To the Editor: The report by McFarland et al. (Jan. 26 issue)* contributes new information about the acquisition of Clostridium difficile by hospitalized patients. A number of points were omitted from the results that, if available, would be useful in interpreting their data. First, the fact that the late-acquisition group differed significantly from the early-acquisition group in terms of the severity of illness might lead one to propose some protective mechanism whereby severe illness prevents or delays colonization by C. difficile. Logically, one would expect more severely ill patients to receive more intense care and therefore be at greater. © 1989, Massachusetts Medical Society. All rights reserved.