How much mold is too much?

In the weeks since Superintendent Renee Foose acknowledged that Glenwood Middle School has had a recurring mold problem, teachers and parents of students have started to come forward with stories of health issues that they believe were caused by mold in the building.
One teacher told of dizziness and heart palpitations at work. Another had breathing problems that led to an emergency room visit. Multiple teachers reported students with nosebleeds, sinus infections and bronchitis. A parent said a mysterious illness that caused her son to miss 16 1/2 days during his sixth-grade year was finally starting to make sense.
The stories paint a picture at odds with assurances from Howard County Public School System officials, who say the middle school's problems have been minimal and were promptly remedied...

 http://www.baltimoresun.com/news/maryland/howard/lisbon-fulton/ph-ho-cf-glenwood-mold-follow-0716-20150715-story.html#page=1