Correlation between Streptococcus bovis bacteremia and density of cows in Galicia, northwest of Spain

There are few data on the epidemiology of infections caused by Streptococcus bovis (Sb). Some studies suggest that both residence in rural areas and contact with livestock could be potential risk factors.

We performed a retrospective study for the period 2005-2016 of all cases of bacteremia caused by Sb in Galicia (a region in the northwest of Spain). The association between the incidence rate of Sb bacteremia and the number of cattle by province and district was analyzed.

677 cases were included with a median age of 76 years, 69.3% males. The most frequent infections were endocarditis (234 cases, 34.5%), primary bacteremia (213 cases, 31.5%) and biliary infection (119 cases, 17.5%). In 252 patients, colon neoplasms were detected (37.2%). S. gallolyticus subsp. gallolyticus was the predominant species (52.3%). Mortality was 15.5% (105 cases). The annual incidence rate was 20.2 cases/10⁶ inhabitants and was correlated with the density of cattle (p < 0.001), but not with rurality. When comparing the two provinces with a strong predominance of rural population, but with important differences in the number of cattle, such as Orense and Lugo, with 6% and 47.7% of Galician cattle, respectively, the rates were very different: 15.8 and 43.6 cases/10⁶, respectively, with an RR of 2.7 (95% CI, 2.08-3.71). Some districts of the province of Lugo had rates higher than 100 cases/10⁶ inhabitants.

Our study shows a significant correlation between the rates of Sb bacteremia and cattle density, suggesting a possible transmission of Sb from cows to people.