DALLAS — Several schools were closed and six airline crew members placed on leave Thursday following news a nurse with Ebola had taken a commercial flight, heightening anxiety over the spread of the virus and how authorities were handling the health emergency.

In Washington, federal health officials will be questioned by lawmakers at a congressional hearing into their response to the Ebola outbreak, a virus that has killed more than 4,400 people in West Africa and appeared on U.S. soil last month.

Dr. Thomas Frieden, director of the U.S. Centers for Disease Control in Atlanta, was scheduled to testify before a House of Representatives committee, a day after news emerged that a nurse who had treated an Ebola patient had flown from Ohio to Texas.

The nurse, Amber Vinson, 29, had a slight fever when she took the Frontier Airlines flight Monday, a day before she was diagnosed with Ebola. Frieden said Wednesday Vinson should not have flown, but a federal official later said she had contacted the CDC and was not prevented from boarding.

Frieden, who said last month he had “no doubt we will stop this in its tracks in the United States,” will likely face a grilling from members of Congress over how two U.S. health care workers became infected and one boarded a flight with 132 other passengers after being exposed to the virus.

At least one lawmaker has called for Frieden’s resignation and others, including House Speaker John Boehner of Ohio, urged travel restrictions on the countries hardest hit by Ebola.

Vinson was the second nurse at the Texas Health Presbyterian Hospital to become infected after exposure to Thomas Eric Duncan, the first person diagnosed with Ebola in the United States, who died on Oct. 8.

Another nurse, Nina Pham, 26, was diagnosed over the weekend and was being treated at the Dallas hospital, but the infections have raised concerns about how the facility handled the disease.

Rising public anxiety over the virus prompted President Barack Obama to cancel two days of political events just weeks before Nov. 4 congressional elections that will help shape the remainder of his term.

In Ohio, where Vinson had visited family members, two schools in the Cleveland suburb of Solon were closed Thursday because an employee may have traveled on the same plane as Vinson, though on a different flight.

The Ohio health department said the CDC was sending staff to help coordinate efforts to contain the spread of Ebola.

Frontier Airlines said it had placed six crew members on paid leave for 21 days “out of an abundance of caution.” Florida Governor Rick Scott asked the CDC to expand the reach of its contacts to people who flew on the same plane after nurse Amber Vinson’s flight. The plane made a stop in Fort Lauderdale after Dallas.

Back in Texas, the Belton school district in central Texas said three schools were closed Thursday because two students were on the same flight as a nurse infected with Ebola.