The microbiology and pathogenesis of infective endocarditis.

Some details of 544 episodes of infective endocarditis occurring in 541 patients during 1981 and 1982 are reported. The mean age of patients was 51.6 years and there was a greater proportion of males (2:1). Of the 544 episodes 347 (63%) were due to streptococci, 19% to staphylococci, and 14% to bowel organisms. A wide variety of other organisms were responsible for a few cases, and 10% were culture negative. In 60% the portal of entry of the infection could not be ascertained: 19% were probably of dental origin: 16% arose from the alimentary, genitourinary, or respiratory tracts or from the skin or in association with drug addiction, fractures, or pregnancy; the remaining 5% were related to cardiac or other vascular surgery, cardiac catheterisation, haemodialysis, or other procedures involving the blood stream. Seventy-four (14%) of the 541 patients (mean age 59.0 years) died; the mortality was 30% in staphylococcal cases, 14% in infections due to bowel organisms, and 6% in other streptococcal infections. One hundred and seventy-one (32%) of the patients appeared to have had normal hearts before the onset of illness and another 59 (11%) had cardiac lesions not previously recognised. The aortic valve was the most common site of infection. Ninety (17%) of the patients had prosthetic valves or had undergone other cardiac surgery while 34 (6%) had had a previous episode of infective endocarditis. Nine (1.6%) episodes were not diagnosed until necropsy or operation and 34 (6.3%) required urgent valve replacement.