and initiation of appropriate treatment contribute to the high rate of morbidity and mortality of
health care IE (HCIE) (50–52). Tables 2 and 3 summarize the microbiology of CCU IE.
EPIDEMIOLOGY
IE is an infection of the valvular endocardium; rarely of the mural endocardium. The major
types of IE are native valve IE (NVIE), prosthetic valve IE (PVIE), pacemaker IE (PMIE),
intravenous drug abuser IE (IVDA IE) and HCIE. A major focus of this chapter will be HCIE.
The reason for so doing is well expressed by Friedland, “nosocomial endocarditis occurs in a
definable subpopulation of hospitalized patients and is potentially preventable.” It is an
iatrogenic infection for which caregivers must take responsibility. It is defined as a valvular
infection that presents either 48 hours after an individual has been hospitalized or one that is
associated with a health-care facility procedure that has been performed within four weeks of
the development of symptoms. The typical patient is older with a higher rate of underlying
valvular abnormalities. They develop BSIs secondary to a variety of invasive vascular
procedures. HCIE accounts for 20% of overall cases of IE and appears to be on the rise. This is
mainly due to the increase in staphylococcal BSIs that are associated with intravascular line
infections. Type I HCIE is the result of damage to right ventricular structures that is produced
by intravascular catheters (Swan–Ganz lines). Type II HCIE involves the left side of the heart. It
develops secondary to BSIs of any type. Left-sided HCIE the more common because of greater
frequency of abnormalities found on this side of the heart [degenerative valvular disease,
mitral valve prolapse (MVP)]s. In addition toS. aureusand CoNS, gram-negative organisms
and fungi are often isolated from these cases. The mortality rate of HCIE approaches 50% as
compared to 11% for community acquired IE. This is attributable in part to the advanced age of
patients with HCIE. Sixty-four percent of these are older than 60 years. An important exception
to this is that community acquiredS. aureusIE has a higher rate of death than that which
develops in a health care facility. This is probably due to a higher rate of metastatic
complications that go unrecognized and to the prolonged untreated bacteremia in the
community than occurs in HCIE (53–57).
The incidence of IE throughout the world has not changed over the last 50 years. It
ranges from 1.5/100,000 to 6/100000 per population (58–61). Somewhere between 10,000 and
15,000 IE cases occur yearly in the United States. Because of the difficulties in diagnosis, this
figure is at best an estimate. It most likely underestimates the number of cases of HCIE because
of the difficulties in making this diagnosis (see below ‘Diagnosis’). The incidence of IE has not
significantly decreased in the era of antibiotics (1). The ever-expanding field of cardiovascular
surgery and the increasing employment of various intravascular devices accounting great deal
for this phenomenon. Significant variations in the rate of IE exist between nations and within a
country itself. The incidence, type of cases of IE and pathogens that are cared for in a given
health care facility is directly related to the profile of its patients (60,61). Cases of IE are much
more frequent in hospitals that serve a large population of IVDA or patients with congenital
heart disease or those with prosthetic valves. S. aureus is relatively more frequently
encountered in community hospitals, whereas enterococcal IE is usually limited to tertiary
care institutions (62). In areas of the United States with extremely low rates of IVDA,S. viridans
remains the most common cause of IE (63).
IE has become a disease of the older population. In a study of patients in the 1990s, the
mean age was 50 with 35% more than 60 years of age. Presently, more than 50% of cases occur
in those more than 60 years of age (64). This change has been less dramatic in cases of subacute
bacterial endocarditis (SBE), with a current median age of 58. In the 1960s, it was 56 years (63),
with the elderly more susceptible to developing IE. This vulnerability may be related to
nonspecific aging of the immune system (65). Other explanations are based on an increase in
calcific valvular disease among this population (66), the use of cardio- invasive techniques,
intravascular devices, and the rise nosocomial staphylococcal BSIs. Individuals with congenital
heart disease are living longer and frequently require heart surgery (4). In addition, rheumatic
heart disease has essentially disappeared from the developed world. The major exception to
this “graying” trend is IVDA IE. The median age of these patients is approximately 30 years
(67). Table 4 summarizes these trends.
Infective Endocarditis and Its Mimics in Critical Care 223