Three more students have been diagnosed with adenovirus at the University of Maryland’s campus in College Park, bringing the number of cases to nine in recent weeks.

A letter sent to students indicated the new cases had been diagnosed over the Thanksgiving holiday, university officials said. In the letter, David McBride, director of the University Health Center, wrote that “none of these new cases has required hospitalization to our knowledge.”

University officials said before Thanksgiving that the campus had recorded six cases of students with adenovirus. One student, 18-year-old Olivia Paregol, died Nov. 18 after being diagnosed with the illness.

Maryland Gov. Larry Hogan this week called Paregol’s death “very concerning.”

Eleven children and a college student have died from complications related to adenovirus. Here’s what to know about the illness. (Amber Ferguson/The Washington Post)

A viral outbreak of the illness also left 11 children dead at a health center in New Jersey.

Adenoviruses are “common causes of colds” and typically “found in significant numbers of people at this time of year,” McBride said. But certain strains of adenovirus can be more serious, according to the website for the school’s health center.

For healthy people, treatment includes rest, fluids and fever-reducing medicine. There is no medication for the infection outside of hospitals.

Officials advised those with chronic medical problems, including diabetes or asthma, or those taking medications that weaken the immune system to seek medical help within 48 hours of developing symptoms.

University officials said they are working closely with state and local health departments to monitor the illness and test those who may have it. To stop the spread, the university is increasing the cleaning of “high-touch surfaces and restrooms” on campus. The dining services department is also increasing cleaning.

The campus earlier in the fall worked to remove mold in some on-campus dorms, but officials said there is “no consistent connection between mold exposure and the incidents of adenovirus infection affecting UMD students.”

The Centers for Disease Control and Prevention recommends other preventive measures, such as frequent hand washing; avoiding touching the eyes, nose or mouth with unwashed hands; and avoiding close contact with those who are ill.