Incidence rates - best way to do trend analysis?

Hi everyone,

I have a series of admitted patient data and notifiable diseases data over a time period for 3 different study areas. For each year, I have calculated case counts by: overall, male overall, female overall, then each age grouping (<1, 1-4, 5-9,....85+), as well as each age group by gender (e.g., <1 male, <1 female, 1-4 male, 1-4 female, etc.).

Using the case count data, I used corresponding population data to then calculate incidence rates (per 100,000) for each of the same categories as listed above. So, my question is - WITHIN each study area I would like to test if there is a trend over time using the IRs. Then, once I do that, ACROSS each study area, I would like to test if there are differences in the trends between the 3 groups.

I'm not sure of the best way to go about doing this, so any help would be most appreciated! Thanks :D