Among the facilities that had undergone at least one inspection in 2010, how many of them have the most serious food safety issues?
in 2010 refers to inspection_date like '2010%'; the most serious food safety issues refers to risk_level = 3
SELECT COUNT(DISTINCT T2.license_no) FROM inspection AS T1 INNER JOIN establishment AS T2 ON T1.license_no = T2.license_no WHERE strftime('%Y', T1.inspection_date) = '2010' AND T2.risk_level = 3