The San Francisco Gate reports that the strain of E. coli O157:H7 isolated from case-patients and bags of spinach during the most recent E. coli outbreak is more virulent than other strains of E. coli O157:H7.

Health officials are working to determine why this particular strain seems to have caused a more severe illness in individuals who consumed contaminated spinach, and whether the molecular make-up of this strain of E. coli differs from other strains of E. coli O157:H7.

Peter Gerner-Schmidt, a scientist at the Centers for Disease Control and Prevention who is investigating the outbreak, agrees that that this strain is probably a more dangerous strain than others. Research is under way to figure out why.