Cytomegalovirus (CMV) is one of the most common opportunistic infections after solid organ transplantation. Cytomegalovirus commonly presents as a viral syndrome characterized by fever, leukopenia, and malaise or can cause tissue invasive disease, such as colitis, pneumonitis, and hepatitis.1
Most transplant centers use antiviral prophylaxis for seronegative recipients of solid organ allografts from seropositive donors (termed donor [D]+/recipient [R]−) for 3 to 12 months depending on the type of transplant.2 Prophylaxis may also be given to patients that receive induction immunosuppression with antithymocyte globulin.3,4 Despite this, viremia and disease remain relatively common; for example, delayed-onset primary CMV infection5 has emerged as one of the most important clinical challenges in the management of CMV D+/R− patients.6-8 After prophylaxis, patients can be monitored with CMV polymerase chain reaction (PCR). However, the optimal duration and frequency of CMV monitoring are not well defined in previous studies.9-11 Seropositive transplant recipients may receive prophylaxis also or undergo a preemptive therapy strategy with regular viral load monitoring.4,12 Due to frequent viral load monitoring, many patients are diagnosed with asymptomatic CMV viremia. The level of viremia at which antiviral therapy is instituted is variable, and consensus in this regard is lacking especially due to the use of nonstandardized viral load assays in many centers.13
Patients with CMV syndrome or end-organ manifestations are termed as having CMV disease. Viremia or disease is generally treated until symptom resolution and viral load clearance (defined as 1 negative viral load or 2 consecutive readings of <137 IU/mL).11 However, many patients will have recurrent CMV viremia and/or disease following initial therapy. The incidence and risk factors for recurrence have only been partially defined. In addition, some experts suggest the use of prolonged antiviral prophylaxis after initial treatment in order to prevent recurrences, especially in special circumstances, such as CMV D+/R− patients.14 However, the clinical benefit of prolonged antivirals is unknown.15,16
To better define the epidemiology and risk factors related to recurrence of CMV after initial treatment as well as to assess the utility of prolonged antivirals, we performed a single-center retrospective review of organ transplant recipients who developed CMV viremia or disease requiring antiviral therapy. Our primary objective was to assess the epidemiology and risk factors for recurrence and whether prolonging antiviral therapy beyond initial virologic clearance prevented recurrence.
MATERIALS AND METHODS
We performed a retrospective cohort study conducted at the University Health Network, Multi-Organ Transplant Program. The program performs approximately 500 organ transplants per year and provides comprehensive follow-up for all patients. Patients were included if they had received an organ transplant as an adult (age ≥ 18 years) and had a CMV viral load greater than 1000 IU/mL or 1110 copies/mL. The review was conducted for new CMV infections between October 1, 2010, and June 30, 2014. This start date was chosen since at this point, the virology laboratory changed the CMV assay from an antigenemia assay to plasma PCR as reported in copies/mL. The laboratory further changed to using a standardized CMV assay reported in IU/mL starting in March 2012. Based on a conversion factor validated in our laboratory, viral loads that were reported in copies/mL were transformed to IU/mL by using a conversion factor of 0.9 (1 copy/mL = 0.9 IU/mL). The assay was subsequently validated against the World Health Organization international standard and all results in this study are reported in IU/mL. The assay has a lower limit of quantitation of 137 IU/mL (equivalent to 100 copies/mL). Results below this threshold are considered negative for the purposes of this analysis. Patients were only included if this was the first detection of CMV since transplant and if antiviral therapy was initiated. Patients were excluded if they had a previous episode of CMV disease or viremia.
Prophylaxis and Treatment Strategies
Antiviral prophylaxis was given posttransplant to all CMV donor seropositive/recipient seronegative (D+/R−) patients for 3 months (liver, heart), 6 months (kidney and kidney-pancreas), and 9 months (lung) posttransplant. Selected CMV seropositive patients received 3 months of antiviral prophylaxis based on additional risk factors including induction therapy with antithymocyte globulin, or if they were a lung, heart, or pancreas transplant recipient. Viral load testing was performed in patients with symptoms, and/or laboratory abnormalities suggested of CMV or in selected patients as part of a preemptive strategy. Therefore, all patients included in this study had either CMV disease or asymptomatic viremia and were treated with antiviral therapy consisting of either valganciclovir or ganciclovir. During treatment, the patients had weekly monitoring of CMV viral loads. (Val)ganciclovir was continued until the viral load was negative on 2 consecutive occasions. After initial therapy, the decision to continue therapy/prophylaxis was dependent on the treating physician, but regardless most patients received regular PCR monitoring (every 1-2 weeks) after initial therapy for at least 3 months. For the current study, to determine rates of recurrence, patients were assessed up to 6 months after discontinuation of antivirals for CMV. This study was approved by the institutional ethics board.
Cytomegalovirus disease, including CMV viral syndrome and tissue invasive disease, were defined according to the American Society of Transplantation definitions for use in clinical studies.17 Cytomegalovirus clearance was defined as 1 negative CMV PCR or 2 consecutive readings of less than 137 IU/mL or less than 100 copies/mL. Recurrence was defined as CMV viral load greater 1000 IU/mL or 1110 copies/mL after initially achieving clearance. Patients were followed up for 6 months after treatment discontinuation to determine recurrence rates. Patients were defined as receiving prolonged antivirals if they received antivirals at any dose after achieving initial clearance.
Viral Load Kinetics
For each patient, the kinetics of viral load clearance was determined by plotting virus loads versus time, where time 0 was the start of treatment. Best-fit lines were used to derive equations describing the decay curves.18 Based on this analysis, the viral load half-life (T-1/2) was calculated using the equation ln2/a, where “a” is the slope of the exponential decay curve. Half-life is defined as the time it takes to decrease the initial viral to 50% after initiation of antiviral therapy. Viral kinetics were only calculated in the subset of patients who had sufficiently frequent viral load testing (at least 3 readings during the treatment phase). This was termed “treatment phase viral kinetics” as it referred to the viral load decline in the initial treatment phase.
Demographics and outcomes were described using descriptive statistics. Risk factors for recurrence were analyzed by χ2 tests for categorical variables and by the Mann-Whitney U test for continuous variables. For the multivariate model, we included all factors with P less than 0.2 on univariate analysis. All statistics were performed using SPSS (v. 22, Chicago, IL).
During the time period 2010 to 2014, a total of 424 organ transplant recipients developed CMV viremia of 1000 IU/mL or greater. Of these, 142 patients were excluded (Figure 1). The reasons for exclusion were primarily because no treatment was initiated (n = 55) or because this was not the first episode of CMV viremia (n = 43). Therefore, the first episode of CMV viremia requiring antiviral therapy was assessed in 282 patients. Patient characteristics are shown in Table 1. Median age was 55 (range, 19-75) years, and the majority of transplant types were kidney (16.0%), liver (29.8%), and lung (42.6%). Most patients received triple immunosuppressive therapy.
Cytomegalovirus viremia or disease occurred at a median of 5.6 (range, 0.63-27.7) months posttransplant and 25 (8.9%) patients developed their first episode of CMV after 1 year posttransplant. Cytomegalovirus-related outcomes are shown in Table 2. A total of 147 (52.1%) patients had symptomatic CMV disease, and the remaining had asymptomatic viremia. After the initiation of treatment, the median time to viral clearance was 28 days (range, 7-337). After initial successful therapy, the incidence of recurrence was 82 (29.5%) of 278 patients at a median of 47 (range, 7-160) days after discontinuation of therapy. Four additional patients recurred while receiving antivirals. In the 82 patients that had CMV recurrence after discontinuing antivirals, the majority of patients (91.5%) recurred within 100 days from end of antiviral therapy, 7 patients developed recurrence between 100 and 180 days. In the total cohort, 226 (80.1%) of 282 patients received prolonged antiviral therapy beyond clearance for a median of 50.5 days (range, 14-911). Patients that received antiviral therapy beyond clearance were more likely to be lung transplant recipients (P = 0.008) (Table 3).
In the total cohort of 282 patients, viral kinetics were calculated for 243 patients (86.2%) based on sufficient viral load testing (Figure 1). The calculated median viral load half-life in 243 patients was 3.34 (range, 1.12-28.7) days. In patients that recurred (n = 81), the median half-life was 4.30 (range, 1.65-28.7) days compared with 2.93 (range, 1.12-28.1) days in those with no recurrence (n = 162) (P = 0.002) (Figure 2). Further, using a cutoff of 3 days, viral load half-life was a significant predictor of recurrence (odds ratio, 0.33; 95% CI, 0.18-0.58) (P < 0.001).
Factors Associated With CMV Recurrence
Univariate analysis was performed to determine factors associated with recurrence (Table 4). A significant association of recurrence was noted with CMV D+/R− serostatus where those with D+/R− serostatus that had a recurrence rate of 39.5% versus 23.9% in those with R+ serostatus (P = 0.005). In addition, receipt of a lung transplant versus other type of organ transplant (P < 0.001) was a significant factor. Viral factors that influenced recurrence included prolonged viral half-life (P = 0.002).
We specifically analyzed immunosuppression variables to determine if this is related to recurrence. Use of mycophenolate mofetil/mycophenolic acid was not associated with recurrence (P = 0.57). In addition, MMF/MPA dosing also did not predict recurrence (P = 0.68). Tacrolimus level also did not predict recurrence (P = 0.55). Prednisone doses ranged from 2.5 to 50 mg daily. There was a trend to CMV recurrence in those on higher doses of prednisone (P = 0.068). Immunosuppression did not differ significantly at the start and end of CMV therapy. In some patients MMF/MPA doses were reduced (n = 110) or discontinued completely (n = 23) during the initial management of CMV, but this was not associated with recurrence (Table 4).
After achieving viral load clearance, prolonged antivirals were given to 226 patients (80.1%). Recurrence occurred in 73 (32.3%) of 226 patients that received prolonged antivirals beyond clearance versus 13 (23.2%) of 56 in those without prolonged antivirals (P = 0.19). However, the time to recurrence from initial viral clearance was greater in the group receiving prolonged antivirals (median, 69 vs 44 days, P = 0.01). We then calculated the time to recurrence after stopping antivirals. In patients that received prolonged antivirals, the time to recurrence from stopping antivirals was 47 (0-150) days compared with 31 (18-160) days in patients with no prolonged antivirals (P = 0.28).
A multivariate model was developed to determine factors independently predictive of CMV recurrence. This included variables with a P value less than 0.2 on univariate analysis. Factors independently predictive of CMV recurrence included longer CMV viral load half-life (P = 0.005), recipient of a lung transplant (P = 0.002), CMV D+/R− serostatus (P = 0.04), and acute rejection (P = 0.02) (Figure 3).
We conducted a retrospective review of a large cohort of solid organ transplantation patients who received therapy for asymptomatic CMV viremia or CMV disease. Our results help better define the epidemiology and risk factors for recurrence. The incidence of recurrence was 29.5% with the vast majority of recurrence occurring within the first 100 days after treatment of the initial episode of CMV. We were able to find several clinical and virologic factors that were associated with an increased risk of recurrence. Clinical factors included CMV D+/R− serostatus, lung transplant, and recent therapy for acute rejection. We also found that treatment phase viral kinetics (as shown by half-life calculation) were associated with recurrence. Because all of these factors are generally known in the individual patient or can be readily determined, this study provides important and relevant clinical utility. Another important finding was the lack of observed benefit to administering prolonged antiviral therapy beyond initial viral clearance. In these patients, it appeared that recurrence occurred but the time to recurrence was further delayed.
Recent studies have indicated that 19% to 27% of all cases of primary CMV disease relapse after a course of antiviral treatment.11,15,16 The majority of patients in these studies have been kidney, liver, and heart transplants; lung transplants were only infrequently represented. In addition, previous studies included only CMV disease, not CMV asymptomatic viremia. Our incidence of recurrence is very similar to that reported in the long-term follow-up of the VICTOR study19 (a randomized trial comparing intravenous ganciclovir vs. oral valganciclovir for treatment of CMV) which showed a 30% rate of virologic relapse. Viral load half-life has been shown to predict recurrence in a previous small study by our group.18 To further add to this, our study showed that a half-life greater than 3 days was associated with recurrence.
Prolonged antivirals can also be used for secondary antiviral prophylaxis. There are very limited data assessing the utility of prolonged antivirals for prevention of recurrent CMV. Guidelines from The Transplantation Society International CMV Consensus Group1 and the American Society of Transplantation2 suggest that prolonged CMV prophylaxis may be beneficial for high-risk populations. The only randomized trial of CMV treatment (VICTOR study) used 1 month of prolonged prophylaxis in all patients, and therefore its utility could not be assessed.19 The potential benefit of prolonged antivirals should be weighed against possible toxicities including leukopenia in up to 28.2% of patients20,21 as well as the significant associated drug costs. Similar to a previous international survey, in our study, 80% of patients received secondary antiviral therapy.14 However, our analysis of recurrence rates found no difference between those that received prolonged antivirals versus those that discontinued antivirals at the time of virologic clearance. This remained true in the multivariate analysis which included transplant type and D)/R serostatus. Recurrences still occurred within 100 days of whenever antiviral therapy was completely discontinued regardless of whether prolonged antivirals were given. An alternative approach may be to monitor with viral load testing at regular intervals up to 100 days after finishing treatment and starting preemptive therapy in those with a positive viral load at a predefined threshold or if symptoms are present. We did not perform specific tests for CMV immune monitoring in this study; however, it is well known that the development of CMV-specific immunity after prophylaxis affects late-onset CMV disease and may also affect recurrence rates.22,23 Also other factors, such as osteoprotegerin, may predict recurrence.24 These factors would be important to study in the future.
Our study had some limitations. First, it was conducted retrospectively and at a single center. Also, frequency of viral load monitoring and the use of prolonged prophylaxis was physician determined. However, the risk factors identified for recurrence did not appear to be influenced by the use or nonuse of secondary prophylaxis based on multivariate analysis. All patients did receive antiviral treatment at least until initial clearance. Also, we assumed both ganciclovir and valganciclovir treatment are interchangeable. This is consistent with previous data19 that show superimposable clearance kinetics with the 2 drugs when used for treatment. We also excluded patients with viremia which resolved spontaneously. These patients did not meet the inclusion criteria of our study and may be at lower risk of recurrence. Therefore, our study cohort may represent somewhat higher risk patients that required therapy. Strengths of our study include the large sample size and the assessment of multiple organ transplant types. In addition, we are able to report the results in IU/mL which means they are readily generalizable to other instiztutions performing PCR with an assay validated to this international standard.
In summary, our study demonstrates that recurrent CMV develops in a significant proportion of patients after treatment of the first episode of CMV viremia/disease. D+/R− serostatus, lung transplant, and treatment phase viral kinetics were all independent predictors of recurrence. We could not demonstrate a benefit for antiviral therapy after initial viral clearance. Because the vast majority of recurrence was in the 3 months after discontinuation of antivirals, an alternative approach may be close virologic monitoring. A prospective randomized trial could help better define the utility of prolonged antivirals.
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