Prevention of infections in the hematopoietic stem cell transplant recipient

History.

Areas of focus for history taking in the recipient and donor are presented in Box 6.1 . A primary goal of this clinical encounter is to elicit any symptoms that may be concerning for the presence of an active infection or recent exposure to an infectious disease that could preclude proceeding to transplantation in the recipient. An equally important goal is to review the recipient’s medical history, social history, and laboratory results from both the recipient and donor to identify gaps in prior preventative measures (i.e., incomplete vaccination), document concomitant comorbidities, identify the presence of latent viruses or colonizing resistant organisms, and document possible social behaviors that may place the patient at risk for future infection.

Transplant information.

Details regarding the type of graft, conditioning regimen, and plans for graft versus host disease (GVHD) prophylaxis are important for understanding the risk of infections in HSCT candidates. Clear documentation of these elements in the pretransplant evaluation makes them easily available if complications arise during the course of transplant.

The type of graft and number of stem cells to be infused should be noted as each of these factors may affect the time to recovery of the immune system after transplant, which will alter infection risk. For example, recovery of neutrophils after an umbilical cord transplantation takes significantly longer compared with receipt of a peripheral stem cell product. Additionally, manipulation of the graft product can also alter infection risk. T-cell–depleted grafts can help reduce the risk of GVHD but will also delay complete immune reconstitution of T-cell function, which can increase the risk for viral or fungal infection in the postengraftment periods. T-cell depletion can be achieved by ex vivo manipulation of the graft product or in vivo administration of a lymphocyte depleting agent such as anti-thymocyte globulin at the transplant. The latter is referred to as serotherapy. Discussions of these graft-specific features with the primary transplant team and the family before transplant can help frame the risk for infection and guide decisions for prophylaxis approaches.

Conditioning regimens include myeloablative conditioning, reduced intensity conditioning, or nonmyeloablative regimens. The risk for toxicity increases with the intensity of the regimen. Myeloablative conditioning regimens are associated with profound immunosuppression and increased risk of mucositis that will predispose a child to bloodstream infections. Radiation-containing regimens increase the likelihood of mucosal and skin breakdown in the recipient. GVHD prophylaxis in HSCT is usually achieved using calcineurin inhibitor–based therapy (i.e., cyclosporine, tacrolimus), sometimes in combination with mycophenolate mofetil. The use of these immunosuppressant therapies increases the risk of infections and has been associated particularly with viral and fungal infections. Use of posttransplant cyclophosphamide for prevention of GVHD may also delay engraftment and count recovery.

When documenting the planned conditioning and GVHD prophylaxis regimens, attention should be given to the possibility of drug-drug interactions with anti-infective agents that might be used in prophylaxis or preemptive strategies. For example, the triazole antifungal class is often leveraged in prophylaxis pathways, but these agents can have significant interactions with many other drug classes, some of which might be used for conditioning or GHVD prevention. Therefore it is important to discuss these details with the transplant team in advance of the transplant.

Physical examination.

The recipient should undergo a complete physical examination, with an emphasis on sites that could become infected or serve as an entry for infection. These include the oral cavity, perirectal region, skin, central venous catheter sites and any foreign bodies, and the upper and lower respiratory tracts. Any signs of active infection should be noted followed by appropriate workup and management. Additionally, these signs of infection should be discussed immediately with the transplant team as they may preclude the ability to move forward with conditioning.

Pathogen-specific testing.

Laboratory testing for evidence of past infectious exposures is performed to detect asymptomatic persistence of certain pathogens in the HSCT candidate and the donor. Some tests are recommended for all HSCT donors and candidates, whereas others depend on epidemiologic risk factors ( Table 6.1 ). Serologic tests are typically used to investigate past exposures for a multitude of pathogens; however, in some cases, screening using polymerase chain reaction (PCR) assays is indicated (i.e., human immunodeficiency virus (HIV) and hepatitis C virus [HCV]). When relying on serology results to determine past pathogen exposures, the clinician must be aware of the possibility for false-positive detection secondary to passive receipt of antibodies (e.g., young infants, recent receipt of immunoglobulin or packed red blood cells). Alternatively, false-negative serology results may be present in patients with an underlying primary immunodeficiency disorder or those who are secondarily immunosuppressed. In these clinical scenarios, a greater reliance on PCR diagnostics may be necessary but does not always allow for the establishment of latent pathogen presence.

Imaging.

Although most HSCT recipients undergo pretransplant imaging, there are no defined standard of care protocols for imaging. Some institutions request imaging of the chest, abdomen, and sinuses for all recipients before transplant; others take a targeted approach based on past infectious history (i.e., fungal infection or pneumonia) and the site of infection. Recipients undergoing autologous or allogeneic HSCT for lymphomas or solid tumors routinely undergo chest and abdominal computed tomography (CT) imaging as part of their disease evaluation. Observational studies suggest that pre-HSCT routine CT imaging of the abdomen may not be warranted in other recipients who are asymptomatic and without previous infectious findings. ^, CT imaging of the sinuses is not routinely recommended as pre-HSCT radiographic findings have not been found to correlate with subsequent development of clinical sinusitis after transplant. Based on these data and to spare patients from unnecessary radiation, the decision to perform CT imaging should be based on a careful risk assessment, history, and physical examination.

Additional evaluations.

Consultation with other specialists may help detect or prevent infections in the recipient. Dental evaluation should be considered for all HSCT candidates to evaluate their oral health and perform any necessary dental procedures to decrease the incidence of oral mucosa–borne infections during periods of mucositis. Otolaryngologic evaluation should be considered in symptomatic patients or those with a history of sinusitis. A direct scope may detect existing infections or anatomic features that may increase risk for infections and identify patients who may need closer follow-up during their transplant course.

History.

Similar to history attainment for the recipient, the goal of the history obtained from the donor is to identify active infection or prior infectious disease exposures that would make the donor ineligible or pose a risk of infection transmission to the recipient. Many of the historical data to be captured for the donor are similar to those collected for the recipient (see Box 6.1 ). A standard approach to capturing this information is important so that no pertinent information is missed. A standardized checklist has been developed by an American Association of Blood Banks (AABB) task force and complies with all regulatory requirements. The checklist is available at the AABB website ( http://www.aabb.org/tm/questionnaires/Pages/default.aspx ) and can be used as a guide for collecting this information. Generally, the donor assessment should identify social risk factors (e.g., intravenous drug use, prior blood transfusions, pregnancies, abortions, and tattoos), document immunization history, and prior travel. Often the donor is not always available for interview by the clinical team; however, clinicians should familiarize themselves with the AABB donor screening tool to know which historical elements need to be assessed from the donors.