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Chapter 89 Clinical Approach to Infections in the Compromised Host 1459

Healthy dogs and cats are considered acceptable pets. However, disruption of mucosal barriers, particular indwelling venous catheters.
the immunosuppressed patient should not be responsible for scoop- Viral infections that reactivate after engraftment often are related to
ing cat litter because of potential Toxoplasma cyst exposure. Similarly, defective T cell-mediated immunity and include CMV, adenovirus,
the patient should not play in sandboxes because these areas are and hepatitis viruses. Outpatient HSCT recipients inhale mold spores
concentrated sites that feral outdoor cats may use as litter boxes. and Pneumocystis cysts from the environment, so common exogenously
Because reptiles of many sorts have been reported to be infected with acquired infections include aspergillosis, mucormycosis, and P. jirove-
Salmonella, patients should not touch these animals or the insides cii (previously carinii). Bacterial infections associated with defective
or outsides of their cages or tanks. The heated water of tropical fish cell-mediated immunity such as pneumococcosis, nocardiosis, and
tanks carry Mycobacterium marinum. Cryptococcus and Chlamydophila atypical mycobacterial disease can also occur in association with
(formerly Chlamydia) psittaci can be transmitted from large pet birds. significant immunosuppression (Fig. 89.6).

Environmental Measures to Prevent Infection Cytomegalovirus

Persons entering the patient’s room to perform an examination or CMV causes significant morbidity and mortality in transplant
touch the patient (including visitors as well as health care workers) patients both directly and because of its immunosuppressive effects
should wash their hands outside the room. Ideally, the institution will that predispose patients to concomitant or sequential infection with
have handwashing sinks in the hallways outside patient rooms for bacterial and fungal pathogens. Use of prophylactic ganciclovir at
this purpose. During respiratory virus season, the infection control engraftment usually is avoided because it leads to myelosuppres-
department often adds extra signs to doorways and other places in sion and possibly a higher incidence of late CMV disease. Instead,
the wards to remind visitors of the importance of handwashing. Staff the patient is treated with ganciclovir when weekly PCR or pp65
and visitors without control of body secretions should not be permit- antigenemia monitoring test meets a positive threshold. Initial viral
ted to have direct patient contact. load levels do not predict disease. CMV infections are treated with
Some infectious situations require special isolation procedures. an induction ganciclovir regimen followed by approximately 6 weeks
Contact isolation (gloves and gowns) is used for patients with adeno- of a maintenance regimen (half the induction dose). The duration
virus, methicillin-resistant S. aureus, or Clostridium difficile infection. of induction (1 to 3 weeks) varies by institution, but in general
Droplet precautions are added to contact precautions for respiratory 1 week is used for low-grade infection, 2 weeks for high-grade
virus or varicella infection. Carriers of vancomycin-resistant Entero- infection, and 3 weeks for end-organ disease. A rising viral load,
coccus are placed in contact isolation until they meet defined criteria when checked weekly during the first month of preemptive therapy,
for discontinuation of isolation. signals the need for continued induction dosing or repeat induction
Laminar airflow is a cumbersome and expensive isolation tech- dosing.
nique that has been largely outmoded with advances in airflow and When the end-organ manifestation of CMV is pneumonitis
isolation technology as well as current antimicrobial therapy. Histori- (recovery of CMV from a deep lung specimen along with an inter-
cally, it has been most commonly used for patients with aplastic stitial infiltrate on chest radiograph), IVIg is added on an every-other-
anemia or those receiving T cell-depleted transplants. day basis for the duration of induction. When CMV manifests in an
High-efficiency particulate air (HEPA) filtration has replaced end organ other than the lungs, use of IVIg is not as clearly useful.
laminar airflow as the means for preventing infection through ventila- Some centers add IVIg when the patient’s total IgG level falls below
tion. With at least 12 air exchanges per hour, HEPA filters are capable 400 mg/dL. Dosing schedules vary from IVIg given once weekly for
of removing particles greater than 0.2 µm in diameter, such as mold 3 weeks to every other day for the duration of induction, similar to
spores. Patients often ask whether they should purchase portable therapy for pneumonitis. Ganciclovir resistance is uncommon, but
HEPA filters for the home or apartment they will occupy after hos- when it occurs, foscarnet or cidofovir may be used.
pitalization. In the broadest sense, this is an extra measure that can
be used on an individual basis. If portable HEPA filters are used, they
should be obtained for each room that the patient will occupy during Varicella-Zoster Virus
the day and night, and each unit should be sized for the individual
room. A beneficial effect of HEPA filtration in the outpatient setting VZV reactivations from latency (zoster) usually are recognized by
has not been demonstrated. their characteristic dermatomal distribution. No temporal pattern is
seen, viremia can occur concurrently, and multiple episodes are pos-
Infection in the Hematopoietic Stem Cell Transplant sible but uncommon. For patients who have been treated for a zoster
episode after HSCT, some centers provide acyclovir prophylaxis until
Recipient Preengraftment 1 year after HSCT. Less common VZV clinical manifestations that
can result in severe infection and may require molecular testing or
The major risk factors for infection in the preengraftment period viral culture for diagnosis include hemorrhagic pneumonia, hepatitis,
include drug-induced mucositis, profound neutropenia, and the central nervous system disease, thrombocytopenia, and retinal
presence of indwelling catheters. Thus the major infections observed necrosis.
in this period are due to bacteria that colonize the skin and GI tract HSCT recipients with a negative or unknown VZV disease history
(e.g., viridans group streptococci and gram-negative bacilli), Candida, and a significant exposure to active varicella are susceptible to primary
and respiratory viruses, especially in the winter months (see Fig. VZV infection. For these patients, varicella-zoster immune globulin
89.6). Reactivation of latent or partially treated fungal infections can should be provided within 96 hours of exposure. Patients with posi-
also occur, with Aspergillus being well recognized. The propensity tive serology can become clinically reinfected after exposure and
of patients to develop such infections has led to widespread use of should be provided with acyclovir prophylaxis; however, such patients
prophylaxis with an antiviral, antibacterial, and antifungal agent do not require varicella-zoster immune globulin.
during this time period.
Epstein-Barr Virus
Infection in the Hematopoietic Stem Cell Transplant
Recipient After Engraftment EBV causes a spectrum of scenarios after stem cell transplantation,
ranging from asymptomatic but detectable viremia, hemophagocytic
Once engraftment has occurred, the major risk factors for infection syndrome, or posttransplant lymphoproliferative disorder (Chapter
include immunosuppression used to treat GVHD and mechanical 52). The incidence of EBV-related complications is higher in