Calculating Absolute rate reductions with Count Data

Hello everyone,
I'm analyzing count data in stata using negative binomial regression because of overdispersion. I'm reporting incident rate ratios using the model I've described below. Is there also a way to calculate an absolute rate reduction based on the level of exposure? This study is policy related, so I think reporting the absolute rate reduction would be of additional benefit.

Exposure: 4 level categorial variable
Outcome: Injury count
Covariables: several continuous variables
Offset: log of the population at risk
Clustered at the state level b/c of correlated data.

Thanks for any advice you can offer.