ATLANTA – Public health officials on Monday sought to assure Americans that the blood supply was safe despite concerns that an organ donor who received a transfusion may have transmitted the disease to four transplant recipients.

One of the four died of brain swelling that can be caused by the virus, which until now has been blamed solely on mosquito bites.

The three others were hospitalized with symptoms associated with West Nile, although doctors aren’t sure they have the virus or whether they got it from a medical procedure.

The organ donor, a Georgia woman, died in a car crash last month. She may already have been infected or may have gotten West Nile through blood transfusions in the emergency room after the crash, the CDC said.

Samples from the four transplant recipients were sent to the CDC’s lab in Fort Collins, Colo. Test results are expected within the week. The organ recipient who died was in the Atlanta area. The others are in undisclosed hospitals in the Atlanta area, in Miami and Jacksonville, Fla., health officials said.

Public health officials spent the weekend assuring people about the national blood supply, despite the lack of a West Nile screening process in donated blood and organs. Any potential blood donor showing symptoms of the virus would be turned away, they said.

“The blood supply is as safe as it’s ever been,” Trudy Sullivan, an American Red Cross spokeswoman in Washington, said Monday.

The Food and Drug Administration issued an alert to blood banks two weeks ago to exercise extra caution when screening donors.

“We’ve known for some time that there is a theoretical possibility that people can get this through blood or organ transplants,” said Tom Skinner, a Centers for Disease Control and Prevention spokesman, said Sunday.

So far this year, 638 people in 27 states and the District of Columbia have tested positive for West Nile virus, and 31 have died.

At blood donation centers, officials said people weren’t panicky about West Nile and transfusions.

At the Aventis Plasma Center, a blood bank in Tallahassee, Fla., a manager said West Nile hasn’t even come up in clients’ questions.

“Not even mentioned,” manager Gwen Jones said, “not once.”At Atlanta’s Centennial Olympic Park, where dozens of parents spent the holiday watching their children with sunblock in one hand and bug spray in the other, word of a new West Nile risk didn’t go over well.

“It was prevalent before, and now we hear it’s more prevalent,” sighed Clinton Orlando of Atlanta.

He said if he needed a transfusion, he wouldn’t refuse it. “But I’d probably be very choosy about where I’m being treated and ask a whole bunch of questions about the blood and where it came from. It seems like there’s a lot of guesswork involved,” he said.

In Chicago, Patty Harty said blood should be screened more carefully for the virus. She said her 8-month-old twins and her 3-year-old son do not go out after dark as a precaution.

“This whole issue with the transplants is scary. I do feel that they should try and test it a little bit better,” she said. “It’s a scary time.”