Cytomegalovirus retinitis and viral resistance: Prevalence of resistance at diagnosis, 1994

Objective: To determine the prevalence of cytomegalovirus (CMV) isolates resistant to ganciclovir sodium or foscarnet sodium at the time of diagnosis of CMV retinitis, prior to the initiation of therapy. Design: Prospective epidemiologic study. Setting: An acquired immunodeficiency syndrome ophthalmology clinic. Patients: Patients with acquired immunodeficiency syndrome and newly diagnosed CMV retinitis. Intervention: Culturing blood and urine samples for CMV and testing of all positive isolates for sensitivity to ganciclovir and foscarnet. Main Outcome Measure: Prevalence of the following: blood culture isolates resistant to ganciclovir (inhibitory concentration 50% [IC₅₀]>5.5 μmol/L) or foscarnet (IC₅₀>400 μmol/L) and urine culture isolates resistant to ganciclovir or foscarnet. Results: Forty-nine patients were enrolled during a 13-month period. Forty-four patients had blood culture samples that could be evaluated; of these, 66% were positive (59% of patients). Thirty-four patients had urine cultures that were evaluable; of these, 82% were positive (57% of patients). Overall, 78% of patients had either a urine or blood culture sample positive for CMV. No blood culture isolates were resistant to ganciclovir, and only 1 urine culture isolate (2% of patients) was resistant to ganciclovir. Three percent of blood culture isolates and 4% of urine culture isolates (2% and 2% of patients, respectively) were resistant to foscarnet. Overall, 4% of patients had either a blood or urine culture isolate resistant to foscarnet. Conclusion: Resistance to ganciclovir or foscarnet at the time of diagnosis of CMV retinitis is uncommon.