Canadian researchers have identified a common transmissible strain of the bacteria P. aeruginosa among cystic fibrosis (CF) patients in Canada, suggesting that cross-infection has occurred widely between CF centers in the United Kingdom and Canada. Infection with this strain among Canadian CF patients has been associated with an increased risk of death or lung transplantation. The findings were published in JAMA.
The researchers conducted the study to determine whether patients with CF in the province of Ontario were infected with transmissible strains of P. aeruginosa, and if so, to determine the prevalence of infection and the incidence rates of new infection with these strains. Transmissible strains of P. aeruginosa have not previously been described in North American patients with CF.
The study included adult patients cared for at CF clinics in Ontario, with enrollment from September 2005 to September 2008. Sputum was collected at the beginning of the study, 3 months, and yearly thereafter for 3 years, and P. aeruginosa isolates were genotyped. Vital status (death or lung transplant) was assessed for all enrolled patients until December 31, 2009.
The researchers found that of the 446 with CF studied, 102 were discovered to be infected with one of two common transmissible strains of P. aeruginosa at study entry—a sizable minority of adult Canadian CF patients living the province of Ontario.
The study’s authors write, “Sixty-seven patients were infected with strain A (15%), 32 were infected with strain B (7%), and three were simultaneously infected with both strains (0.6%). Strain A was found to be genetically identical to the Liverpool epidemic strain [a strain first identified in 1996], but strain B has not been previously described as an epidemic strain. The incidence rate of new infections with these two transmissible strains was relatively low. Compared with patients infected with unique strains of P. aeruginosa, patients infected with the Liverpool epidemic strain (strain A) and strain B had similar declines in lung function.”
Death or lung transplant occurred at twice the rate in patients (n=13) infected with P. aeruginosa strain A (18.6%), compared to patients (n=19) infected with unique strains (8.7%).
“Infection with P. aeruginosa strain A was associated with a greater 3-year risk of death or lung transplantation compared with patients infected with unique strains. Infection with P. aeruginosa strain B was not significantly associated with a greater 3-year risk of death or lung transplantation compared with patients infected with unique strains,” note the researchers.
According to the researchers, the most prevalent transmissible strain found was the Liverpool epidemic strain—which was found to infect more than 15% of Ontario patients. This same strain is known to infect approximately 11% of CF patients who receive their care in one of 15 CF clinics in England and Wales. This study is the first to suggest that common strains of P. aeruginosa are shared among patients located on different continents. The data suggests that cross-infection with P. aeruginosa has occurred widely both within Ontario and between CF centers in the United Kingdom and Canada.
The researchers believe cross-infection with transmissible strains of P. aeruginosa may be the result of close patient-to-patient contact among infected and noninfected patients, including from airborne transmission of P. aeruginosa via coughing.
Currently, it is unknown if infection with the Liverpool epidemic strain or with other transmissible strains of P. aeruginosa is prevalent among patients in the United States.