The study will use social media to recruit a diverse sample of people who self-report injecting drugs, assessing the feasibility of online assessments and participants' ability to perform at-home self-administered HIV testing. Participants will complete online questionnaires at baseline and will be mailed HIV testing kits that they will self-administer and mail to a central laboratory. Investigators will track completion of questionnaires and whether at-home self-administered HIV tests were completed and sent to the laboratory.

In the past decade, injection drug use (IDU) has been linked to rural and urban HIV outbreaks, increased hepatitis C virus (HCV) transmission, and skyrocketing overdose rates in the US. Internet-based mail delivery public health programs mail naloxone or other HIV prevention supplies where allowed by law. Recruiting people who inject drugs (PWID) for research has traditionally been done in person, and the feasibility of collecting data from those who are recruited via the internet is unknown. Thus, the study's objectives are to: (1) recruit a representative sample of people who inject drugs for internet-based HIV prevention research; and (2) test the feasibility of at-home HIV testing for people who inject drugs.

This study will use social media to recruit 500 PWID. Investigators will assess the feasibility of online assessments and PWID's ability to perform at-home self-administered HIV testing. Participants will complete online questionnaires at baseline and investigators will mail participants HIV testing kits that they will self-administer and mail to a central laboratory. No other supplies will be mailed to participants.

1. Recruitment will occur through with study advertisements on social media platforms and websites (i.e., Reddit, Twitter, Facebook, Instagram).
2. Participants who click on an advertisement or study link will be taken to a screening questionnaire and informed consent page programmed into Qualtrics.
3. To help minimize potentially fraudulent participants, the program will use cookies to block multiple submissions from a given device. Study staff will also manually review all surveys flagged for suspicious responses using a pre- determined process, such as comparing responses from the same Internet Protocol (IP) addresses, and examining those from proxy-IP addresses.
4. Participants who complete informed consent and the baseline questionnaire will provide an e-mail address (to receive compensation) and a physical address where an HIV testing kit could be mailed.
5. The research team will mail participants an OraSure HIV-1 Oral Specimen Collection Device. A self-addressed and stamped envelope will be included with the collection kit. Participants will follow enclosed directions to collect oral-fluid samples and mail them to the study laboratory for analysis. Envelopes and samples will only be marked with a bar code and not with any other personal identifiers (e.g., name or address).
6. Research staff will follow a defined protocol to deliver any positive HIV tests results.

Inclusion Criteria:

• 18 years or older
• US residency
• English or Spanish fluency
• injection drug use (self-report, past 30 days)
• basic reading comprehension

Exclusion Criteria:

• HIV status known to be positive

Data collected on injection drug use could include self-disclosure of illegal activity. Participant information will be kept confidential to protect privacy.