Although cytomegalovirus viral load is commonly used to guide pre-emptive therapy in the post-transplantation setting, few data are available correlating viraemia with clinical endpoints. We therefore investigated the association between cytomegalovirus viral load and mortality in the first year after haemopoietic stem cell transplantation.

In this retrospective cohort study, we included patients from the Fred Hutchinson Cancer Research Center, WA, USA, who received an allogeneic haemopoietic stem cell transplantation between Jan 1, 2007, and Feb 28, 2013, were cytomegalovirus seropositive or had a seropositive donor, and underwent weekly plasma cytomegalovirus monitoring by PCR through to day 100 post-transplantation. Cox proportional hazards models were used to estimate the association of cytomegalovirus viral load at different thresholds with overall mortality by 1 year post-transplantation, adjusting for the use of pre-emptive therapy and other factors such as neutropenia, and graft-versus-host disease.

Of the 1037 patients initially selected for inclusion in this cohort, 87 (8%) patients were excluded because of missing cytomegalovirus testing and 24 (2%) were excluded because of their participation in cytomegalovirus prophylaxis trials. In the remaining 926 patients included in this study, the cumulative overall mortality was 30·0% (95% CI 26·9–33·0) 1 year after haemopoietic stem cell transplantation. 95 patients developed cytomegalovirus disease; death was directly attributable to cytomegalovirus disease in three (1%) of 263 patients who died in the first year after transplantation. A cytomegalovirus viral load of 250 IU/mL or greater was associated with increased risk of early (day 0–60 post-transplantation) death (adjusted hazard ratio [HR] 19·8, 95% CI 9·6–41·1). The risk was attenuated after day 60 (adjusted HR 1·8, 95% CI 1·3–2·3). Similar associations were noted for higher cytomegalovirus viral load thresholds.

Cytomegalovirus viraemia is associated with an increased risk of overall mortality in the first year after haemopoietic stem cell transplantation, independent of the use of pre-emptive therapy, and with evidence of a positive dose-response relationship. These data indicate the suitability of viral load as a surrogate clinical endpoint for clinical trials for cytomegalovirus vaccines, biologics, and drugs.

Merck and Co, National Institutes of Health.