Is a urinary tract infection with two plus white blood cells serious? The severity of a urinary tract infection is determined by the number of white blood cells in the urine routine. White blood cells equal to two plus signs prove that the urinary tract infection is moderate and can be treated with second-generation cephalosporins and quinolones antibiotics, usually cefuroxime or colistin. The white blood cells in the urine routine is less than one plus sign proves that it is a mild urinary tract infection, greater than or equal to three plus signs is a severe urinary tract infection, so the white blood cells in the urine routine two plus signs belongs to the moderate urinary tract infection, not too serious.