Course: Opportunistic Fungi in the Immunocompromised Patient
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Epidemiology of Fungal Infection and Disease
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The Environment

The environment is the background on which the host and agent interact and includes demographic, climatic, and societal factors that can influence the spread of infection. In the hospital setting, the surroundings are of major importance in the production of nosocomial infection. Reservoirs for Aspergillus spp and Zygomycetes in hospitals include unfiltered air, ventilation systems, contaminated dust during construction, carpeting, food, water, and even decorative potted plants [11]. In contrast, candidemia is mostly acquired endogenously through prior colonization of the mouth, vagina, skin, and gastrointestinal tract. However, exogenous acquisition of Candida spp has been reported, in particular person-to-person spread of Candida species via the hands of medical personnel [12].

Techniques and therapies used by health-care workers to support critically ill patients often disrupt the first lines of defense that protect humans from invading microorganisms. These include:
  • Barriers afforded by the skin and mucous membranes
  • Low pH generated in gastric acid
  • Normal commensal bacterial flora that compete for nutrients with invading fungal organisms
These defenses are independent of the immune system and although of paramount importance in preventing fungal infection, are often taken for granted (Table 4).

Physical disruption of the barriers by burns, trauma, surgery, or by the placement of intravenous catheters or other invasive devices can provide an entry route for the organisms, such as Candida spp (Table 5) [13].

Catheter-associated infection, including surgically implanted and percutaneous venous catheters, is frequently implicated as a risk factor for candidemia, in particular C parapsilosis. Total parenteral nutrition can predispose patients to disseminated candidiasis. There have been reports of disseminated infection due to Malassezia furfur in patients receiving intravenous lipid emulsions [14]. Infection with Aspergillus due to barrier disruption is uncommon, although case reports have described entry of the organism via the skin at the IV insertion site or at a site of prolonged skin contact with dressings or tapes.

Broad-spectrum antibiotic agents can disrupt the normal bacterial flora and facilitate local overgrowth of normal fungal flora, e.g., Candida species [15] or growth of opportunists, e.g., Aspergillus [16]. This is of particular significance if increased gastrointestinal colonization occurs together with ulcerations after cytotoxic chemotherapy.

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• •   You are at:
Epidemiology of Fungal Infection and Disease
   Interactions between Agent, Host, and Environment
   The Agent
   The Environment
   The Host
   At-Risk Populations
   Spotting the Patient at High Risk
   Timetable of Infection

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Course Number: V035B.043001

This CME Expires on July 1, 2003; no tests will be accepted after this date.

This course is accredited by The University of Pittsburgh School of Medicine, Center for Continuing Education

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