Infections in the Compromised Host

Reading: pg. 423 – 436

Introduction

•      Organisms that usually cause mild, or no, disease in immunocompetent hosts can cause severe morbidity and mortality in compromised hosts

The compromised host

•              types of compromise

–           defects in innate defense mechanisms (fig. 30.1)

•           accidental

•           intentional

–           deficiencies in adaptive response

–           Primary immunodeficiency (congenital)

•           Is inherited

•           exposure in utero

•           idiopathic

•           rare and vary in severity

–           Secondary or acquired immunodeficiency

•           Due to underlying disease

•           Result of disease treatment

•              primary defects in innate immunity

–          Congenital defects in phagocytic cells

•          chronic granulomatous disease

•          no cytochrome b245 means no reactive oxidative intermediates during phagocytosis

–          defects in complement system

•          inability to produce early components in system, C4 and C2, so no C3 convertase

•          Associated with high frequency of extracellular infections

•             secondary defects in innate immunity

–          Due to disruption of mechanical barriers

–          obstruction leads to disruption and infection

•             primary defects in adaptive immunity

–          defect in primary differentiation environment

–          cell differentiation

–          Severe combined immunodeficiency (SCID) - congenital vs. transient

•             secondary defects in adaptive immunity

•             Causes:

–          malnutrition

–         Protein-energy malnutrition (PEM)

–         (fig. 30.7) à inadequate cell-mediated response

–          Infections – are immunosuppressive (HIVàAIDS)

–          Neoplasia à reduced immunoreactivity

–          Splenectomy à impaired humoral response

–          some medical treatments are immunosuppressive

–         Cytotoxic agents

–         Corticosteroids

–         Radiation therapy

•              microbes that infect the compromised host

–          innate compromise: infections due to physical factors

•          burn wound infections

•         provide a nutritious surface for microbial growth

•          traumatic injury and surgical wound infections

•         Destroy integrity of body – make it vulnerable to infections

•          in situ devices (prosthetic valves, pacemakers)

•         Gain access during surgery or subsequent bacteremia

•          compromised clearance mechanism

•         Ciliary escalator damage.

•         Obstruction of urine flow

–          secondary adaptive immunodeficiency

•          hematologic malignancy and bone marrow transplants

•         Leukemia patients

•          solid organ transplants

•         Immunosuppressant drugs given to prevent rejection of grafted organs – makes for a severely compromised host

•          AIDS

•         Infections by opportunistic pathogens due to failing cell-mediated immune response.