(Bill O’Leary/The Washington Post)

Updated at 10:27 p.m.

Despite progress fighting Ebola in Liberia, a surge in the number of cases and a shortage of treatment beds in neighboring Sierra Leone and Guinea pose “sobering” challenges to stopping the epidemic in West Africa, the head of the Centers for Disease Control and Prevention said Monday.

CDC Director Thomas Frieden said the conditions he saw on a week-long trip to the three hardest-hit countries were “a world of difference” from his visit in late August and September, when the number of cases was increasing exponentially in Liberia and dead bodies lay in streets and in treatment centers.

This time, there is “real momentum,” he said. “I’m hopeful about stopping the epidemic, but I remain realistic that this is going to be a long, hard fight.”

In some parts of the region, health-care workers are becoming less vigilant about wearing protective equipment, he said. One nurse he spoke with at a hospital in Conakry started an intravenous line in a patient from Sierra Leone without putting on gloves. “The nurse ended up getting Ebola and surviving and is now dealing with the stigma at home and at work,” he said.

In a telebriefing, Frieden said he couldn’t predict how long it would take to bring the caseload to zero. This next phase will require responders to “double down” on labor-intensive disease detection to track down every single case, identify contacts and isolate and treat the sick, he said.

The three countries now have 19,340 cases, including 7,558 deaths, and the number of cases in Sierra Leone is now larger than  it is in Liberia, according to the latest data from the World Health Organization. When Frieden held a news conference Sept. 2 after his first visit to the region, the virus had infected more than 3,000 people and killed more than 1,500 of them.

Liberia “has the upper hand against the virus,” he said. But in parts of Monrovia, disease detectives are having trouble tracking down cases because some patients are heading to Ebola treatment units hours outside the city. One family, believing that treatment outside the capital was safer, took a six-hour taxi ride to an ETU, potentially exposing the taxi driver and others, he said.

In Sierra Leone, the challenges “remain very extensive,” with at least 10 confirmed deaths a day from Ebola, he said. Fear of Ebola has also scared pregnant women and others with malaria and pneumonia from seeking treatment at hospitals. But Frieden said that if the global response remains strong, Freetown and the western parts of the country “should see a significant decrease in cases” within the next few weeks.

In Guinea, Frieden traveled to the remote area that was the epicenter of the outbreak a year ago and was encouraged to see an Ebola treatment unit and a decrease in the caseload. But in the capital of Conakry, “one of the scariest things I heard” came from a Doctors Without Borders team leader, who told Frieden that for the first time since the outbreak, they recently had more patients than isolation beds.

As a sign of progress, Frieden cited one rural town in Liberia where nearly 100 people have died. A grave-digging team there now has so little work that it is making furniture for families of survivors.

Frieden said the CDC will devote even more resources and staff to the effort. It will establish offices in each of the three countries and work closely with partner organizations, including the World Health Organization, the African Union and non-governmental organizations.

Related: Inside the CDC’s fight against Ebola