Positive vitreous cultures from eyes without signs of infectious endophthalmitis

There is little information on the rate of false-positive vitreous cultures, because cultures from presumably sterile vitreous are not routinely taken in clinical practice. The objective of this study was to determine the rate of positive vitreous cultures from patients who have no signs of endophthalmitis.

Aerobic cultures from vitreous biopsies were taken from 36 consecutive eyes in which there was no clinical evidence of endophthalmitis. Effluent collected in cassettes during pars plana vitrectomies was processed and cultured in a standard manner. Balanced salt solution was processed intraoperatively through the vitrector and cultured as a negative control.

Positive cultures were obtained in 8 of 36 eyes (22.2%). Coagulase-negative Staphylococcus and Corynebacteria accounted for 7 of the 9 identified organisms. No organism was grown in more than one medium. None of the patients were treated for endophthalmitis after surgery, and none had signs of intraocular infection.

A substantial number of vitrectomy cultures from effluent specimens grow low-virulence organisms in the absence of clinical signs of endophthalmitis. The absence of inflammation at the time of surgery suggests that these positive cultures are contaminants.