The Democratic Republic of Congo's Ebola outbreak hit 500 cases this week, according to an Dec. 11 update from the Center for Infectious Disease Research and Policy at Minneapolis-based University of Minnesota.
Here are three things to know:
1. Of these cases, 452 are confirmed and 48 are suspected. The outbreak has also caused 289 deaths, 241 of which are confirmed. Congo health officials said they are investigating another 80 people for suspected infections.
2. Health officials are still having trouble identifying transmission chains in Congo. Of five new Ebola cases identified Dec. 8, only two occurred in known contacts of other Ebola patients.
"Particular challenges lie in investigating new confirmed cases without clear epidemiological links to other cases," the WHO regional office said in a Dec. 11 update, adding that contact tracing still proves difficult due to insecurity and continued community resistance.
3. As of Dec. 11, health workers have vaccinated 44,447 people with Merck's experimental Ebola vaccine. The WHO said it has 4,290 doses left in its stockpile for the city of Beni, which has been the outbreak's epicenter. About 30 percent of the 119 cases confirmed between Nov. 18 and Dec. 8 occurred in Beni.