I have a population of patients who have received the same surgical procedure, but with one major difference in how the procedure was performed. I have monitored their infection rates for a period and I would like to know the most appropriate way to analyze the difference in these two groups. In particular I would like to be able to state whether there is a significant difference in the groups. The one group using the traditional surgical procedure is much larger than the non-traditional group. What is the most appropriate way to analyze the difference in their infection rates?

I suggest you read chaper 13 of Practical Statistics by John Neter, Third Edition.

It explains "Comparison of Two populations".