US health authorities are expanding the number of airline passengers they want to speak with after a nurse flew from Texas to Ohio days before being diagnosed with Ebola.

The extra outreach extends to people who flew on the same plane during five different trips, and to people who traveled on the nurse’s initial flight from Texas to Ohio on October 10, airline and government officials said.

Frontier Airlines said it has emailed “approximately 750 additional passengers via email asking if they have concerns,” the company said in a statement late Thursday.

“If they have any concerns, they should contact their local health authorities,” it said.

The additional passengers “include those aboard the five flights on the same plane that Nurse 2 flew on October 13” from Cleveland, Ohio to Dallas, Texas.

Meanwhile, the US Centers for Disease Control said it was expanding the net of potential contacts to those who flew on the nurse’s initial journey from her home in Dallas to visit relatives in Cleveland on October 10.

That flight took place five days before the nurse, Amber Vinson, tested positive for Ebola on October 15. Previously, the CDC had said it was contacting passengers on her October 13 flight only.

– ‘Additional information’ emerges –

The CDC said it expanded the outreach “based on additional information obtained during interviews of close contacts” of the nurse, but gave no further details.

Vinson had reported a low-grade fever of 99.5 Fahrenheit (37.5 Celsius) to the CDC on October 13 and was cleared to fly.

The threshold that would have kept her from flying was 100.4 F (38 C).

Vinson’s colleague, nurse Nina Pham, was diagnosed with Ebola on October 12.

Both worked in the intensive care unit of Texas Health Presbyterian Hospital Dallas and cared for a Liberian man who died of Ebola on October 8.

CDC chief Tom Frieden has said Vinson “reported no symptoms to us,” on October 13 but that she should not have been allowed to board a commercial airline.

After Pham’s diagnosis, Vinson was moved into a higher risk group of around 70 healthcare workers who had contact with the Liberian patient, Thomas Eric Duncan, or his blood specimens. People in this category are not supposed to take public transport.

Passengers on Frontier Airlines flight 1142 Dallas/Fort Worth to Cleveland on October 10 and passengers on Frontier Airlines flight 1143 from Cleveland to Dallas/Fort Worth on October 13 are asked to call 1 800-CDC INFO (1 800 232-4636).

“Public health professionals will interview passengers about the flight, answer their questions, and arrange follow up if warranted,” the CDC said in a statement.

“Individuals who are determined to be at any potential risk will be actively monitored.”

Officials have stressed that the risk of infection is extremely low, since Vinson was not vomiting or having diarrhea on the flight.

Ebola is spread through close contact with the bodily fluids of an infected and symptomatic person — through broken skin or mucous membranes in the eyes, nose, or mouth — and has an incubation period of two to 21 days.

Vinson first reported symptoms to the CDC on October 14, a day after her flight from Ohio to Texas.

“Ebola is killed with hospital-grade disinfectants (such as household bleach),” the CDC statement added.

“The airline used appropriate measures to thoroughly clean the plane consistent with our guidelines.”