If there are any two words that can cause a foaling operation's manager to shudder, they are probably "Rhodococcus equi," since the bacterium is considered the most common cause of severe pneumonia in foals. According to Noah D. Cohen, VMD, MPH, PhD, of Texas A&M University, there's often a push to identify the farm or region where the foals became infected on a premise with cases. In his presentation at the 2003 American Association of Equine Practitioners' Convention, Cohen revealed that with the use of a DNA fingerprinting method, he and other researchers (from Japan, Argentina, and Ireland) discovered that it was not possible to clearly differentiate isolates from different countries, different regions within Texas, or even on the same farm. Therefore, it is nearly impossible to identify where R. equi came from based on the bacterium itself.

R. equi pneumonia can have a devastating impact because prevalence and case fatality rates are often high, and treatment can be prolonged, expensive, and not very successful. The disease also might diminish future performance in the affected animals. Studies have shown that many farms reputed to be affected by the disease can suffer a loss of clients.

Cohen and others wrote in their paper summing up the research, "Understanding epidemiologic characteristics of an organism is essential for developing methods to control and prevent disease caused by infection with that organism," adding that the "mechanisms of transmissions and spread of R. equi are poorly understood."

He and other researchers set out to compare R. equi isolates from affected foals and their environments in Japan, Argentina, Ireland, and the United States, using a specific type of DNA fingerprinting called pulsed-field gel electrophoresis (PFGE). They assessed each strain's genetic similarity with respect to its country of origin and virulence status (whether it causes disease or not). Additionally, they assessed the same on nine farms located across four geographic regions within Texas