Cardiac Infections

Infective endocarditis. Streptococci and Staphylococci make up a very large fraction of cases of infective endocarditis, with Streptococci accounting for 50 to 60% of such infections and Staphylococci accounting for another
25%.
The viridans group of Streptococci includes the nutritionally variant organism which now has a new genus. They are now called abiotrophia. Abiotrophia defectivus. These are organisms that look like a viridans or any green hemolytic Streptococci that have unusual nutritional requirements.
Enterococci. Enterococcal infections are much less common in kids then they are in adults, and it is certainly true for endocarditis.
Occasionally, we have seen other Streptococcal organisms. Strep pneumoniae in beta hemolytic Streptococci, such as group C and T, Bs occasionally. So, this is the predominant group of origin. The two situations in which Staphylococci are particularly common, as far as this hemolytic carditis, are in the postoperative patient and in the patient who developed endocarditis in a normal heart.
The other common group of endocarditis agents that must be mentioned are the HACEK group. They account for 5 to 10% of cases of endocarditis.
About 5 % of cases of endocarditis are caused by other agents. Fungi, particularly Candida.
Aerobic gram negatives are not common in endocarditis, except occasionally in line-associated infections and in IV drug abusers; 3 to 5% of endocarditis is culture negative endocarditis and we will talk a little bit about that later on.
Pathogenesis of this disease. There is turbulent blood flow. In pediatric
lesions very often there is a jet effect, and in addition to the jet effect there is also non linear blood flow and eddies of blood. As a consequence of the jet effect, there is often endothelial disruption that occurs, which cumulates the development of the sterile fibrin-platelet thrombus in this area of endothelial damage or disruption. This is an outstanding place for "stray bacteremia" to settle out of the few organisms that become entrapped in this sterile fibrin-platelet fibrin. The slower the blood flow, the greater the opportunity for such organisms to be entrapped.
There are two presentations of infective endocarditis. The patient who
presents acutely is very sick with high fever and very toxic. They may be in congestive failure, and this is the situation where most often one would expect to find Staph aureus as the etiologic agent of the endocarditis. Situations where this presentation is most common is in a patient in the early postoperative phase, who has recently had heart surgery and had lines in place, or the unusual patient who presents with endocarditis with a normal heart without any obvious antecedent event. Other patients who are not postoperative but who have indwelling lines may also become infected with Staph aureus.
The other rather distinctive presentation, and more common presentation of endocarditis, is a much more insidious one. Patients may have low-grade fever or no fever, they are non-toxic. They do not feel very well, they have malaise, decreased energy. These infections are most commonly due to the viridans Streptococci. The HACEK group and fungi also produce infections that are more insidious and subacute in their presentations. Of course, we have patients who do not quite fit exactly in this category.
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