The Texas hospital worker isolated on a Carnival Cruise ship after possible exposure to Ebola has tested negative for the disease. However, after the vessel returned Sunday to Galveston, Tex., an Oklahoma school district asked several employees and students who had been aboard not to return to school until she “has been ‘cleared’ and there is no medical threat.”

Moore School District, about 10 miles south of Oklahoma City, sent out automated calls and letters to parents, teachers and students, saying administrators “are in the process of identifying students who may have been on the cruise. Once identified, those students will also be required to stay out of school and will not be allowed to attend any school activities.” School officials said they hope to have the “all-clear” by Tuesday.

It’s in response to news that a lab technician at Texas Health Presbyterian Hospital may have come in contact with specimens from Liberian Thomas Eric Duncan, the first person diagnosed with Ebola in the U.S. The woman, who has not been named, did not have direct contact with Duncan, who died Oct. 8, but quarantined herself in a cabin aboard.

The woman and her partner boarded the ship, Carnival Magic, on Oct. 12 in Galveston before the Centers for Disease Control and Prevention updated the requirement for active monitoring, the U.S. State Department said Friday morning in a statement. At that time, CDC protocol called for “self-monitoring,” including daily temperature checks, which she was doing. After she left the country, health officials updated the monitoring protocol.

The woman was not allowed to leave the ship when it docked Thursday in Belize, nor would Belize allow her to be brought to shore for evacuation, according to a statement from the government. The boat was barred from port in Cozumel, Mexico, the next day, according to news reports. On Saturday, the  U.S. Coast Guard flew out to the vessel to retrieve a blood sample from the woman, Vicky Dey, vice president for guest services at Carnival, told Reuters. That sample tested negative.

When the ship docked Sunday morning in Galveston, officials boarded and conducted a final health screening on the hospital worker before she departed. State Department spokesman Jen Psaki said Friday it had been 19 days since the woman may have processed Duncan’s samples. Sunday would have been day 21, the final day of the incubation period.

“The Galveston County Health Authority has made the assessment that there is no evidence of a public health threat to cruise passengers or to Galveston County. The passenger and her travel partner have been allowed to disembark without restrictions,” county officials said in a statement.

The woman and her travel partner returned home on their own, according to a statement from Carnival Cruise Lines.

“No special cleaning requirements of the vessel have been requested by health authorities,” it said. “Nonetheless, to provide added assurance for our guests, we are undertaking a very comprehensive and aggressive cleaning and sanitizing initiative prior to guests boarding for the next voyage.”

Still, the Moore School District said it is “erring on the side of caution,” and at least some parents agree. One wrote on the school district’s Facebook page she is taking precautions of her own.

“On behalf of the parents of MPS students, we would like to know which schools have staff, faculty and/or students that are being told to not come to school following potential exposure to the Ebola virus whilst on board the Carnival cruise ship on October 17-18th?” she wrote. “Many parents, including myself, intend to keep our children (as a health precaution) home until we receive full disclosure, as aforementioned, preventing any individual decisions to not heed the advice of MPS to stay home.”