Letter by Duval et al Regarding Article, “Incidence of Infective Endocarditis Caused by Viridans Group Streptococci Before and After Publication of the 2007 American Heart Association’s Endocarditis Prevention Guidelines”
Authors: Xavier Duval, François Alla, Bruno Hoen
Journal: Circulation (2013)

We have read with great interest the article by DeSimone et al 1 on viridans group streptococcal (VGS) infective endocarditis (IE) incidence before and after the American Heart Association (AHA) IE prophylaxis guidelines were updated in 2007.Given the lack of demonstrated efficacy of IE antibiotic prophylaxis, we think it of paramount importance to identify any increase in VGS IE that would result from the restricted use of IE prophylaxis. 2We recently conducted a study that used methods different from de Simone's (repeated population-based surveys in a large population pool of 8 million inhabitants) but also failed to evidence any increase in the rate of VGS IE in France since IE prophylaxis guidelines were scaled down in 2002. 3 Although we concur with DeSimone's conclusion, we have some concerns about some of their results.First, the number of VGS IE cases on which the authors concluded that the incidence of VGS IE did not increase after 2007 in Olmsted county is extremely low-3 cases over a 3-year period-and is derived from a very small population pool (≈150 000 inhabitants).Any failure to identify IE cases (resulting, for example, from patients' death before IE identification) may have a major impact on incidence estimation.Second, in the next part of the article, the incidence of IE, based on Nationwide Inpatient Sample (NIS) estimations and presumably extrapolated to the whole U.S. population, is not consistent with that observed in Olmsted County.Actually, considering the incidence of IE in Olmsted County during the 2007 to 2010 period (0.77 VGS IE cases per 100 000 person-years), a rough extrapolation to the 209 million U.S. adult population (http://www.census.gov/prod/cen2000/dp1/2kh00.pdf),would lead to 1600 VGS IE cases per year in the United States, which is far from the ≈15 000 VGS IE cases identified annually using the NIS database.This discrepancy may call for different explanations.First, the true incidence of VGS IE during the 2007 to 2010 period in Olmsted County is underestimated; second, the results from Olmsted County cannot be consistently extrapolated to the whole U.S. population; finally, the number of VGS IE cases reported in the NIS database is artificially augmented.Using the NIS system, Federspiel et al 4 estimated that the rate of hospitalizations for IE was between 11.4 and 16.6/100 000 population-years during the 1999 to 2008 period.This rate is much higher than that previously reported for IE incidences (between 3 and 5/100 000 population-years). 5 This could be a result of false IE cases or the multiple counting of single IE cases resulting from patient relocation.This is all the more to be expected in that patients are more and more frequently operated on leading to tertiary-care hospital referral.In conclusion, we encourage great caution in interpreting and comparing data from nonexpert-validated administrative databases or from small population-based studies in which small variations in the number of nonidentified IE cases may have a large impact on results and conclusions.