Probability of catching an STD

Hi everyone.

I'm trying to figure out the likelihood of someone catching an STD based on data posted on the CDC website. The data is broken down by disease, state, gender, ethnicity, age group, # of cases, total population, and incidence rate.

As an example, suppose the total female population of 20-24 year olds from a certain ethnic group is 12,188, and of those, there are 43 reported to have an STD. The incidence rate is 325.81 (the CDC uses 100,000 as a factor in calculating this). If a male were to sleep with a female from that group, what's the likelihood of him catching something? Does the incidence rate for the overall male population matter in this case, for say, calculating the relative risk factor?

For those interested in the data, you can find a generator here: http://wonder.cdc.gov/std-std-v2008-race-age.html . Choose "Disease", "State", "Gender", "Race/Ethnicity", "Age" and press "Send" to replicate the conditions I listed above.

Thanks in advance.