Infective endocarditis (IE) occurs when a circulating microorganism, originating from a portal of entry, encounters a damaged endocardium, whether previously identified or not. It is a rare disease, with an annual incidence of around three cases per 100,000 individuals and a stable in-hospital mortality rate of 20% . Given the high morbidity rate, cost burden and occurrence of post-procedure bacteraemia, IE prophylaxis strategies have long been proposed worldwide to patients with predisposing cardiac conditions (PCC) prior to invasive procedures. Since the early 20th century, clinical findings have associated streptococcal IE, oral portal of entry, bacteraemia and bacterial engraftment on a previously damaged endocardium. It was believed that, using antibiotic prophylaxis, streptococcal engraftment on a damaged endocardium could, and should, be prevented, including after oral procedures responsible for bacteraemia. Prophylaxis guidelines, published from 1954 until the early 21st century were based on this paradigm . They have expanded to embrace any type of procedure (dental, respiratory tract, gastrointestinal, urogenital, etc.) responsible for bacteraemia in all at-risk patients.

In the context of weakly supported guidelines and of oral streptococcal IE incidence decrease, two new sets of scientific data challenge the principles underlying prophylaxis guidelines and explain the general tendency to reduce prophylaxis indications. The first set concerns the relationship between dental procedures and oral streptococcal IE. No prospective, randomized, placebo-controlled study exists on antibiotic prophylaxis. The case-control studies by Strom et al. and Van der Meer et al. provided evidence that dental procedures were unlikely to be a risk factor, whereas in the study by Lacassin et al. , scaling and root canal treatment showed a trend towards a higher risk of IE. The second set concerns the occurrence of transient repeated bacteraemia from everyday life activities (tooth brushing, chewing, etc.). Whereas preventing bacteraemia following invasive procedures was the pathophysiological reasons for antibiotic prophylaxis, everyday life activities were identified as more often responsible for bacteraemia than occasional procedures .

In 2002, the French IE prophylaxis guidelines were the first to call a halt to the systematic use of antibiotic prophylaxis and to restrict the use of prophylaxis to patients at risk of death from IE, that is, patients with high-risk cardiac predisposing factors (in most cases: history of IE, prosthetic valves) and who had invasive dental, respiratory, gastrointestinal and/or genitourinary procedures . In 2007, the American Heart Association (AHA) established new guidelines that were a radical change from the previous US ones published in 1997 : prophylaxis was no longer recommended before dental procedures except for patients with the highest risk of adverse outcome resulting from IE and who had undergone “any dental procedure that involved manipulation of the oral mucosa”. The AHA advised against using prophylaxis in gastrointestinal and urogenital interventions. In 2008, the guidance from the National Institute for Health and Clinical Excellence (NICE) in the UK recommended that IE prophylaxis should no longer be used for all patients and before all procedures, dental and non-dental . In 2009, the European Society of Cardiology guidelines did not follow this radical change, but recommended, as had the 2007 US guidelines , the pursuit of antibiotic prophylaxis for dental procedures solely in patients at highest risk (prosthetic heart valves, congenital heart disease and history of IE). Prophylaxis was no longer recommended for patients at moderate risk or those deemed at low risk (pacemakers and/or defibrillators or who had had previous coronary artery bypass graft surgery) .

IE antibiotic prophylaxis had thus been drastically modified, not because its ineffectiveness had been proven, but because the pathophysiology supporting its use was no longer convincing. There are currently two distinct IE prophylaxis positions: the radical British position based on the lack of evidence of IE efficacy and which abandoned all antibiotic prophylaxis; and the more mitigated one, adopted by the “remaining world”: considering that the lack of evidence is not evidence of ineffectiveness, recommending antibiotic prophylaxis only for a limited patient population, those at very high risk of death in case of IE. These positions have generated considerable reactions, both in favour of maintaining the antibiotic prophylaxis because there is no tangible evidence for a change, and in favour of an abandon or a limitation because there is no tangible evidence for its continuation .

However, the adequacy of these IE prophylaxis guideline modifications remains questionable: a significant increase in IE incidence after scaling down prophylaxis use would argue for its efficacy, whereas a stable or decreased IE incidence would tend to support the appropriateness of prophylaxis modifications. In 2011, Thornhill et al. reported an evaluation of guideline modifications. They conducted an epidemiological study in England after the 2008 NICE guidelines, using the 2000–2010 national data on inpatient hospital activity . During the 2 years following the guideline changes, antibiotic prophylaxis prescription decreased by 78%, without evidence of an upward trend in IE cases (in particular of oral streptococcal IE) or in death rate. In France, results of three population-based surveys showed that streptococcal IE incidence, with or without previously identified native PCC, did not increase between 1999 and 2008, following 2002 guideline modifications . This lack of increase was also reported in the US by Desimone et al. in Olmsted County and in the US paediatric population by Pasquali et al. .

Two different IE patterns can be distinguished:

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  streptococcal community-acquired IE for which antibiotic prophylaxis is recommended in high-risk patients who undergo a dental procedure (with the notable exception of the NICE guidelines);

  
  
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  staphylococcal community and healthcare-acquired IE for which no specific prevention recommendation exists.

Present data establish that the recent modifications in antibiotic prophylaxis strategy are not at the origin of a short term re-emergence of IE due to dental microorganisms. Before continuing to limit antibiotic prophylaxis use and recommending — as NICE did — that no antibiotic prophylaxis be used in any patients, it would be wise to continue monitoring the epidemiological disease characteristics with population-based studies, to better understand the relationship between oral flora, dental status and at-risk procedures, and to evaluate doctors’ and dentists’ compliance with the guidelines. Global hygiene measures for everybody, including oral and skin hygiene, to minimize the risk of community-acquired and healthcare facility-acquired bacteraemia must be reinforced, and must target patients both with and without PCC, and be included in a global strategy of infection prevention.

IE co-evolved with socioeconomic changes and medical progress, leading to an increase in onset age, comorbidities, intracardiac devices and of staphylococcal IE. IE antibiotic prophylaxis has been drastically modified during the last 10 years, and there are currently two opposite strategies, both of then leading to a major reduction in antibiotic prophylaxis indications. To date, this change has not given rise to an increase in oral streptococci IE, which supports, a posteriori, the reduction of its use and allows us to claim that “we were right”. A better understanding of the physiopathology of IE and the characterization of the new valvulopathies should help to better target patients not previously considered at risk of IE. Nevertheless, epidemiological surveillance is vital in order to observe rapid changes in the profile of the disease and to modify, if necessary, recommendations for better prevention.