Human cytomegalovirus infection is common in the general population but generally remains silent; the risk of disease is greatest in fetuses and the newborn and in immunocompromised subjects. In Of the 30 samples of DNA from mononuclear cells tested, 25 were positive for cytomegalovirus by the polymerase chain reaction. When the antibody data were decoded we found that all of the samples negative by the polymerase chain reaction were negative for antibody but that five of the 25 samples positive by the polymerase chain reaction were negative for antibody. Three of the five subjects positive by the polymerase chain reaction but negative for antibody were retested after six months. The total antibody test (Abbott) used initially was repeated on the new samples, and another total antibody test (Compenz, Northumbria Biologicals) and an IgG detection test (Medac) were performed; all three tests gave negative results. Serum from these three subjects was also analysed by western blotting with antigens derived from cytomegalovirus AD 169, and two of the samples were designated weakly positive. In all three subjects DNA from mononuclear cells remained positive by the polymerase chain reaction. CommentSeveral subjects considered not to be carriers of cytomegalovirus on the basis of their antibody state were found to be harbouring the virus in mononuclear cells in peripheral blood. Careful handling of the samples and rigorous controls ruled out contamina-M 1 2 3 4 5 6 7 8 9 10 HBVHHV CC BL 171 T M

Summary Eighty-two patients were randomly allocated to receive intravenous acyclovir 5 mg kg 1t.d.s. for 23 days followed by oral acyclovir 800mg 6-hourly for 6 months or matching placebos after allogeneic bone marrow transplantation. Herpes simplex and varicella zoster virus infections were significantly reduced during the period of administration of acyclovir. No reduction in cytomegalovirus infection was demonstrated. The drug was not toxic.The introduction of acyclovir into clinical practice was a useful development in the management of herpesvirus infections (Selby et al., 1979). The drug has been proved to be a highly effective treatment for herpes simplex (HSV) and varicella zoster virus (VZV) infections both in immune compromised and immune competent patients (Meyers et al., 1982;Balfour et al., 1983;Prober et al., 1982; reviewed by Fiddian & Grant, 1985;Prentice & Hann, 1985;Strauss, 1985;Gore & Selby, 1987). The efficacy and lack of toxicity of acyclovir has led to its use to prevent reactivation of herpesvirus infections. It is effective in the prophylaxis of HSV reactivation both in the immune competent patient with, for instance, recurrent genital herpes simplex and in the immune compromised patient, after, for instance, allogeneic bone marrow transplantation (Saral et al., 1981;Gluckman et al., 1983;Wade, 1984; Fiddian & Grant, 1985;Prentice & Hann, 1985; Straus, 1985;Gore & Selby, 1987). However, information about the prophylaxis of VZV infection is much less complete.The concentrations of acyclovir that are required to inhibit VZV in vitro are much higher than those required to inhibit HSV. This observation, together with the limited absorption of acyclovir when given by the oral route (Brigden & Whiteman, 1985), led to doubt about the effectiveness of acyclovir for the oral treatment or prophylaxis of VZV. However, it has been shown that oral acyclovir in high doses is effective in shortening the duration of VZV infections in immune competent patients (Peterslund, 1985;McKendrick et al., 1986).Reactivation of both HSV and VZV after bone marrow transplantation are a common source of morbidity. Up to 70% of patients who are seropositive for HSV infection develop reactivations and 40% of patients get herpes zoster or varicella (Saral et al., 1981;Locksley et al., 1985). However, evidence that long-term oral acyclovir will prevent the development of VZV was inconclusive. We have therefore carried out a prospective randomised double blind trial of intravenous acyclovir given for 23 days followed by oral acyclovir for 6 months in patients following allogeneic bone marrow transplantation. (Freedman & White, 1976).Acyclovir or placebo was administered to adults at a dose of 5mg kg-1 in 100 ml of normal saline infused over 1 h, given 8-hourly starting on the day before transplantation and continuing for 23 days. At that point adults received 800mg tablets 6-hourly for 6 months. Children less than 12 years of age received 250 mg m-2 acyclovir intravenously followed by 400mg orally 6-hourly. Patients wer...

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