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Infective endocarditis (IE) is a rare infection of the endocardial surface, with an incidence of approximately 4 per 100 000 person-years. Uniformly fatal in the pre-antimicrobial era, the mortality from IE remains high (∼20%). Before the introduction of antibiotics, dentists were called upon to prevent IE in persons with valvar lesions by helping to maintain good oral health. Over the past 60 years, however, antibiotic prophylaxis has been seen as protective, and dental care as potentially hazardous to patients at risk of IE. This view is erroneous, and likely harmful. A call to refocus our energies back on maintaining good oral health is long overdue.
Dental procedures and endocarditis
The relation between oral microbial flora and infective endocarditis was recognised early in the 20th century. With knowledge that disruption of infected oral mucosal barriers results in bacteraemia, medical wisdom in the first half of the 20th century taught that patients at risk of IE “should take all precautions to prevent infections of the teeth . . . and should have existing foci of infection removed.”1 Beginning in the 1930s, though, an expanding body of literature began to document bacteraemia after a wide variety of dental “procedures” in uninfected mouths, including such seemingly benign activities as whistling, brushing teeth, and chewing.
Following several case reports of IE preceded by dental extractions, Northrop and Crowley investigated the relation between dental procedures and IE. In a review of 138 cases of IE treated at one hospital over a 17 year span, they found that only 23 (17%) of these subjects had a history of dental extractions.2 In this same paper, Northrop and Crowley showed a reduction in the incidence of bacteraemia from 12.8% to 4% using sulfathiazole administered to healthy “control” subjects undergoing dental extractions. While acknowledging that transient bacteraemia was only important in the patient with “severe oral sepsis and pyorrhea”, they concluded that “in patients with valvular disease, the possibility of ensuing subacute bacterial endocarditis is greatly diminished by premedication with sulfathiazole” and “immediately a new responsibility arises for the dentist as well as the physician”. These extrapolations of the data in this paper turned history on its ear.
The first recommendations on the use of antibiotic prophylaxis by the American Heart Association were published a little over a decade after Northrop and Crowley's heeding. Recommendations by other reference organisations, such as the British Society for Antimicrobial Chemotherapy, are similar to the most recent revision of the US guidelines.3-5 Despite an attempt to delineate more clearly procedures with and without endocarditis risk, these guidelines recommend antibiotic prophylaxis for many oral procedures. These newer guidelines—despite obvious attempts to address the importance of good oral health care—continue to be viewed as “antibiotic guidelines” which remain inappropriately recommended, inappropriately neglected, or simply not followed.6
Three recent population based studies have challenged the notion that dental procedures cause IE (ironically confirming Northrop and Crowley's earlier findings). Van der Meer and colleagues, looking prospectively at all cases of IE in the Netherlands over a two year period, found that only 64 of 427 (15%) patients hospitalised with IE had any procedure (dental or otherwise) in the preceding three months.7 Using 48 of these 64 patients as cases, they found no significant difference in prior dental procedures compared to matched controls without IE (odds ratio 1.2, 95% confidence interval (CI) 0.03 to 2.3).8 Matching 173 cases of IE according to age, sex, and “group of underlying cardiac conditions”, Lacassin and colleagues performed a prospective case–control study in three regions of France with similar results (odd ratio 1.2, 95% CI 0.7 to 2.1).9 Strom and colleagues, matching for age, sex, and residence, recently found no increased likelihood of prior dental procedures in 273 cases and controls in the greater Philadelphia area (odds ratio 0.9, 95% CI 0.4 to 1.5).10
Antibiotic risks
When antibiotics first came into regular therapeutic use with the introduction of sulfonamides in 1936, they were seen (appropriately) as life saving drugs. However, we now recognise that they also carry risks: 1 in every 10 patients given amoxycillin will develop rash; 1 in every 10 000 patients will develop an anaphylactic reaction; and 1 in every 100 000 will die from an allergic reaction.11-13Gastrointestinal upset, risk of pregnancy (as a result of inactivation of oral contraceptives), and other adverse consequences of antibiotic use are not as quantifiable. A decision analysis looking at antibiotic prophylaxis of IE in persons with mitral valve prolapse demonstrated no mortality benefit from penicillin prophylaxis.14 A more contemporary analysis, looking at modern single dose antibiotic regimens in higher risk patients has not been performed. More importantly, there have been no prospective, controlled studies examining the efficacy or effectiveness of antibiotic prophylaxis for dental procedures.
Antibiotic resistance is another, less obvious, risk to recommending antibiotics for IE prophylaxis. The links between the widespread use of antibiotics and the increasing prevalence of drug resistant organisms are well recognised. Although the scientific community has focused most of its efforts on institutional drug resistance with nosocomial pathogens, evidence is accumulating that ambulatory patients receiving short courses of antibiotics are important reservoirs of drug resistant organisms.15-17 Patients receiving antibiotics for IE prophylaxis are such a reservoir, exemplifying a truth in medical microbiology—that antibiotic resistant populations of bacteria will proliferate under repeated exposure to the same antibiotic (or antibiotic class).
There is little evidence to support the detailed and specific recommendations made by professional organisations concerning the prevention of endocarditis. These recommendations have taken on an aura akin to the Ten Commandments, with comparable success. It is time for the organisations making and periodically updating them to temper the zeal of their statements and to introduce notes of caution based on: (a) the potential public health hazards of their current positions; (b) the unnecessary legal liability of those practitioners who would choose to follow the antibiotic aspects of the guidelines more sparingly or selectively; and (c) the lack of scientific evidence supporting their guidelines. In their turn, the medical, dental, and nursing professions must re-educate themselves to appreciate the potential hazards of widespread and routine use of antibiotics for “prophylaxis” which will follow from adherence to the current guidelines.
Infective endocarditis is seldom associated with dental procedures. The efficacy of antibiotic prophylaxis against IE has not been demonstrated. The use of antibiotics carries risk for both the individual patient (from adverse events) and the community at large (by introducing selective pressure on drug resistant organisms). It is time for a thoughtful review of current practices by both the reference organisations and by health care practitioners.