Non-HACEK Gram-Negative Bacillus Endocarditis

Abstract & Commentary

By Dean L. Winslow, MD, FACP, FIDSA Chief, Division of AIDS Medicine, Santa Clara Valley Medical Center; Clinical Professor, Stanford University School of Medicine Dr. Winslow serves as a consultant for Siemens Diagnostics, and is on the speaker's bureau for Boehringer-Ingelheim and GSK. This article originally appeared in the February 2008 issue of Infectious Disease Alert. It was edited by Stan Deresinski, MD, FACP, and peer reviewed by Connie Price, MD.

Synopsis: Of 2761 patients with endocarditis enrolled in a prospective, multinational cohort study, 49 patients with non-HACEK gram-negative endocarditis were identified. E. coli and Pseudomonas aeruginosa were the most common pathogens, and 57% were considered to be health care associated. Fifty-nine percent of cases were associated with prosthetic valves. The mortality rate was high (24%) despite cardiac surgery being performed in 51% of cases.

Source: Morpeth S, et al. Non-HACEK gram-negative bacillus endocarditis. Ann Intern Med. 2007;147:829-835.

Sixty-one hospitals in 28 countries participated in a prospective cohort study of hospitalized patients with definite endocarditis. There were 2761 patients who enrolled between 2000 and 2005. From this cohort, 49 patients with non-HACEK (HACEK stands for: Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, or Kingella) gram-negative endocarditis were identified. Some of the factors differentiating these 49 patients from those with endocarditis due to other organisms included: 59% of the non-HACEK gram-negative cases involved prosthetic valves; 29% had other implanted endovascular devices (pacemakers, implanted cardioverter defibrillators, or aortic stents); 71% had comorbid conditions; 57% were health care associated; only 2 patients (4%) were injection drug users. The following organisms were isolated: E. coli (14), Pseudomonas aeruginosa (11), Klebsiella (5), Serratia (4), and other (15). In patients with non-HACEK gram-negative bacillus endocarditis, 25% had intracardiac abscess vs 14% of patients with endocarditis due to other organisms; in-hospital mortality was 24% vs 17%, respectively. A large number of different antimicrobial regimens were used but all seemed appropriate. A clear advantage of combination antimicrobial vs monotherapy was not seen.

Commentary

Dr. Deresinski (editor of Infectious Disease Alert) and I keep threatening to write an article entitled, "Infectious Disease Truisms Which are not True." One of the truisms we were taught is that non-HACEK gram-negative bacillus endocarditis is largely a disease of injection drug users. This impression was probably due to the publication of several small case series of outbreaks of gram-negative bacillary endocarditis in injection drug users reported from a few large cities during the 1970s and 1980s. This important paper gives a more realistic perspective on this rare disease. Non-HACEK gram-negative bacillus endocarditis should be viewed more properly as predominantly associated with health care-associated acquisition, older age, prosthetic cardiac valves, and other endovascular devices. Paravalvular complications and intracardiac abscess are commonly encountered. Mortality is high despite appropriate medical and surgical therapy.