Coinfection/virology; Cytosine/analogs & derivatives; Diarrhea/virology; Helper Viruses/physiology; Herpesvirus 6, Human/physiology; Human bocavirus/physiology; Organophosphonates/therapeutic use; Parvoviridae Infections/virology; Roseolovirus Infections/virology; Antiviral Agents/administration & dosage; Antiviral Agents/therapeutic use; Cidofovir; Coinfection/diagnosis; Coinfection/drug therapy; Coinfection/pathology; Cytosine/administration & dosage; Cytosine/therapeutic use; DNA, Viral/analysis; Diarrhea/diagnosis; Diarrhea/drug therapy; Diarrhea/pathology; Helper Viruses/drug effects; Herpesvirus 6, Human/drug effects; Human bocavirus/drug effects; Humans; Infant; Male; Organophosphonates/administration & dosage; Parvoviridae Infections/diagnosis; Parvoviridae Infections/drug therapy; Parvoviridae Infections/pathology; Polymerase Chain Reaction; Roseolovirus Infections/diagnosis; Roseolovirus Infections/drug therapy; Roseolovirus Infections/pathology; Viral Load/drug effects