Incidence of reactivation
Since the earliest descriptions of CMV reactivation in immune competent hosts, there have now been more than 20 studies demonstrating reactivation in non-immune-suppressed patients during critical illness [5–27]. There is significant variability in estimated reactivation rates, most of which may be explained by methodology or kinetics. When these results are summarized, the median/mean rates of reactivation, respectively, are 24 and 23 % (Fig. 1a). It is becoming increasingly apparent that certain patient populations have different risks, with burn patients having much higher rates of reactivation, for example, than cardiac patients [5, 10, 27]. We now know that most reactivation events occur 7–28 days after onset of critical illness [10], likely explaining why studies utilizing very early monitoring (<8 days) showed a 0–1 % reactivation rate [23–26]. In addition, several published studies used viral culture or shell vial methods [13, 14, 21, 22], and while these studies were fundamental to confirm true reactivation by recovering live virus, these methods have lower sensitivity than current PCR or antigenemia-based methodologies. If these early detection and low-sensitivity studies are excluded, it seems that roughly one in three patients with critical illness will have CMV reactivation (Fig. 1b).
Fig. 1 Cytomegalovirus reactivation rates from previously published studies. a All studies included. b Results from all studies using DNA or antigen-based testing and monitoring >8 days