Similar to the previous year’s recruitment process, AMIS participants were recruited through convenience sampling from a variety of websites using banner advertisements or email blasts to members of the website (hereafter referred to generically as ads). For AMIS 2018, data were collected from September 2018 to December 2018. The survey was not incentivized. Men who clicked on the ads were taken directly to the survey website hosted on a secure server administered by SurveyGizmo. Recruitment was also done by emailing participants from the previous cycle of AMIS (AMIS 2017) who consented to be recontacted for future studies. To be eligible for the survey, participants had to be aged ≥15 years, be cisgender male, reside in the United States, and report that they either had oral or anal sex with a male partner at least once in the past or identify as gay or bisexual (hereafter referred to as MSM). Persons who were aged <15 years or refused to provide their age were not asked any other screening questions. MSM who met the eligibility criteria and consented to participate in the study started the web-based survey immediately. The full questionnaire for AMIS 2018 is presented in Multimedia Appendix 1.

Several data cleaning steps were performed on the raw data set of eligible responses to obtain the final analysis data set, in the same manner as in previous AMIS cycles [2-6]. Briefly, these steps were as follows: deduplication; limiting to surveys deemed successful, that is, observations with no missing values for the first question of at least two consecutive sections; limiting to participants who reported having oral or anal sex with a male partner in the past 12 months; and ZIP code validation. These steps are further described in detail.

First, to deduplicate survey responses, demographic data for near-complete (>70%) survey responses with nonunique internet protocol addresses were compared, and responses that showed a 100% match for age, race, ethnicity, ever having sex with a woman, and email address were considered to be duplicate responses. Only the observation with the highest survey completion was retained. The data set was, then, limited to those surveys that were deemed successful. Finally, the data set was restricted to include participants who reported having oral or anal sex in the past 12 months and who provided a valid US ZIP code. ZIP codes were validated in the same manner as done in AMIS 2017 [6]. Valid US ZIP codes were those that could be matched to the ZIP code of county crosswalk files created by the US Department of Housing and Urban Development [8]. Any ZIP codes that could not be matched to this list were then hand validated by checking against the ZIP code locator tool on the US Postal Service website [9]. ZIP codes that could not be found were classified as invalid.

The study was conducted in compliance with federal regulations governing the protection of human subjects and was reviewed and approved by our institution’s human subjects research review board. No incentive was provided to the participants. Data sets for analyses were stored on secure data servers with access only granted to study staff. The study data are protected under a federal certificate of confidentiality that prevents legal action to force data release.

For the AMIS 2018 analyses, participants were categorized as either AMIS 2017 participants who took the survey again or new participants from the website or app based on the target audience and purpose: gay social networking (n=2), gay general interest (n=1), general social networking (n=4), and geospatial social networking (n=2). Recruitment outcomes and demographic characteristics for the AMIS 2018 participants are presented in the first two tables, and thereafter, they are recategorized to how they were originally recruited in AMIS 2017. We did not provide the names of the websites or apps to preserve operator and client privacy, particularly when a category has only one operator. Participants whose data were eligible, unduplicated, and successful and who provided consent; reported having male-male sex in the past 12 months; and provided a valid US ZIP code were included in analyses of participant characteristics and behavior.

To facilitate comparisons, the key indicators and analytic approach used in AMIS were designed to mirror those used by the NHBS system [10]. Population density was defined in the same manner as defined in AMIS 2017 and was based on the National Center for Health Statistics Rural-Urban classification scheme for counties [11]. The self-reported HIV status was categorized as HIV-positive, HIV-negative, or unknown, consistent with surveillance reports produced by the NHBS system [10]. In total, 3 substance use behaviors in the past 12 months were assessed: use of nonprescribed marijuana, use of methamphetamines, and use of any illicit drug other than marijuana or methamphetamines. All other indicators assessed remained unchanged from AMIS 2017 [6].

The analysis methods for AMIS 2018 did not substantively differ from those previously published but are repeated in this report for clarity. Overall, chi-square tests were used to identify whether participant characteristics differed significantly among recruitment sources. Multivariable logistic regression modeling was used to determine significant differences in behaviors based on the self-reported HIV status while controlling for race or ethnicity, age group, NHBS city residency, and type of recruitment website. The metropolitan statistical areas included in the NHBS system in 2018 were as follows: Atlanta, Georgia; Boston, Massachusetts; Chicago, Illinois; Dallas, Texas; Denver, Colorado; Detroit, Michigan; Houston, Texas; Los Angeles, California; Memphis, Tennessee; Miami, Florida; Nassau-Suffolk, New York; New Orleans, Louisiana, New York City, New York; Newark, New Jersey; Philadelphia, Philadelphia; Portland, Oregon; San Diego, California; San Francisco, California; San Juan, Puerto Rico; Seattle, Washington; Virginia Beach-Norfolk, Virginia; and Washington, District of Columbia. HIV testing behaviors were only examined among those who did not report that they were living with HIV, and these data were presented in participant characteristics. The multivariable logistic regression results were presented as adjusted odds ratios (aORs) with 95% CI and Wald chi-square P values to denote an independently significant difference in the behavior for each subgroup compared with a reference group. Statistical significance was set at P=.05.

AMIS 2018 was conducted from September 2018 to December 2018 and resulted in 91,142 persons screened for eligibility (Table 1). Of the 3713 participants who completed the AMIS 2017 survey and were emailed links to the AMIS 2018 survey, 39.94% (1483/3713) completed the screening. Almost half (42,011/91,142, 46.09%) of the participants who completed the screening process were eligible to participate. The most common reason for ineligibility was not ever having male-male sex or not identifying as gay or bisexual. Almost all (40,847/42,011, 97.23%) of the participants who were eligible consented to participate in the survey. A total of 6595 (6595/40,847, 16.15%) surveys were likely from duplicate participants. Among unduplicated surveys, 35.75% (12,246/34,252) were considered successful. Most successful surveys were from men who reported having sex with another male in the past 12 months (10,232 /12,246, 83.55%). Almost all of these surveys (10,129/10,232, 98.99%) provided a valid US ZIP code. Overall, the completion rate was 11.1%, with an analytical sample consisting of 10,129 surveys from 91,142 screened participants. The median survey completion time, including eligibility screening, was 20.7 minutes (IQR=16.5-27.4).

In total, 69.22% (7011/10,129) of the participants included in this report were non-Hispanic White and 41.76% (4230/10,129) were aged 15-24 years; the most common region of residence was the south, followed by the west (Table 2). Participants were recruited from all US states, and there were at least 100 participants each from 29 states and the District of Columbia (Figure 1). About one-third (3338/10,129, 32.95%) of participants resided in an NHBS city, and about the same proportion (3680/10,129, 36.33%) lived in an urban county. Overall, 6.08% (616/10,129) of participants were living with HIV, 66.39% (6725/10,129) were HIV negative, and 27.52% (2788/10,129) had an unknown HIV status. All participant characteristics differed significantly based on the recruitment source, except NHBS city resident (Table 2).

Approximately two-thirds (6926/10,129, 68.37%) of participants reported having anal sex without a condom with another male in the past 12 months, and about one-fifth (2390/10,129, 23.59%) of participants reported doing so with a partner of a discordant or an unknown HIV status (Table 3). Compared with HIV-negative or unknown status participants, those who were living with HIV were significantly more likely to report anal intercourse without a condom (aOR 2.02, 95% CI 1.63-2.50), including with male partners who were of a discordant or an unknown status (aOR 3.90, 95% CI 3.27-4.66). Stratified by the serostatus group, anal intercourse without a condom differed significantly for only HIV-negative or unknown status participants by race or ethnicity, age group, and recruitment website. Anal intercourse without a condom with partners of a discordant or an unknown HIV status differed significantly by race or ethnicity, residence in an NHBS city, and recruitment type for HIV-negative or unknown status participants only.

In total, 31.93% (3235/10,129) of participants reported using marijuana, 2.31% (234/10,129) reported using methamphetamines, and 20.43% (2069/10,129) reported using other illicit substances in the past 12 months (Table 4). Compared with participants with HIV negative or unknown status, HIV-positive participants were significantly more likely to report the use of marijuana (aOR 1.39, 95% CI 1.15-1.68), methamphetamines (aOR 3.42, 95% CI 2.41-4.87), and other illicit substances (aOR 1.90, 95% CI 1.56-2.32) in the past 12 months. Among HIV-positive participants, the use of marijuana varied significantly by age, and the use of other illicit substances varied significantly by race or ethnicity. In addition, the use of marijuana, methamphetamines, and other illicit substances differed significantly by age and race or ethnicity among HIV-negative or unknown status participants. In this group, the use of marijuana and other illicit substances differed significantly by residence in an NHBS city, and the use of marijuana differed significantly by the recruitment website.

HIV testing behaviors were examined among participants who were not HIV positive (Table 5). Most participants (6836/9513, 71.85%) were previously tested for HIV infection, and 52.51% (4995/9513) of the participants were tested in the past 12 months. HIV testing behavior, both ever tested and tested in the past 12 months, differed significantly by age, residence in an NHBS city, and type of recruitment website.

In total, 42.59% (4314/10,129) of participants reported sexually transmitted infection (STI) testing in the past 12 months, and 10.08% (1022/10,129) of participants reported a diagnosis of STI in the past 12 months. Compared with HIV-negative or unknown status participants, HIV-positive participants were significantly more likely to report STI testing (aOR 3.50, 95% CI 2.89-4.24) and STI diagnosis (aOR 2.61, 95% CI 2.10-3.25) in the past 12 months (Table 6). The most common STI diagnosis among HIV-positive participants was syphilis (78/616, 12.7%), followed by gonorrhea (64/616, 10.4%) and chlamydia (62/616, 10.1%). Gonorrhea was the most common STI diagnosis among HIV-negative or unknown status participants (542/9513, 5.69%), followed by chlamydia (520/9513, 5.47%) and syphilis (282/9513, 2.96%). STI testing and diagnosed with any STI significantly differed by age, residence in an NHBS city, and recruitment website among HIV-negative or unknown status participants. Among HIV-positive participants, STI testing only significantly differed by residence in an NHBS city.