catheter insertion. Within a few days of its placement, a sleeve of biofilmconsisting of fibrin
and fibronectin, along with platelets, albumin, and fibrinogen is deposited on the extraluminal
surface of the catheter. Certain organisms, such asC. albicansor CoNS, also may deposit an
additional layer of glycoccalyx. This composite biofilm protects the pathogens from the host
antibodies and white cells as well as administered antibiotics (86).
For catheters that are left in place for less than nine days, contamination of the
intracutaneous tracts by the patient’s skin flora is the most common source of infection (87). The
bacteria migrate all the way from the insertion point to the tip of the catheter. This results in
extraluminal infections. For catheters of longer duration of surgically implanted catheters,
infection of the hub or lumen of the devices has become the major source of CRBSI (88). By this
time, the biofilm has involved the lumen of the catheter. It is the bacterial flora of health care
workers hands that contaminate the hubs of the intravascular catheters as they go about their
tasks of connecting infusate solutions or various types of measuring devices. The bacteria then
migrate down the luminal wall and adhere to the biofilm and/or enter the bloodstream. For
long-term catheters (those in place for more than 100 days), the concentration of bacteria that
live within the biofilm of the luminal wall of the catheter is twice that of the exterior surface (88).
The major risk factors for hematogenously spread complications ofS. aureusCRBSI are
hemodialysis dependence, MRSA involvement, and duration of symptoms before diagnosis
(89).
The infusate may itself be the cause of BSI. Gram-negative aerobes such asEnterobacter,
Pseudomonas,andSerratiaspecies are the most likely to be involved because they are able to
grow rapidly at room temperature in a variety of solutions.
Because of its hypertonic nature, the solutions of total parenteral nutrition are
bactericidal to most microorganisms exceptCandidaspp. (90). A wide variety of infused
products may be contaminated during their manufacture (intrinsic contamination). These
include blood products, especially platelets, intravenous medications, and even povidone-
iodine (87,91). Up to 1% to 2% of all parenterally administered solutions are compromised
during their administration usually by the hands of the health care workers as they manipulate
the system, especially by drawing blood through it. Most of these organisms are not able to
grow in these solutions except for the Gram-negative aerobes that may reach a concentration of
103 /mL (92,93). This concentration of bacteria does not produce “tell-tale” turbidity in the
solution. The risk of contamination is directly related to the duration of time that the infusate
set is in place.
Arterial catheters have a high rate of CRBSI (greater than 1%). Fifty percent of these are
due to their high degree of manipulation (frequent blood drawing) and the high rate of
contamination of the saline reservoir of this device. The gram-negative aerobes are most
frequently involved (94).
The biofilm of the catheter may be infected during any type of BSI. The infected catheter
may then perpetuate the BSI even though the originating infection has been cured (95).
Central venous catheters that are inserted into the femoral vein have a high rate of
infection than those placed in the subclavian. Internal jugular catheters are at intermediate risk.
More recent data indicates that the infectious complications of hemodialysis catheters may be
the same whether placed in the jugular or femoral vein (96). It would be prudent to avoid the
femoral route unless absolutely necessary.
More than 50% of cases of acute IE have no definable predisposing cardiac abnormalities
(72). Congenital heart disease underlies approximately 15% of all cases of IE. Congenital
bicuspid aortic valve disease may account for 20%of cases of IE in those older than 60 years
(97). Asymmetric septal hypertrophy accounts for 5% of cases (98). The degree of obstruction is
directly proportional to the risk of developing of IE. The greater the pressure gradient, the
greater the chance of infection. Interestingly the mitral valve is most frequently involved,
rarely the aortic. This is due to displacement of the anterior leaflet to the mitral valve by the
abnormal contractions of the septum or by a jet stream affecting the aortic leaflets distal to the
obstruction (99). Other underlying congenital conditions include ventriculoseptal defect,
patent ductus arteriosus, and tetralogy of Fallot (100). Secundum atrial septal defects and
congenital pulmonic stenosis are at negligible risk for the development of IE because of the
minor gradients in pressure observed in these conditions.
226 Brusch