The Centers for Disease Control and Prevention has advised American colleges and universities, and any students or staff arriving from nations hit by the Ebola virus, to take precautions against spreading the disease that go beyond what most schools have done.

In interviews last week, some large universities said they had not adopted any anti-Ebola measures, noting that the C.D.C. had not yet offered them any guidance on the matter. Other colleges said they were asking anyone known to have recently been in the affected countries about possible exposure and potential symptoms, like fever, diarrhea, severe head or body aches, or unexplained bruising or bleeding.

In a new advisory issued over the weekend, the agency recommended that colleges conduct that kind of questioning for anyone who had been in Guinea, Liberia, Nigeria or Sierra Leone in the past 21 days, the maximum incubation period for the virus before symptoms appear.