U.S. Ebola case: Thomas Duncan visited Liberia to see his girlfriend + had contact with 20 people .

America's first diagnosed Ebola victim is contained, but three things are still spreading: fear, frustration and the search for his contacts.

While Thomas Eric Duncan remains in critical condition at a Dallas hospital, some parents are scared to take their kids to the school that his girlfriend's children attended.

Others are upset at the hospital where Duncan first sought care, which sent him home and raised the possibility he could infect others for at least two additional days.

As the search continues for those Duncan had contact with, here's the latest on how the case is affecting others:

'I just got scared'

Duncan was in Dallas visiting his girlfriend, Liberian community leader Stanley Gaye said.

Among the people he came in contact with, Gaye said: his girlfriend's five children.

Dallas Independent School District Superintendent Mike Miles said the patient came in contact with five students who attended four different schools in the area.

Sam Tasby Middle School is one of those schools.

"I just got scared because I thought that that kid came to that school and probably got contact with him," said Nellie Catalan, whose child attends the school.

"I know it doesn't get (spread) by the air, but you never know."

More than 3,500 students attend the four schools. Each is getting cleaned and sanitized over the next few days.

Student Denise Trujillo said she's still worried.

"I don't feel like going to school tomorrow," she said.

While the five students who were near Duncan are staying home and being monitored, their schools will remain open.

'They dropped the ball'

Four days after he arrived in Dallas from Liberia, Duncan started feeling symptoms on September 24. That day is significant because that's when he started being contagious.

Late the following night, he went to Texas Health Presbyterian Hospital Dallas with a low-grade fever and abdominal pain, the hospital said.

Duncan actually told a nurse he had been in Africa.

But "regretfully, that information was not fully communicated throughout the full team," said Dr. Mark Lester, executive vice president of Texas Health Resources.

Duncan was sent home with pain killers and antibiotics -- only to return in worse condition on September 28. That's when he was isolated.

"It was a mistake. They dropped the ball," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said of the miscommunication at the hospital.

""You don't want to pile on them, but hopefully this will never happen again. ... The CDC has been vigorously emphasizing the need for a travel history."

Gupta said this mishap doesn't make sense.

"A nurse did ask the question and he did respond that he was in Liberia and that wasn't transmitted to people who were in charge of his care," CNN Chief Medical Correspondent Sanjay Gupta said. "There's no excuse for this."

And one of Duncan's friends said he was the one contacted the CDC with concerns that the hospital wasn't moving quickly enough after Duncan's second hospital visit.

But the hospital said the patient's "did not warrant admission' last week.

'It gets bad -- fast'

In the roughly four days he was contagious and not isolated, Duncan came in contact with up to 20 people, Dallas Mayor Mike Rawlings said.

Those contacts will be monitored for 21 days -- the longest amount of time it takes for Ebola symptoms to show up.

The three-week long monitoring is important because the early symptoms of Ebola can include ailments that could be confused with a common illness: abdominal pain, fever and vomiting.

But "Ebola tends to progress much more quickly," Gupta said. "It gets bad -- fast."

So far, so good.

Members of the ambulance crew that transported Duncan to the hospital haven't shown symptoms, Rawlings said.

Neither have his girlfriend's children.

"They are doing well. ... They are doing fine," Gaye, the Liberian community leader.. "All she asks for are our prayers."

But if one of those contacts ends up having Ebola, the tedious processes of tracking and monitoring a web of contacts would have to start all over again.