Participants will receive the on-site bundled rapid HIV/HCV testing intervention. In the intervention group, all patients will receive an offer to participate in rapid HIV/HCV testing. Those who accept this offer will: receive pre-test information about testing procedures and education, be tested, receive results during the same visit as testing, and be provided post-test counseling and support services by trained test counselors. Patients with a preliminary positive (i.e., reactive) HIV and/or HCV test result(s) will be actively linked immediately to a health care provider for further evaluation and confirmatory HIV and/or HCV RNA testing.

Participants will receive the standard of care (SOC) at the study sites. The SOC entails venipuncture whole blood HIV testing + venipuncture whole blood HCV testing. Blood draws are sent to an external laboratory for processing, and patients must return for test results in another visit. Patients may not receive pre-test information or results and post-test counseling, especially if non-reactive or negative test result(s). Reflex testing is not standard practice, therefore some patients may require another visit and blood draw for confirmatory HIV and/or HCV RNA testing. Linkage to care in the SOC is accomplished by referral to a health care provider, either within the participating substance use disorder treatment organization or passive referral to other health facilities.

Participants will be offered bundled on-site rapid HIV and HCV testing with post-test counseling that addresses both sexual and drug use risk reduction, and linkage to care.

The primary outcome is self-reported receipt of HIV/HCV test results. This will be measured at one-month post-randomization for all participants. We acknowledge that there are several potential HIV/HCV testing behaviors that could be evaluated in this study: acceptance of testing, completion of testing, and receipt of testing results, either HIV or HCV. Acceptance of testing measures whether or not a participant would accept the offer of an HIV or HCV test. Completion of testing measures whether or not a participant completes the HIV or HCV test. Receipt of test results refers to whether or not a participant self-reports having received the results of the HIV or HCV test.

Proportion of patients who initiated HIV/HCV care before the 3-month follow-up among those whose test results were positive for HIV and/or HCV.