What we know about the spread of Ebola amid growing outbreak in DRC

At least 363 cases and 62 deaths have been confirmed in the DRC.

A deadly Ebola outbreak is continuing to spread across the Democratic Republic of the Congo, with global health officials warning that "we are still behind."

As of Wednesday, 363 cases of Ebola and 62 deaths have been confirmed, according to the Congo Ministry of Health and the Centers for Disease Control and Prevention (CDC). In neighboring Uganda, 15 cases and one death have been confirmed, health officials said.

The latest DRC Ebola situation report shows the outbreak has now reached Mambasa, a new health zone located more than 160 kilometers south of the mining town of Mongbwaluin in Ituri province, where cases have been concentrated. This suggests the virus is continuing to spread geographically.

"The outbreak had a big head start and we are still behind ... but we're catching up," Dr. Tedros Adhanom Ghebreyesus, the director-general of the World Health Organization, said during a press briefing on Wednesday.

Recently, the WHO ruled out hundreds of suspected cases after investigation. Although some local health officials suggested that community transmission may be slowing, many public health specialists cautioned that data is very incomplete. The specialists also noted that contact tracing is weak and far below the level needed to contain the outbreak.

However, the specialists acknowledge that the public health response is ramping up and that health authorities are getting a better sense of how many confirmed cases there are.

Dr. Megan Coffee, an infectious disease physician and a senior specialist in infectious diseases in health unit of the aid organization International Rescue Committee (IRC) highlighted the importance of clarifying certain details as they try to control the outbreak.

"To be able to say what is the case fatality, what is the percentage of cases that have been identified, and what have been the percentage of people who are potentially in a chain of transmission may been exposed and may develop Ebola," she told ABC News.

On Tuesday, the WHO said there were 116 suspected cases, with hundreds of suspected cases ruled out after investigation.

That came after the global health agency said on Friday that 906 suspected cases were under investigation. However, in an op-ed by published in the Financial Times on Sunday, the director-general of the Africa Centres for Disease Control and Prevention, ​wrote that there were more than 1,100 suspected cases.

When asked about the massive drop, WHO spokesperson Christian Lindmeier told reporters at the agency's headquarters in Geneva that hundreds of cases "have been cleared out and have either other diseases or have just had fever and nothing else," according to Reuters .

Lindmeier added that the numbers will shift as more people get tested, a statement Coffee agreed with.

"Those numbers will change a bit because suspected cases can be ruled in or out," Coffee said. "And new people can be identified; new suspects can be identified at any point. So, these are numbers that are always changing."

Brittany Kmush, an associate professor of public health at Syracuse's Maxwell Schoo of Citizenship and Public Affairs who specializes in infectious disease epidemiology and outbreak surveillance, told ABC News it's important to keep in mind that the incubation period -- the time between exposure to a pathogen and the first appearance of symptoms -- for Ebola is up to 21 days.

She said it has not even been 21 days since the WHO declared the outbreak to be a public health emergency of international concern, so "the trajectory of this epidemic" remains unclear.

"People who were exposed on May 17 may not even be sick yet," she said. "And then there's the size of the epidemic when it was recognized ... and so that means there was a lot of undetected circulation, which means there's a lot of cases that we don't know about and contacts that we know about."

One of the biggest issues facing the response effort is contact tracing, which involves identifying anyone exposed to infected individuals so they can seek medical care, testing or quarantine.

About 44% of contacts are being traced in Ituri, the main affected province in the northeastern DRC. WHO chief Tedros said on Wednesday that this figure needs to increase to about 90%.

Coffee said identifying every contact is difficult in an area where some people may not trust the authorities and others are in denial about Ebola being a real virus or being infected themselves.

Additionally, she said it can be hard to travel between areas, especially in more rural or remote regions, to identify cases and contacts.

"It's very, very hard early in an outbreak to know that you have all the chains of transmission," Coffee said. "There will often be chains of transmissions in a larger outbreak that you just haven't noticed."

Kmush added that there's a lot of stigma around Ebola and people may be worried about reporting all their contacts to health authorities.

"It's going to be very difficult to get all the contacts identified and followed properly, especially since the international aid community is really short on resources," she said. "You don't want to be short on people and resources to do the contact tracing, short on places to go for people to quarantine and isolate."

Coffee added that that one of the Ebola hotspots in the DRC is an area with a gold mine and many migrant workers, which has complicated the ability to track cases.

"When you do contact tracing, it's a lot easier when everyone has a fixed address; they've lived in that address their entire life, and all of their neighbors know them," she said. "When you have populations that are on the move, you'll have more of a difficulty in tracking down like. 'You know how to contact Henry who was here a week ago, right?'"

ABC News' Dragana Jovanovic contributed to this report.

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