Severe Streptococcus equi Subspecies zooepidemicus Outbreak from Unpasteurized Dairy Product Consumption, Italy

Abstract

During November 2021-May 2022, we identified 37 clinical cases of Streptococcus equi subspecies zooepidemicus infections in central Italy. Epidemiologic investigations and whole-genome sequencing showed unpasteurized fresh dairy products were the outbreak source. Early diagnosis by using sequencing technology prevented the spread of life-threatening S. equi subsp. zooepidemicus infections.

Keywords: Italy; Streptococcus equi subspecies zooepidemicus; arthritis; bacteria; food safety; foodborne outbreak; meningitis/encephalitis; raw milk dairy products; septicemia; streptococci; whole genome sequencing; zoonosis.

Figure 1

Location of residential areas in the province of Pescara and neighboring zones where outbreak cases were found in study of severe Streptococcus equi subspecies zooepidemicus outbreak from unpasteurized dairy product consumption, Italy, during November 2021–May 2022. Sizes of red dots indicate numbers (N = 37) of patients infected by location. Inset shows the outbreak area in the Vestina region of central Italy.

Figure 2

Phylogenetic analysis of Streptococcus equi subspecies zooepidemicus strains in study of severe outbreak from unpasteurized dairy product consumption, Italy. We performed whole-genome sequencing and single-nucleotide polymorphism analysis of 40 S. equi subsp. zooepidemicus strains isolated from clinical and dairy food samples (Table 2). Tree was generated by using the neighbor-joining method. Different colors indicate the different types of samples. Strains were isolated from 2 samples each taken from bulk tank raw milk and cured raw milk cheese. Tree shows clinical specimen sequences clustered with those from dairy products. Scale bar indicates nucleotide substitutions per site.