There's a new survey of businesses in Burundi that has just become available from the World Bank Enterprise Surveys. It was undertaken in 2014-2015 and is available here. From a viewpoint of understanding what makes companies successful or challenges them, the Enterprise Surveys are a great resource.
I have been using the 2006 survey, so a more recent one is going to be informative. Looking at the data variables, it looks like there is new information on sources of revenue, and on innovation. I haven't checked yet whether the data is from all over the nation, which would be welcome. The 2006 survey only had data from Bujumbura.