Nearly half of college students, many stuck at home or in their dorms taking classes mostly online, screened positive for symptoms of depression or anxiety in the fall, according to a new national survey. The prevalence of mental health distress was up slightly from the 44% found last school year.

The Healthy Minds Study surveyed 33,000 students at 36 colleges last fall and found that 47% showed signs of depression, anxiety or both on a standard questionnaire. More than eight in 10 students said their mental health has negatively affected their academic performance on at least one day.

Sarah Lipson, a public health professor at Boston University who co-authored the study, said the negative impact on academics was the highest rate since the annual surveys began in 2007.

“Memory, concentration — those things are really being tested and pulled, and we’re at a deficit for our ability to focus,” said Lipson, who finds many of her students are exhausted and struggling with sleep just days into this new semester.

She attributed the increased anxiety to “the burnout and monotony of what we’ve been doing for nearly a year now,” citing "what this has actually done to our brains and our neural pathways."

For the first time, the survey asked students about loneliness. Two-thirds said they feel isolated from others sometimes or often.

Among students with a positive screen for depression or anxiety, just 40% said they had received any mental health counseling or therapy in the past year. The study said that "treatment gap" was wider than in previous semesters, but not by a large margin.

Correction: A previous version of this story incorrectly stated Sarah Lipson's area of expertise. She is a public health professor at Boston University.