Association between rural residency, group D streptococcal endocarditis and colon cancer?

Abstract

We read with interest the article in CMI by Giannitsioti et al. [1] that analysed the link between rural residency and a higher proportion of group D streptococcal infective endocarditis (GDS IE). In the last 20 years (1988–2007), we have diagnosed 68 cases of GDS IE, with 44 (64.7%) of these cases occurring in the last 6 years. These cases comprised 26% of the total number of cases of infective endocarditis (IE), and were associated with biotype I and colon tumours in 95% and 57% of patients, respectively. In total, 56% of the patients with GDS IE resided in rural areas, as compared to 35.6% of the 45 patients diagnosed with IE caused by viridans group streptococci during the same period (p <0.02). Group D streptoccus was the primary cause of IE in our centre, with a high and increasing incidence. This, together with a greater frequency in rural areas, is very similar to the situation reported in France. However, overall, group D streptococcus constitutes a relatively infrequent cause of IE in Spain, perhaps because the majority of reports come from urban areas such as Madrid and Barcelona [2,3]. The association between rural residency and a higher incidence of GDS IE might be attributed, at least in part, as suggested by Giannitsioti et al. [1], to environmental factors, including dietary habits or contact with animals. Group D streptococcus is an intestinal bacterium that is isolated frequently from human specimens, as well as from the faeces of calves, young cattle and dairy cows [4]. Our region is one of the major areas in Spain for the production of cattle and dairy products, and the majority of the population lives in the countryside in close contact with cattle. Perhaps the local population has a higher rate of group D streptococcus faecal carriage, which, in combination with other factors that have been insufficiently researched, e.g., a change in the virulence of certain strains, changes in dietary habits, and an elderly population with a high number of degenerative valvulopathies, could favour this high incidence of IE. Another question is whether these environmental factors might be associated with a higher incidence of colon tumours in these patients, given the association of this cancer with bacteraemia caused by Streptococcus bovis biotype I [5]. Accordingly, we analysed 130 cases of bacteraemia caused by group D streptococcus (with and without IE) according to biotype and rural residency. Eighty-nine involved biotype I (53% with colon cancers), and 41 involved biotype II (7% with colon cancers, p <0.0001). However, rural residency was significantly more frequent in patients with biotype II (80.5% vs. 47%, p <0.0001). Further epidemiological research is needed to explain these findings.