A study is conducted at your hospital to learn about the relationship between HIV and intravenous (IV) drug usage. You identify patients from your emergency department who are IV drug users and those who are not and follow them for 1 year. During that year, you identify 69 new cases of HIV out of 253 who are IV drug users, and there are 17 new cases of HIV out of 450 who are not IV drug users. (The overall rate in both groups combined = 86 cases of HIV out of 703.) You are interested in developing an intervention to reduce the incidence of HIV and you would like to target a prevention program addressing risk factors. Create a 2 × 2 table using this information and answer the following questions.
• Calculate the incidence rate of HIV in the IV drug users (Iexp), in the non-IV drug users (Inonexp), and overall (I). Express all rates as “per 1,000.” • What type of study design is this? • Calculate the relative risk (RR) for this exposure. • Calculate the attributable risk (AR) for this exposure. Interpret this result. • Calculate the AR proportion for this exposure. Interpret this result. • What are some problems that may be associated with this kind of study design? • What are possible confounders?