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Chapter 89 Clinical Approach to Infections in the Compromised Host 1451

Defects in the Humoral Immune System disruption of the skin from an indwelling intravenous catheter,
usually with coagulase-negative staphylococci, but also with Coryne-
Immunoglobulin and complement are components of the humoral bacterium jeikeium, Bacillus species, and occasionally atypical
immune system. Immunoglobulin and complement both have associ- mycobacteria.
ated lytic and neutralizing activities. Patients with primary or second- GI mucosal integrity is frequently disrupted by chemotherapeutic
ary defects or deficiencies in humoral immunity are susceptible to agents. Because the GI tract normally is colonized by a multitude of
recurrent pyogenic infections from polysaccharide-encapsulated organisms, this state can lead to infection by streptococci, aerobic
bacteria, such as Streptococcus pneumoniae, Haemophilus influenzae, gram-negative enteric and anaerobic bacteria, and yeast. Mucosal
and Neisseria species. HSCT recipients who continue to receive damage can allow normal flora to invade and become pathogens.
immunosuppressants more than 100 days after transplantation Lower GI ulcerations permit infections by Bacteroides fragilis or
should be given antimicrobial prophylaxis with coverage for encap- Streptococcus bovis. Oral lesions are associated with HSV reactivation,
sulated bacteria until immunosuppression is discontinued. Patients ulceration, and possible bloodstream infection with other common
are also at risk for infections from enteroviruses and Giardia lamblia. oral flora such as α-hemolytic streptococci.
Patients with low levels of circulating IgG may benefit from intrave- The genitourinary tract mucosa may be disrupted by tumors,
nous Ig (IVIg) infusions, although the benefit of using of IVIg invasive procedures, or cytotoxic therapy, with subsequent coloniza-
infusions for routine prophylaxis must be weighed against the expense tion and the potential for local or invasive infection. The most
of this approach. common urinary tract pathogens are enteric gram-negative bacilli,
enterococci, and Candida albicans. Viral reactivation is common,
predominantly from adenovirus and polyomavirus (BK virus), but
Abnormalities in Splenic Function also from the herpesviruses (HSV and CMV).
The lung, genitourinary tract, biliary tract, and auditory canal are
A number of hematologic disorders are complicated by either intrinsic potential sites of mechanical obstruction, increasing the risk for
splenic impairment or splenectomy. The spleen removes organisms localized infection. Obstruction may lead to stasis of local body
from the blood that have been ineffectively opsonized by comple- fluids, with resultant overgrowth of potentially pathogenic colonizing
ment, serving an adjunctive role in fighting infection. It is involved organisms. Patients with chronic hemolytic states are prone to gall-
in the regulation of the alternate complement pathway, and low levels stones that can become a nidus for infection.
of immunoglobulin and properdin have been reported in patients Anatomic alteration can predispose to infection simply by provid-
after splenectomy. Alternate pathway defects may be particularly ing a nidus for growth of organisms. Many patients with sickle cell
important in patients with splenic dysfunction associated with sickle anemia and hemophilia have underlying anatomic abnormalities of
cell disease. the bones and joints as a result of vasoocclusive crises causing infarc-
Asplenic or splenectomized patients are at increased risk for tion of marrow, bony cortex, or synovium. In turn, these changes
serious, frequently fulminant, bacterial infections, primarily for infec- may predispose to infection such as osteomyelitis or arthritis.
tions caused by S. pneumoniae, H. influenzae, Neisseria, Babesia, and Decreased local blood flow and increased bacterial adherence may be
Capnocytophaga canimorsus. The initial presentation of even over- other contributing factors. Foreign bodies, such as prosthetic devices,
whelming infection can be subtle, with fever often the only sign. can lead to persistent infection after even transient bacteremia.
Accordingly, all asplenic patients with underlying hematologic disease
who present with fever should be managed initially as potentially
septic. Overwhelming infection after splenectomy occurs in approxi- Infection in Patients With Acute Neutropenia
mately 7% of postsplenectomy patients, with 50% of infection-related
deaths occurring in the first 3 months. Prophylaxis against pneumo- or Lymphopenia Following Chemotherapy
coccal infection is used for asplenic patients who are small children or Transplantation
or for those with increased immune impairment from malignant
disease. This section outlines predictable infections that can present during
Pneumococcal, H. influenzae type b, and meningococcal vaccines acute profound neutropenia/lymphopenia.
should be administered to asplenic patients. Patients with an intact
spleen may respond better to pneumococcal polysaccharide vaccine
than do splenectomized patients, so immunization is recommended Fever
as early as possible before elective surgery. Additionally, immuniza-
tion before splenectomy can result in protective pneumococcal Despite the specific prophylactic measures directed against common
antibody titers immediately after the operation. For patients with pathogens, many fevers occur in neutropenic patients after transplan-
Hodgkin lymphoma, the antibody response to pneumococcal vaccine tation or chemotherapy. Fever can be divided into three categories:
may not be affected by the timing of immunization relative to sple- infectious fever with an obvious source, infectious fever without an
nectomy. Immunizations reduce, but do not eliminate the risk for obvious source, and noninfectious fever. Risk factor assessment
serious infection with encapsulated bacteria. should include knowledge of the temporal relationship to blood
product infusions; recent exposure to contagious infection; degree of
fever and whether the fever is accompanied by chills, rigors, or dia-
Anatomic Alterations in Host Defense phoresis; and response to antipyretics. Symptom assessment should
include evaluation to assess sinus drainage, sore throat, ear pain,
Immunocompromised patients frequently have disruptions in the cough, sputum production, shortness of breath, abdominal pain,
skin and mucosa, which are important primary physical barriers diarrhea, rash, and dysuria.
against endogenous and exogenous sources of infections (Fig. 89.1). The initial workup of fever in a patient with neutropenia, regard-
Disruption of skin and mucosa may result from invasion by malignant less of whether an infectious or noninfectious source is suspected, is
cells, from the effects of chemotherapy or radiation therapy, from use identical and includes blood culture, culture of symptom-related sites
of invasive diagnostic or therapeutic procedures (e.g., intravenous (e.g., sputum, urine, with/without stool, with/without cerebrospinal
catheters), and from the effects of local infections, such as oral HSV. fluid), review of medication list for potential contributors to drug
Such alterations may provide a nidus for microbial colonization, a fever, review of recent transfusions, chest radiograph, and computed
focus for localized infection, and a portal of entry for systemic inva- tomography (CT) scan of any symptom-related body systems. When
sion. Organisms associated with defects in skin or mucosal surfaces feasible, blood cultures should be drawn through an existing indwell-
depend on the site of breakdown, local colonizing flora, and other ing catheter as well as peripherally because this can facilitate the
factors. Gram-positive organisms are associated with isolated diagnosis of a catheter-related bloodstream infection compared with