ATHENS, Greece -- Seven new cases of a mystery virus suspected of causing a potentially fatal heart inflammation were reported Wednesday. So far three people, all adults, have died from the infection.

Doctors urged Greeks to remain calm as the total reported cases of the ailment reached 39 since officials began counting on April 18. Most have been in Athens, the capital and home to nearly half of Greece's 11 million people.

All day-care centers, schools and universities remained closed around the country to prevent possible spread of the virus.