Texas Health Presbyterian Hospital in Dallas. (Mike Stone/Reuters)

The emergency operations office at the Centers for Disease Control and Prevention in Atlanta was very quiet. It was late in the afternoon on Tuesday, and a dozen or more CDC staff had gathered to hear the latest news out of Dallas about the suspected Ebola patient, Thomas Eric Duncan.

David Kuhar, an infection control medical officer at the CDC, was listening in.

He knew he might be flying out sooner rather than later, which is why he drove to work that day instead of riding his bike, as he usually did. On the conference call were local and state health officials from Texas.

And they had news about Duncan’s lab results:

“It’s positive for Ebola.”

Those were the words everyone at the CDC dreaded, but in truth expected.

And with that, some of the world’s premiere health investigators took off, with Kuhar, a specialist in contagious infections, in the lead.

He was an expert in Ebola and had been to Africa and was called in for the outbreak of Middle East Respiratory Syndrome (MERS) in 2012 on the Arabian Peninsula. That dangerous infection has now spread globally, including to the United States.

Ebola in the United States was always a possibility -- perhaps an inevitable one, the CDC team knew. Now they had their own patient zero.

Before the conference call ended, Kuhar was already headed out the door. Within minutes, the CDC had made his travel arrangements. Booked on the 9:50 flight to Dallas, he dashed home to pack. An hour later, he was parking his 2002 Honda Accord in the economy lot (he knew he wasn’t coming home anytime soon) and hoofed it to the main terminal.

At least seven of the eventual 10 members of the team made the flight. (The number of CDC staff in Dallas will fluctuate over the coming days and weeks, Kuhar said, but the group includes senior epidemiologists, epidemic intelligence officers, doctors and nurses.)

Everyone on the team dropped what they were doing. One member based in Houston immediately got in his car and drove to Dallas. Communications coordinator, Dave Daigle, quickly cancelled vacation plans with his wife and his plans to visit his mother in Florida.

By the time the team arrived at the Courtyard Marriott on the North Central Expressway in Dallas, it was past midnight.

Less than 24 hours after the Ebola confirmation, the team was in place, just a mile from Texas Health Presbyterian Hospital. The Marriott would be their unofficial headquarters for the time being.

Kuhar was up at 6:30 the next morning, Oct. 1, a Wednesday. The team met briefly in the lobby, inhaling oatmeal, fruit cups and coffee. At 7:30, they were at the hospital. By 8, they were in a conference room with dozens of county and state health officials for what Kuhar called “a meet-and-greet.”

“We’re here to assist you,” he told the anxious crowd. “Our immediate priority is contact tracing – contact with people who might be at risk of becoming sick.”

The doctor spoke for nearly an hour. Low-key and soft-spoken, Kuhar has a naturally calm disposition. At the end, he took questions. Few were asked. He wasn’t really surprised.

He understood it was all so new, so confusing for these people, but he made it clear there was a plan in place and a protocol to deal with those who had been exposed.

Before the CDC team could even begin, though, they had to split up. “Divide and conquer,” Kuhar called it. Some of the investigators would do the contract tracing at the hospital, which Duncan visited before Ebola was even suspected, and the others had the harder job: Tracing Duncan’s path in the community at large.

For the next 12 or so hours, half the CDC investigators stayed at the hospital pouring over a “line list,” the people known to have had contact with Duncan, specifically from the time his first symptoms appeared, which Kuhar said is the “beginning of the period of risk of transmission.”

“We needed to meet with (Duncan’s) family first,” he added.

The team solicited the local health department for assistance in developing a line list for the community. Between the two lists, there were roughly 100 names of people who may have had contact with Duncan. Team members worked phones and drove around Dallas for person-to-person interviews. The hospital had already worked up a list, so it was easier reaching those on staff.

By midday Thursday, 48 hours after notification of Duncan’s positive Ebola test, the CDC investigators in Dallas had interviewed the entire line list. Now, they would fan out with local and state health officials to begin daily monitoring of symptoms of those they knew had direct contact.

By 5 p.m. that evening, officials had already made a second visit to the home of Youngor Jallah and Aaron Yah and their four children. All had been in contact with Duncan at the home of his girlfriend, Louise Troh, when he was taken by ambulance from the Ivy Apartments to the hospital.

All six – Louise Troh is Jallah’s mother – were at high risk. But as of Thursday evening, all were still asymptomatic and had no fever.

Refining the list into high-risk vs. low-risk was the next major task for the team. Obviously, those at the highest risk needed to be observed closely over the coming days and weeks. The list would shrink, but the danger to those at highest risk would not, at least for the time being.

“Everyone who worked in the ER that night, all the way down, were at risk,” Kuhar said. “You cast as wide a net as possible and then you just whittle down, whittle down.”

Read more: Quarantined relatives of U.S. Ebola patient speak out