So I noticed you've only just joined 7Sage. Welcome! So, howlong have you been studying since before 7Sage? It's only like 5 or 6 weeks until December. If you've just started studying, it would be better to forego December all together.
... month howlong an individual had virus" translates to "to estimate howlong an ... to estimate within a month howlong that person has had ... that the accuracy of determining howlong a person has had ... but the accuracy of estimating howlong the person has had the ...