*Purpose: Studies conducted in the northern United States found cytomegalovirus (CMV) disease after liver transplantation follows a seasonal pattern, with increased incidence in Fall and Winter. This has not been evaluated in kidney transplant recipients.

*Methods: Adult patients receiving a kidney transplant at our center in Wisconsin from 1/1/1995-12/31/2018 were evaluated. CMV infection was defined as quantifiable viremia with suspicious clinical factors. Seasons were divided as follows; Winter (December-February), Spring (March-May), Summer (June-August) and Fall (September-November). The primary objective was to evaluate the annual distribution of CMV disease and to assess if this differed significantly based on season.

*Results: There were 6,151 kidney transplants in the study period; 913 patients had 1,492 episodes of CMV infection. Median time from transplant to first detection was 5.51 months (IQR 2.87, 11.7). There was no significant annual periodicity in cosinor analysis (p=0.60). When assessing CMV events where the patient had evaluable serostatus at transplant, the observed incidence exceeded the expected incidence in Winter (+0.7%), Spring (+5.5%) and Fall (+3.4%) and was less than expected in Summer (-9.5%) although this was not statistically significant (p=0.47, Table 1). When evaluating based on serostatus this difference was significant only in those recipients CMV positive at the time of transplant, with summer CMV incidence 21% less than expected (p=0.04, Table 1).

*Conclusions: CMV infection after kidney transplant appears to be less common during the summer season in patients who were R+ at transplant but does not follow seasonal variation in R-. Reasons for this are unclear but could include the positive impact of nature on health, resulting in improved reconstitution of pre-existing CMV cell mediated immunity. These findings may have clinical implications on prophylaxis and treatment, particularly the use of non-pharmacologic strategies to improve response to antiviral therapy.

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