Because of developments in surgical techniques, immunosuppression agents, and antimicrobial prophylaxis, solid organ transplantation (SOT) has become increasingly common due to its satisfactory long-term patient and graft outcomes. However, infection remains a common complication for SOT recipients because immunosuppression regimens are required to prevent organ rejection [1]. The risk of infection changes over time, particularly with modifications of immunosuppression. Opportunistic infections typically occur 1 month to 1 year after transplantation because immunosuppression is still weak in the first month. Moreover, recipients with satisfactory allograft function at 1 year posttransplant are likely to tolerate reduced maintenance immunosuppression [1], [2], [3].

Herpes simplex virus type 1 and (HSV-1) and herpes simplex virus type 2 (HSV-2) are α-herpesviruses. In primary HSV infection, epithelial or mucosal cells are the primary targets and latency is then established in nerve root ganglions [4]. A national analysis of common human pathogens in Taiwan demonstrated that the overall seroprevalence rates for HSV-1 and HSV-2 were 63.2% and 7.7%, respectively [5]. The age distribution of HSV infection in adult transplant patients is similar to that of the general population [6]. The infections caused by HSV can be primary or due to reactivation in SOT recipients [7]. HSV seronegative SOT recipients may receive a primary HSV infection from allograft or a natural source after transplantation; however, most HSV infections in SOT recipients, particularly those that occur in recipients undergoing anti-rejection therapy, are reactivations of a previously acquired virus infection [6].

Despite significant advances in SOT in the last four decades, HSV infections remain a leading cause of morbidity and mortality for SOT recipients [8]. Furthermore, SOT recipients shed HSV virus more frequently and experience clinical manifestations of infection more severely than immunocompetent individuals [9], [10]. However, few epidemiological studies have used a nationwide database when examining HSV risk among SOT recipients. This study investigates the risk of HSV infection in SOT recipients from the National Health Insurance Research Database (NHIRD) in Taiwan for the period of 2002 to 2015.