.
Results showed that no strains of P. aeruginosa bacteria were the same between patients.
This finding, together with the low number of alive bacteria released by coughing, indicates that aerosol transmission of bacteria is unlikely to spread infection among patients with bronchiectasis or COPD. This is consistent with literature showing that shared bacteria strains are infrequent among patients with these diseases, and that cross-infection only affects a small number of those with bronchiectasis.
The team also identified bacteria strains that are often found in other environments, such as the natural environment and other infections. This may indicate that P. aeruginosa respiratory infections are picked up from the natural environment rather than from another patient with the infection.
“Low viable count of P. aeruginosa cough aerosols, and lack of shared P. aeruginosa strains observed suggest that aerosol transmission of P. aeruginosa is an unlikely mode of respiratory infection spread in patients with bronchiectasis and chronic obstructive pulmonary disease,” the team concluded.