(Bloomberg) — U.S. health officials issued stricter guidelines that say people with direct exposure to the Ebola virus should be isolated in their homes for 21 days, stopping short of mandatory quarantines to fight the outbreak.

The U.S. Centers for Disease Control and Prevention created four risk categories and guidelines for how people should be monitored that are stricter than previous rules, said Tom Frieden, director of the CDC. The rules apply to health workers returning from fighting the outbreak in West Africa and for anyone in contact with Ebola patients in the U.S.

After a New York doctor was diagnosed with the Ebola virus last week, governors Andrew Cuomo of New York and Chris Christie of New Jersey announced policies requiring 21-day quarantines for anyone returning from a country with an Ebola outbreak who may have had contact with patients. The White House and infection control specialists have said those policies aren't based on science and will discourage aid workers from volunteering to fight the outbreak, which has infected about 10,000 people in Liberia, Guinea and Sierra Leone.