Nurith Aizenman

The news is filled with stories of people in need. Perhaps they've just lived through an earthquake. Or they're war refugees. Or they're facing a deadly epidemic like Ebola.

Your heart goes out to them. And you're gratified that your government and other major donors are stepping in with a massive infusion of cash and other aid.

But how do we know if all that help is actually, well, helpful.

If you think the fight against Ebola is going well, here's a grim new number: 537.

That's how many new infections were reported in Sierra Leone in the past week. It's the highest weekly tally in any country since the West African outbreak began.

International governments and aid groups have scrambled to open Ebola treatment centers in the country. But, because of safety concerns, many of these centers are accepting only a fraction of the number of patients they were built to serve.

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.