To do so, I would create a pivot table with dimensions e.g. department and organism name an add the # of organisms as an expression. Then by draging the department dimension to the top of the chart you can create one column per department each. The # of organisms then would be used to color code the background color (expression tab of the charts properties).
The result should look like this:
By sorting the organism and department dimensions using the # of organisms expression (descending) you can bring the most infectious of your organisms to the top of the table and the most involved departments to the left side.
This also allows for your users to focus on these specific departments and organisms: