Table 1. Characteristics of the included studies.

Author, year (name of the study)	Population, geographic location, age in years	Type of study	Participants enrolled, follow-up	Safer sex counseling	Education / income	Alcohol and recreational drug consumption	Risk behaviour	STI at BL
Double-blind, placebo-controlled RCTs; Participants not aware of group allocation
Grant et al. 2010 [23]; Solomon et al. 2014 [43]; Marcus et al. 2014 [42] (iPrEX)	MSM and transgender women at high risk for acquisition of HIV infection; Lima and Iquitos, Peru: 1400 (56.0%); Rio de Janeiro and Sao Paulo, Brazil: 370 (14.8%); Guayaquil, Ecuador: 300 (12.0%); San Francisco and Boston, USA: 227 (9.1%); Chiang Mai, Thailand: 114 (4.6%); Cape Town, South Africa: 88 (3.5%); mean age: 27.5 (verum), 26.8 (placebo); range: 18–67	Parallel-group RCT (daily TDF + FTC vs. placebo)	2499 randomized; 3324 person-years; duration of observation: median, 1.2 years	Risk-reduction counseling, free condoms, STI screening and treatment	- less than secondary: 523/2499; - secondary: 883/2499; - post-secondary: 1064/2499	No. of alcoholic drinks (on days when subject drank): - 0: 390/2499; - 1–4: 693/2499; - 5+: 1353/2499	No. of partners (past 12w): mean 18±43; unprotected receptive anal intercourse (past 12w): 1485/2499; unprotected anal intercourse (past 6m): 2001/2499; trans-actional sex (past 6m): 1027	- serum HSV-2: 888/2484 (35.75%); - urine leukocyte esterase positive: 45/2499 (1.80%); - current Hep B infection: 13/2499 (0.52%); - syphilis: 333/2499 (13.33%)
Hosek et al. 2013 [24] (PrEPare)	Young (18-22y) MSM with at least one episode of unprotected anal intercourse within the last 12 months; Chicago, USA; mean age: 19.97 +/- 1.3	partly double-blind parallel-group RCT (daily TDF + FTC vs. placebo vs. no pill)	68 pts. were enrolled, 58 randomized (study enrolment was discontinued after discussion of the iPrEx study results)	Many Men, Many Voices (3MV) prevention intervention: risk-reduction counseling, free condoms, STI screening and treatment	High school diploma 18/58 (31.03%); some college: 30/58 (51.72%); unemployed 32/58 (55.17%); received some form of public assistance in their lifetime: 78%	n.r.	Unprotected anal intercourse (past 30 days): 24/58 (41.38%); transactional sex: 10/58 (17.24%)	syphilis: 5/58 (8.6%); chlamydia: 2/58 (3.4%); genital herpes: 1/58 (1.7%); molluscum contagiosum 1/58 (1.7%)
Molina et al. 2015 [26] (IPERGAY)	MSM and transgender women with history of unprotected anal sex with at least two partners during the past 6 months; Paris, Lyon, Nice, Tourcoing and Nantes, France: 357 (89.2%); Montreal, Canada: 43 (10.8%); median age: 35 (IQR 29–43) in verum and 34 (29–42) in placebo group	double-blind parallel-group RCT (on-demand TDF + FTC vs. placebo)	414 pts. randomized, 400 followed; 431.3 person-years of follow-up; median follow-up of 9.3 months	Risk-reduction counselling (according to the RESPECT risk-reduction model), free condoms and gel, STI screening and treatment	Postsecondary education: 287/400	>5 Alcoholic drinks per day in past month: 91/400; Use of recreational drugs: 177/400	median number of partners in past 2 m: 8; Median no. of episodes of sexual intercourse in past 4w: 10	Any STI: 111/400 (27.8%)
Double-blind, active-controlled RCT; Participants not aware of group allocation
Gulick et al. 2017 [44]	MSM or transgender women who had anal intercourse without a condom in the previous 90 days; Baltimore, Boston, Cleveland, Chapel Hill, Los Angeles, Newark, New York, Philadelphia, Pittsburg, San Francisco, Seattle, San Juan (Puerto Rico) and Washington DC, USA; median age 30, range 18–70	double-blind RCT (daily maraviroc vs. daily maraviroc + FTC vs. daily maraviroc + TDF vs. daily TDF + FTC)	406 pts. randomized, 343 (84%) completed	risk-reduction counseling, condom distribution, and HIV testing	less than high school: 3%; high or trade school: 17%; some college: 36%; finished college: 31%; advanced degree: 13% full-time employment: 52%; part-time: 23%; unemployed: 25%	n.r.	n.r.	31 (8%) had an STI; chlamydia in 15 (4%); gonorrhea in 5 (1%); and syphilis in 14 (3%)
Open-label, placebo-controlled RCT; Participants aware of group allocation, for calculation of STI incidence only data from PrEP group used
McCormack et al. 2016 [25] (PROUD)	MSM who had anal intercourse without a condom in the previous 90 days; Birmingham, Brighton, London, Manchester, Sheffield, and York, UK; median age 35 (IQR 29–43)	open-label RCT (daily TDF + FTC vs. deferred PrEP)	523 contributed to HIV incidence analysis (both study groups); 465 person-years of follow-up; 243 person-years of follow-up in the immediate group	Risk reduction interventions were offered according to routine practice at the clinic	327/540 (61%) university graduates	231/525 (44%): one or more drugs associated with sexual disinhibition (γ-hydroxybuty-rate, 4-methylmeth-cathinone, or methamphetamine) (past 90 days)	21% of participants allocated to immediate PrEP reported receptive anal sex with ten or more partners without a condom at one year	331/517 (64%) STI (previous 12m); 172/517 (33%) rectal gonorrhoea or chlamydia (previous 12m); 184/510 (36%): at least one course of PEP (previous 12m)
Cohort studies of PrEP users
Bristow et al. 2018 [45] (abstract only)	MSM and transgender women at risk for HIV; South California (four urban medical centers), USA	cohort study	394 participants; 238 PY of follow-up (for Chlamydia of the throat) to 485.1 PY (for urethral gonorrhea)	n.r.	n.r.	n.r.	n.r.	n.r.
Cotte et al. 2018 [46]	HIV- and HCV-negative MSM enrolled in a PrEP program; France; median age 37 years (IQR 30–45)	cohort study	930 HIV-negative MSM were enrolled for PrEP; follow-up was available for 916 of these, accounting for 972 PY of follow-up	n.r.	n.r.	n.r.	n.r.	17 participants HCV infected at BL; prevalence 1.8%; 14 cured, 3 active HCV infection
Golub et al. 2016 [47] (SPARK) (abstract only)	MSM and transgender women at risk for HIV acquisition; New York, USA	cohort study (RCT on behavioral interventions to increase adherence to PrEP)	280 began PrEP; 179.5 person-years of follow-up	not reported (data were derived from an RCT on behavioral interventions; assignment to groups not reported in the present conference abstract)	n.r.	n.r.	n.r.	any STI: 31/280 (11.1%) rectal STI: 25/280 (8.9%) urethral STI: 5/280 (1.8%) syphilis: 3/280 (1.1%)
Grant et al. 2014 [31] (iPrEX_OLE)	MSM and transgender women at high risk for acquisition of HIV infection (from various PrEP trials); Lima and Iquitos, Peru: 562 (45.9%); Chicago, San Francisco, Boston, and Atlanta, USA: 224 (18.3%); Rio de Janeiro and Sao Paulo, Brazil: 192 (15.7%); Guayaquil, Ecuador: 153 (12.5%); Chiang Mai, Thailand: 54 (4.4%); Cape Town, South Africa: 40 (3.3%); no data on mean / median age; 59% of pts were 25–39 years old	cohort study (open-label extension of previous PrEP RCTs, offering all pts. daily TDF + FTC)	1603 pts. were enrolled, among these 1128 started PreP at enrolment, 378 never started PreP and 97 started PreP after enrolment	Counselling targeted PrEP-adherence and -reporting; this involved counselling for sexual health	Less than secondary: 327/1590; Secondary: 547/1590; Post-secondary: 716 /1590	Alcohol use: <Once a month: 144/1603; 1–4 drinks on days when drinking: 508/1603; ≥5 drinks on days when drinking: 324/1603 Methamphetamine use: 31/1593 Cocaine use: 133/1539	519/1603 reported condomless receptive anal intercourse	Syphilis rapid plasma reagin positive: 253/1603; Herpes simplex virus-2: 791/1603; Gonorrhoea: 31/1587
Grinsztejn et al. 2018 [32] (PrEP Brasil)	MSM and transgender women who reported one or more sexual risk criteria in the previous 12 months (eg, condomless anal sex with two or more partners, two or more episodes of anal sex with an HIV-infected partner, or history of STI diagnosis); Rio de Janeiro and Sao Pauo, Brazil no data on mean age; 47.6% aged between 25 and 34 years	cohort study PrEP (TDF + FTC)	450 participants were enrolled, 375 were retained at 48 weeks	Brief risk reduction counselling and a short adherence support session	Length of schooling, years <12: 115/450 (25.6%); >/ = 12: 335/450 (74.4%)	Binge drinking: 241/375 (64.3%); Stimulant use: 77/375 (20.5%)	≥2 condomless anal sex partners in previous 12 months: 294/365 (80.5%); Anal sex with HIV-infected partners: 223/450 (49.6%); STI in the previous 12 months: 207/450 (46%)	Rectal chlamydia: 36/450 (8%); rectal gonorrhea: 22/450 (5%)
Hoornenborg et al. 2018 [48,49] (abstracts only) (AmPrEP)	MSM and transgender persons who have sex with men, who were at least 18 years old and had one or more risk factors for HIV infection in the past 6 months; Amsterdam, Netherlands	cohort study (daily or event-driven PrEP with TDF + FTC)	376 participants were included in the analysis; for these participants median follow-up was 1.76py	n.r.	n.r.	n.r.	n.r.	n.r.
Hosek et al. 2017 [34]	Young (18–22 years) MSM who reported HIV transmission risk behavior (eg, condomless anal intercourse, multiple sexual partners, or recent STI) in the last six months; Baltimore, Boston, Chicago, Denver, Detroit, Houston, Los Angeles, Memphis, Miami, New Orleans, Philadelphia, and Tampa, USA mean age 20.2 (SD 1.3)	cohort study (daily TDF + FTC)	200 pts. were enrolled, and 58 prematurely discontinued; overall study retention was 71%, including premature discontinuations and those who were lost to follow-up.	Prevention services at each visit included risk reduction counseling, condoms, and an Integrated Next Step Counseling session.	completed some college: 45.5%; currently unempoyed: 30.1%	n.r.	Average sex partners in previous month: 5; Condomless sex previous month: 80.8%; Condomless receptive anal intercourse with last partner: 58.0%; Any positive STI test: 22%; Ever exchanged sex for money: 28.6%	22% of pts. were diagnosed with an STI
Hosek et al. 2017 [33] (PrEPare)	Young (15–17 years) MSM who reported condomless anal intercourse with a partner of unknown or positive HIV serostatus, anal intercourse with at least three male partners, exchange sex, or sexually transmitted infection in the last six months; Boston, Chicago, Denver, Los Angeles, New Orleans, and Philadelphia, USA; mean age 16.5 (SD 0.73)	cohort study (daily TDF + FTC)	78 pts. were enrolled, 72 (92%) began daily oral PrEP and 46 (64%) of these completed 48 weeks of follow-up	Evidence-based personalized cognitive counselling intervention to reduce sexual risk and comprehensive HIV prevention package (including HIV testing, sexual health and adherence promotion using Integrated Next Step Counselling, free condoms, and safety assessments)	Currently attending school: 56/78 (72%); Eighth grade or less: 3/78 (4%); More than eighth grade but high school not completed: 58/78 (74%); GED: 3/78 (4%); High school diploma: 11/78 (14%); Some college: 1/78 (1%)	Alcohol consumption in the past month every week or more: 9/78 (12%); Got drunk in the past month once or more: 33/78 (67%); Smoked marijuana in the past month once or more: 47/78 (63%)	Have been paid for sex (lifetime): 13/78 (17%); unprotected receptive anal sex: 24 (60%); median number of male partners with sexual contacts: 1 (IQR: 1–2)	19 prevalent STIs were diagnosed in 14/78 pts (18%); rectal gonorrhea: 5/78 (6.4%); rectal chlamydia: 8/78 (10.3%); urethral chlamydia 4/78 (5.1%); syphilis 2/78 (2.6%)
Lal et al. 2017 [27] (VicPrEP)	MSM at risk of HIV infection (condomless receptive or insertive intercourse with an HIV seropositive person, receptive condomless anal intercourse with casual partners of unknown HIV status, or uncircumcised, condomless insertive anal intercourse with casual partners of unknown HIV status); Melbourne, Australia; median age 34.0 (IQR 30.8–45.0)	cohort study (combined daily TDF + FTC)	114 pts. were enrolled; STI data from 105 pts. were available at month 12; 107.2 person-years of follow-up	Safer sex practices, including condom use, were recommended at each study visit	64.1% had completed an undergraduate or higher degree	n.r.	97/114 had casual partners, with a mean of 19.2 anal sex acts in the past 3 months	12.3% had a new STI diagnosis at baseline
Lalley-Chareczko et al. 2018 [50]	Young (18–30 years) MSM and transgender women of colour; Philadelphia, USA; mean age 22.1 (range 18–29 years; SD 2.97)	cohort study	50 participants enrolled; 90% retention at 12 weeks, 74% retention at 24 weeks, 70% retention at 36 and 48 weeks	Standard HIV prevention services including condom provision, risk reduction counseling, HIV testing, and STI screening and treatment	n.r.	Drug/alcohol use: 37/50 (74%)	HIV-positive partner: 4 (8%); Partner(s) of unknown HIV status: 27 (54%); Inconsistent condom use: 40 (80%); History of STI: 29 (58%); Exchange of sex for commodities: 9 (18%); 4 or more partners in last 6 months: 15 (30%)	6 / 50 (12%) tested positive for rectal chlamydia and/or gonorrhea
Liu et al. 2016 [28] (US PrEP Demonstration Project)	MSM and transgender women who reported any of the following in the last 12 months: condomless anal sex with ≥2 male or transgender female partners; ≥2 episodes of anal sex with ≥1 HIV-infected partner; or sex with a male/transgender female partner and having a diagnosis of syphilis or rectal gonorrhea or chlamydia; San Francisco / Miami / Washington, USA; no data on mean / median age; 63% of pts were 26–45 years old	cohort study (daily TDF + FTC)	557 pts. enrolled, 437 pts. were retained in the study; 481 person-years of follow-up	client-centered risk-reduction counseling, free condoms and lubricants, linkages to appropriate community services	High school or less: 55/437; Some college: 119/437; College graduate: 156/437; Any postgraduate: 107/437; <20,000$: 128/437; 20,000–59 999$: 158/437; ≥60,000: 139/437	recreational drug use: 326/437; polysubstance use: 94/437; amphetamine use: 71/437; injected drug use: 7/437; alcohol (≥5 drinks per session, past 3m): 47/437	mean number of anal sex partners (past 3 months): 10.9; condomless receptive anal intercourse: 365/557 (65.5%)	147/557 (26.4%) had early syphilis, N. gonorrhoeae, or C. trachomatis at baseline
Marcus et al. 2016 [29] (‘Kaiser Cohort Northern California’) Comment below	PrEP users (Kaiser Permanente NC members); Northern California, USA; mean age 37.5 years (SD 10.1, range 18–68)	cohort study (daily TDF + FTC)	972 PrEP initiators; 850 person-years of PrEP use; mean duration during study period was 0.9 years per person	adherence support	% without high school diploma in census block, mean (SD) 11.5 (11.1); median household income in census block, USD (IQR) 74,094 (52,273–99,231)	history of alcohol/drug abuse: 6.3%	n.s.	STI at baseline: 15.9%
Molina et al. 2017 [30] (IPERGAY open-label extension)	MSM and transgender women with history of unprotected anal sex with at least two partners during the past 6 months; Paris, Lyon, Nice, Tourcoing, and Nantes France: 320 (89%); Montreal, Canada: 41 (11%); median age 37 years (IQR 30–44)	cohort study (on-demand TDF + FTC)	361 were enrolled; 63 (17%) prematurely discontinued; median follow-up time was 18.4 months (IQR 17.7–19.1); 518 person-years of follow-up for the assessment of HIV incidence	Comprehensive package of prevention services, including face-to-face risk-reduction counselling done by a peer community member, and free condoms and gel.	Postsecondary school: 324/355 (91%); Other: 31/355 (9%)	Use of recreational drugs for sex: 157/356 (44%)	No. of partners in past 2 months: median 7 (IQR 3–15); No of sexual acts in past 4 weeks: median 9.5 (IQR 5–15); Condomless receptive anal sex in most recent sex act: 136/176 (77%)	n.r.
Nguyen et al. 2018 [51]	PrEP users, considered at high risk based on reporting at least one seropositive sexual partner with a detectable viral load, or engaging in condomless anal sex with multiple partners whose HIV status was unknown. Montreal, Canada; median age 36 years (IQR 31–44)	Retrospective cohort study (PrEP, offered as a once-daily or intermittent regimen; evaluation of STI incidence for participants for whom a 12 months follow-up was available)	109 participants; 109 PY of follow-up	n.r.	Education: - Primary 1 (1.4%) - Secondary 9 (12.5%) - College 11 (15.3%) - University 51 (70.8%) Income: - <$10 000 3 (3.4%) - $10 001–20 000 12 (13.6%) - $20 001–35 000 7 (8.0%) - $35 001–55 000 17 (19.3%) - $55 001–75 000 21 (23.9%) - >$75 000 28 (31.8%)	n.r.	Number of sexual partners within 12 months prior to PrEP: - Stable, median (IQR) 1 (1–2) - Casual, median (IQR) 20 (10–40)	n.r.
Noret et al. 2018 [52]	MSM or transgender persons who reported having had condomless anal sex with at least 2 different partners over the last 6 months, and/or an STI over the last 12 months, and/or multiple courses of PEP within the prior 12 months, and/or use of chemsex. Paris, France; median age 36 years (IQR 26–42)	cohort study (on demand or daily TDF + FTC)	1049 participants were enrolled; 887 (84.5%) were still under follow-up at the end of study; 486 person-years of follow-up	Comprehensive package of prevention services including free condoms and gel and patient-centered counseling for risk reduction performed by a peer community member, to discuss the risks of HIV and other STIs.	Post-secondary education: 880 / 1043 (84.4%)	Use of chemsex in the last 4 weeks: 437 / 1027 (42.6%); Use of chemsex at last sexual intercourse: 279 / 1016 (27.5%)	Number of partners in past 3 month: median: 10 (IQR: 5–10); Number of condomless sexual intercourses acts (prior 4 weeks): median: 4 (IQR: 1–10); Participants reporting condomless sex at last intercourse: 557 / 1045 (53.3%); Participants reporting condomless receptive anal sex at last intercourse: 315 / 1031 (30.6%)	at least one bacterial STI at BL: 146 / 998 (14.6%); Chronic Hep C: 9 / 998 (0.9%); Chronic Hep B: 5 / 998 (0.5%)
Volk et al. 2015 [53] ('Kaiser Cohort San Francisco')	PrEP users (Kaiser Permanente SF members); San Francisco, USA	cohort study (daily TDF + FTC)	485 PrEP users; 304 person-years of PrEP use	n.r.	n.r.	n.r.	n.r.	n.r.

BL, baseline; FTC, emtricitabine; m, months; n.r., not reported / not assessed; No., number; PrEP, pre-exposure prophylaxis; PY, person-years; STI, sexually transmitted infection; TDF, tenofovir disoproxil fumarate; w, weeks; y, years; Comment: Data on incidence rates of STI in the study by Dr. J. Marcus were derived from data supplied in personal communication.