I have a dataset and I am trying to model rates of infection over 5 years.


The dataset is similar to this one below with data going up to December 2015
month and year (yearmo) number of infections caused by organism x
(infx)		 total number of infections
(inftot)
jan 2010 54 664
feb 2010 44 566
........etc etc
december 2015 114 894

I am trying to model this count data using a Poisson regression to get the rates of infection caused by organism x over the 5 years. As the number of infections reported varies from each year, I have used the offset command to take this into account which requires me to log the number of total infections. I have therefore logged the total number of infections to make a variable called loginftot for my below regression.

My current code looks like this:
HTML Code:
poisson infx yearmo, irr offset(loginftot)
My questions are the following and would really appreciate if anyone could help answer them:
1) The resulting incidence rate ratio will be the change in rate of infection caused by organism x per month. Am I correct in interpreting this? For example, if my rate ratio is 0.98, does that mean that the number of infections per month caused by organism decrease by a factor of 0.98?

2) I was kindly wondering whether this was the correct use of the offset command. As previously mentioned, I use the offset command to account for the fact that different numbers of infections are reported per year.

3)I was finally wondering whether this coding was correct in Stata?

Thanks for your help in advance!