PURPOSE: Cytomegalovirus retinitis is the most common intraocular infection in patients with acquired immunodeficiency syndrome (AIDS). With prolonged suppressive anticytomegalovirus maintenance therapy, resistance occurs in over 25% of patients. We evaluated longitudinal changes in the cytomegalovirus genotype in patients with cytomegalovirus retinitis who developed ganciclovir resistance that was demonstrated in either the blood or urine. METHODS: Patients with AIDS and previously untreated cytomegalovirus retinitis were followed prospectively for the occurrence of resistance while on treatment. Blood and urine specimens were obtained periodically for cytomegalovirus culture according to a predetermined schedule. Positive isolates were tested for phenotypic susceptibility and for mutations in the UL97 and UL54 genes. RESULTS: A mutation conferring resistance to ganciclovir in either the UL97 or UL54 gene was detected in 18 patients. In general, patients with a genotypically resistant virus developed increasing phenotypic resistance over time. There was a suggestion that unless therapy was changed, UL97 mutations tended to persist. In seven of eight patients, the mutations identified in isolates from the blood and urine were identical. In selected patients, there was a suggestion that a mixed population of cytomegalovirus might be present. Progression of the retinitis in an involved eye (15 of 18), contralateral eye retinitis (10 of 11), and extraocular cytomegalovirus disease (5 of 18) occurred commonly among patients with resistant virus. CONCLUSION: Resistance-conferring mutations in the cytomegalovirus genome emerge and may persist when the selective pressure for resistance is maintained. Some patients appear to harbor complex subpopulations of virus with different mutations and different levels of phenotypic resistance. Changes in therapy may result in a shift in virus population and changes in the cytomegalovirus genotype identified.
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