FREETOWN, Sierra Leone - Another Sierra Leonean doctor has become infected with Ebola, as the UN health agency said Wednesday that poor data from the outbreak is complicating efforts to measure progress in containing the disease.

Ebola has sickened more than 17,000 people, the majority of those in Guinea, Liberia and Sierra Leone. The disease has exacted a particularly heavy toll on health workers and another tested positive on Tuesday in Sierra Leone. Dr. Dauda Koroma is being treated at a military hospital in the capital, according to Chief Medical Officer Dr. Brima Kargbo.

While the disease is still spreading rapidly in Sierra Leone, health officials have expressed some optimism that the outbreak is stabilizing in Guinea and Liberia. The World Health Organization said Monday that those two countries had met an interim goal to isolate 70 percent of patients and safely bury 70 percent of corpses.

But in a report Wednesday, WHO called into question that progress, saying the data is too poor to draw conclusions.

Inconsistencies in data collection mean "this information is not reliable enough at present to draw any conclusions about isolation," the report said. It added that getting information on safe burials was complicated by the fact that many Ebola deaths go unreported.

In Sierra Leone, unsafe burials are thought to be responsible for 70 percent of new infections, Kargbo told reporters Wednesday.

The WHO report said there are enough isolation beds in each country to handle the reported cases - but often not in the places they're needed. Clinics are fairly well distributed in Liberia, the report said, but less so in Guinea. And Sierra Leone needs many more beds in its capital region.

The nation is also short on health care workers. About 100 more African health care workers are expected soon, said Kargbo.

The African Union has promised to send 1,000 health care workers to the three affected countries by the end of the year, but they have been slow to deploy. So far, 87 have arrived, but the AU held a send-off ceremony for 250 more from Nigeria on Wednesday.