Proteus mirabilis in Nonpuerperal Breast Infection: A Nosocomial Infection?

I have read with interest the article by Miranda Casas et al. describing the frequent isolation of Proteus mirabilis in patients with nonpuerperal breast infection which has not been reported by other authors, l'z Working in the field of nosocomial infection control, however, was surprised to read the almost casual remark of the potential nosocomial origin of this organism ("... thus suggesting that it was a nosocomial infection."). I believe that there are several epidemiologic considerations to be discussed before the conclusion of a (possible) nosocomial origin can be drawn: What were the characteristics of the patients with P. mirabilis isolated in mixed or pure culture compared with the other patients? Did the affected women have potential risk factors such as carcinoma of the breast which could predispose them to colonization with "unusual" organisms? Did these women perhaps have a prolonged (or repeated) hospital stay with another organism isolated first before P. mirabilis appeared, demonstrating a change in pathogen during hospitalization? Did the pathogens come from an endogenous or an exogenous reservoir? Did the women have prior medical procedures causing transient bacteremia with body flora or, if an exogenous source were likely, what could have been the mode of transmission: contaminated instruments or the hands of staff or anything else? Without considering at least some of these issues, the presumed nosocomial origin ofP. mirabilis breast infections remains vague and un-convincing.