Person-to-person transmission of species in the B cepacia complex, including Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia dolosa has been well documented.3 However, at most CF centers, Burkholderia species are detected in a small number of patients, in contrast to P aeruginosa, which chronically infects as many as 80% of adults with CF. Although historically it was believed that P aeruginosa was almost exclusively acquired from the environment, person-to-person transmission has been increasingly described. The earliest reports of cross infection involved CF camps. In one study, investigators described new P aeruginosa infection in eight of 10 individuals. A mucoid P aeruginosa strain was recovered from three of the newly infected individuals, suggesting cross infection from a chronically infected person.4 Another report described the acquisition of P aeruginosa in five previously uninfected individuals attending a week-long camp, and molecular analysis confirmed that these strains matched the P aeruginosa strain isolated from an attendee known to be chronically infected with P aeruginosa.5 Subsequently, investigators from the United Kingdom described recovery of the same strain of P aeruginosa in 55 children cared for at the Liverpool CF center.6 Infection with this strain, now referred to as the Liverpool Epidemic Strain, has been detected in many other centers in the United Kingdom and described in adults with CF in Ontario, Canada.7 We emphasize that shared strains of P aeruginosa can only be reliably identified by molecular testing.