Conflicting advice

Sir, two recently published guidelines give conflicting advice about which dental procedures need antibiotic prophylaxis for preventing endocarditis. The British Cardiac Society report¹ recommends that only some dental procedures associated with high bacteraemia rates require antibiotic prophylaxis for patients with susceptible heart lesions. The British Society for Antimicrobial Chemotherapy guidelines² advise prophylaxis for all dental or gingival manipulations for patients with a few of the highest risk cardiac conditions, but no prophylaxis for patients with moderate risk cardiac lesions. The lack of cover for the latter group of cardiac patients has been commented on elsewhere.³

A new definition of 'significant dental bacteraemia' was proposed in the detailed guidelines of the BCS report,¹ available on The Royal College of Physicians website. This was the demonstration of a statistically significant higher bacteraemia rate post-procedure compared with pre-procedure. However, the main oral organisms associated with endocarditis are viridans streptococci and the pre-procedure incidence of detectable viridans streptococcal bacteraemia by the usual blood culture methods is extremely low. Therefore some studies have omitted pre-procedure blood cultures as they have little relevance. Also, the above definition deals with total bacteraemia rates that include other organisms but does not emphasise that the viridans streptococci are the most important oral organisms. It has been suggested that although the usual blood culture techniques do not detect much bacteraemia pre-procedure the use of lysis-filtration methods are more sensitive⁴ and often detect bacteraemia in subjects before a dental procedure. However, the organisms referred to in one study⁵ were likely skin contaminants, such as coagulase negative staphylococci and propionibacteria, rather than viridans streptococci. A different lysis-filtration study,⁶ not associated with frequent isolations of skin contaminants, failed to detect organisms in any of the 100 pre-procedure blood samples. In this study 85% of subjects undergoing dental extraction had viridans streptococci detected in post-extraction blood cultures. The analysis of the literature quoted in both the British Cardiac Society and BSAC reports was incomplete as many studies were probably unnecessarily excluded as they did not include pre-procedure blood culture data.

Interpretation of the data in the literature may also be difficult because total bacteraemia rates are often quoted for minor dental procedures, and some oral hygiene procedures such as toothbrushing. The actual viridans streptococcal bacteraemia rates are sometimes not given but when they are they are usually very low.⁷ These difficulties with interpretation may result in minimising the risks due to extractions compared with other procedures. This has led to recommendations in the BSAC report² that all dental-gingival manipulations be covered with antibiotics for patients with prosthetic valves and certain other cardiac lesions.

'Significant dental bacteraemia' should mean a high rate of predictable viridans streptococcal bacteraemia associated with a given dental procedure. An example would be an 85% viridans streptococcal bacteraemia rate associated with dental extraction.⁶ In addition, a 'significant dental bacteraemia', in the context of endocarditis, should include consideration of whether such bacteraemias have been followed by endocarditis. Many case reports point to viridans streptococcal endocarditis occurring within two to four weeks of a dental extraction.⁸ Thus dental extraction should be regarded as an important example of a high risk dental procedure on the grounds of significant predictable streptococcal bacteraemia plus frequent associated case reports of post-procedure streptococcal endocarditis.

In conclusion there is a need to challenge the latest suggested definition of 'significant dental bacteraemia' and the BSAC recommendations that all dental or gingival manipulations, including simple dental restoration or fillings, require antibiotic prophylaxis for patients with at risk cardiac lesions. For the reasons stated above only high risk dental procedures should be considered as causing truly significant streptococcal bacteraemias and antibiotic prophylaxis should be reserved for these procedures including extractions, deep scaling and periodontal surgery.