Nurith Aizenman

Ebola is on the rise in Sierra Leone's capital of Freetown. Just this week, 234 new confirmed infections were reported, and every day hundreds of residents call the emergency line to report more possible cases in their neighborhoods.

To deal with the surge, the nation sends health surveillance teams into the community to investigate the alerts, visiting up to five homes a day to check on residents.

The junior member of one team is Osman Sow, a young man with a wisp of a beard and a serious manner.

One reason the Ebola virus is so terrifying is that it's so lethal. Researchers estimate that the strain circulating in West Africa is killing upward of 70 percent of those it infects. Even among those getting care, as many as 64 percent are dying.

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