Multiple ganciclovir-resistant strains in a newborn with symptomatic congenital human cytomegalovirus infection.

A case of human cytomegalovirus (HCMV) drug-resistance in a congenitally infected newborn is described. Unusual aspects of this case include: (i) the detection of an extremely complex virus population, composed of a mixture of wild-type (wt) and multiple mutant ganciclovir (GCV) and valganciclovir (val-GCV) resistant strains carrying a variety of known mutations in UL97; (ii) the identification of novel UL97 mutations and (iii) the first time detection of combined UL97 drug resistance mutations in the same viral strain. In detail, four known UL97 single-nucleotide mutations (A594T/V, M460V/I, C592G), a new amino-acid substitution (C607S), and a new deletion (597-600) in one of the three UL97 hot spots for GCV/val-GCV resistance (codons 460, 520 and 590-607) were detected. In addition, the combination of M460V + A594V and M460V + C592G was observed for the first time. The emergence of HCMV drug-resistance in symptomatic congenital infections chronically treated with GCV or val-GCV should be taken into account. The immaturity of the neonatal immune system may contribute to selection of complex virus populations in these patients.