Cancer Treatment Today

Both allogeneic and autologous hematopoietic cell transplant (HCT) recipients are at increased risk for a variety of infections based upon their degree of immunosuppression and exposures, more so the allogeneic transplant recipients.
The types of infections to which these hosts are most vulnerable can be roughly divided based upon their temporal relation to the transplantation:

Preengraftment — less than three weeks
mmediate postengraftment — three weeks to three months
Late postengraftment — more than three months

Unfortunately, infection is reported as the primary cause of death in 8% of autologous HCT patients and 17% to 20% of allogeneic HCT recipients. Many of these are CMV or varicela-zoster infections. High-dose intravenous acyclovir (500 mg/m2 3 times
daily, from day < 5 until day > 30) followed by oral acyclovir (800 mg 4 times daily for 6 months) has been found to effectively reduce the incidence of CMV disease (52%–59% vs. 61%–75%) and increase overall . patient survival. The Infectious Diseases Society of America (IDSA) issued clinical practice guidelines for preventing opportunistic infections among HCT recipients, published in Biol Blood Marrow Transpant ; 2009 ; 15 : 1143 -1238. IDSA does not recommend open ended acyclovir prophylaxis. It says: “Acyclovir prophylaxis should be offered to all HSV-seropositive allogeneic recipients to prevent HSV reactivation during the early posttransplant…Ganciclovir, high-dose acyclovir, and valacyclovir have all shown efficacy in randomized studies in reducing the risk for CMV infection after HCT period (AI). The standard approach is to begin acyclovir prophylaxis at the start of the conditioning therapy and continue until engraftment occurs or until mucositis resolves, whichever is longer, or approximately 30 days after HCT.” It does appears from its discussion in this section that there may be a benefit for a longer patients who are seropositive for CMV or VZV but the guideline does not define how long and does not specifically recommend it.  NCCN does recommend a year of prophylaxis in CMV or VZV infected patients but otherwise only for 30 days.   American Society of Bone Marrow Transplantation and CDC take the same position in an identical language to the ISDA. 

http://www.idsociety.org/Other_Guidelines/

Michael Angarone et al,Prevention and Early Treatment of Opportunistic Viral Infections in Patients With Leukemia and Allogeneic Stem Cell Transplantation Recipients,  J Natl Compr Canc Netw 2008;6:191-201

Prentice HG, Gluckman E, Powles RL, et al. Impact of long-term acyclovir on cytomegalovirus infection and survival after allogeneic
bone marrow transplantation. European Acyclovir for CMV Prophylaxis Study Group. Lancet 1994;343:749–753.

NCCN, Prevention and Treatment of Cancer Related Infections, INF-3, 2012

Marcie Tomblyn, Tom Chiller, Hermann Einsele, Ronald Gress, Kent Sepkowitz, Jan Storek, John R. Wingard, Jo-Anne H. Young, Michael A. Boeckh
Guidelines for Preventing Infectious Complications among Hematopoietic Cell Transplantation Recipients: A Global Perspective Biol Blood Marrow Transplant 15: 1143-1238 (2009) 2009 American Society for Blood and Marrow Transplantation

For Lay summary see here