Actually 21 days is the longest incubation period. Some people get sick in as little as 2 days. Average is about 10 to 12 days with over 90% getting sick sighing 15 to 16 days IIRC. Someone posted a chart showing this.
As you said correctly, though, you can’t be sure for 21 days. Although if the deputy is symptomatic, tests can confirm whether or not his symptoms are from Ebola. We should know with respect to him later today.
PS I’m doing this from memory so please forgive if I am off a day or two, but that’s the general gist.
According to this news report in the link at the top,
“Ebola test results are due back Friday evening”
Anyhow, it was a week ago he grabbed Duncan. I would say if the Deputy has nothing in 3 weeks, then he will be in the clear.