Write SQL query to solve given problem: How many respondents who participated in the survey in 2019 have ever sought treatment for a mental health disorder from a mental health professional?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T1.UserID) FROM Answer AS T1 INNER JOIN Question AS T2 ON T1.QuestionID = T2.questionid WHERE T1.QuestionID = 7 AND T1.SurveyID = 2019 AND T1.AnswerText = 1