The successful demonstration of PrEP efficacy 
may offer a new way to curtail the increasing number of new HIV infections among MSM in the U.S. 
and around the world 
. Increasingly, MSM are meeting partners and obtaining health information through the internet 
. The current study of MSM engaged in online social networking showed that there was an increase in PrEP awareness among a sample interviewed after the publication of the iPrEx results compared with a sample interviewed before iPrEx. Although the current study demonstrated that knowledge of PrEP immediately after iPrEx was limited overall (19%), this is not surprising as the diffusion of new knowledge clearly takes time. However, once chemoprophylaxis was described to the men, interest in PrEP use was high.
The majority of the men sampled on this online sexual network were highly educated and affluent; these demographic characteristics are consistent with those that have been previously associated with increased PrEP awareness 
. These men are likely to represent a relatively knowledgeable subset of U.S. MSM regarding new prevention findings, so studies to assess PrEP awareness among representative samples of MSM are still needed. In this study, men who were not familiar with PEP and those who only had male partners were less likely to know about PrEP, so strategies to increase PrEP uptake for this population of MSM will need to be focused on providing information and education. MSM who were older, who reported recent UAI with a man and/or perceived themselves to be at increased risk of HIV acquisition more often indicated interest in using PrEP. This suggests that some MSM who may benefit from PrEP might be open to using it as a protective intervention. In this group, efforts should be focused on facilitating access to healthcare providers who can help individuals make informed decisions regarding PrEP use. For MSM who are younger, as well as those who may misperceive or deny their risks, education regarding risk assessment should be stressed as this will not only increase identification of those MSM who may benefit from PrEP, but could also increase utilization of HIV and STI testing.
MSM who reported prior knowledge of PEP were at 30-fold greater odds of having heard about PrEP but at nearly half the odds of expressing interest in using it, yet MSM who had used PEP were more likely to report PrEP use. A possible explanation for this paradox is that MSM who had heard about PEP, but had not used it, may have concerns about chemoprophylaxis in general, whereas those who had actually used PEP were more willing to try a similar intervention. Further studies to understand how perceptions and experiences with PEP affect attitudes and decisions regarding PrEP are needed.
The current study found minimal evidence of immediate uptake of PrEP in this community despite the fact that a majority of MSM were interested in using PrEP. It is understandable that there was limited PrEP use given the fact that the iPrEx results were released only a month prior to the second survey and implementation of medical innovations do not occur in that time frame. However, this study suggests that additional impediments to PrEP uptake may exist, as nearly 1 in 5 MSM surveyed in this study had heard of PrEP, but less than 1 in 100 had taken it. Unclear payment mechanisms could be among these barriers given estimated costs of PrEP use of $10 000 per person annually 
. Issues related to patient-provider communication could also limit PrEP provision, as a substantial proportion of at-risk MSM in this study had not discussed risky sexual behaviors or ways to protect against HIV acquisition with a primary care provider. Therefore, it is important to improve training of providers so they become comfortable discussing MSM sexuality in an effort to identify MSM who would be most likely to benefit from PrEP. Clinicians may also be cautious about prescribing PrEP due to concerns regarding potential unintended consequences of PrEP use 
, such as toxicities, risk compensation 
, or development of drug resistance 
. A cross-sectional survey of generalist physicians and HIV specialists in Massachusetts showed that after iPrEx, nearly all providers (92%) were aware of oral PrEP and most (76%) would be willing to prescribe it to high-risk MSM based on the results of the iPrEx study, though data to suggest the aforementioned consequences could dissuade them [Mayer et al., unpublished data]. It will be important to provide physicians with accurate data on the risks and benefits of PrEP and tools to help them communicate this information to MSM so they can share in evidence-based decision making regarding PrEP prescribing. Further studies are needed to understand facilitators and barriers to implementing this new intervention.
This study has several limitations. The most notable is that data was drawn from two different samples, using two different recruitment methods (i.e., inviting the most active users pre-iPrEx versus all members of this network post-iPrEx), resulting in different sample sizes. As such, the observed increase in PrEP awareness could potentially reflect sampling differences and not a true increase in knowledge. However, the study samples were similar with respect to variables that have previously been associated with greater PrEP awareness, such as level of PEP knowledge, education and income 
, so a bias towards increased awareness post-iPrEx is unlikely. Additional limitations suggest that participants are not representative of at-risk MSM in general. First, while the number of participants in this study was high, there was a low response rate overall (22.2% pre-iPrEx and 27.3% post-iPrEx). Other studies utilizing internet recruitment of MSM have reported rates of participation ranging from 5%–61% 
. Reassuringly, participant demographics in this study sample were comparable to those found in other recent studies involving members of the same online network 
, making it more likely that the study sample accurately represents the network's demographics. Second, study completion rates were modest with only two-thirds of participants responding to all survey questions. However, the pattern of missing data was most consistent with non-completion of surveys because of fatigue 
, and would therefore be unlikely to bias the results of the PrEP-related outcomes asked early in the survey. Third, participants were recruited online. Yet this limitation also provides a strength in that previous studies have demonstrated that online data collection has the potential to limit social desirability bias and result in more honest and accurate responses 
. Finally, the mean age of participants was 40 years and >80% were white, so they are not representative of some of the highest risk groups, such as young black and Latino/Hispanic MSM 
. However, nearly 40% of new infections among U.S. MSM occur in whites 
, so the study findings are likely to be relevant for a substantial population of at-risk MSM.
The findings of modest awareness, substantial interest, and minimal use of PrEP among MSM using a popular social networking website immediately after publication of iPrEx results suggests that informational campaigns are needed to raise awareness of PrEP and facilitate dialogues among at-risk MSM and their providers. As the internet may provide an effective means for disseminating risk reduction campaigns among at-risk MSM 
, web-based informational programs about PrEP that are targeted to this population are warranted. In addition, prospective studies are needed to understand MSM- and provider-related barriers to discussing HIV risk behaviors and initiating PrEP in the clinical setting. As efforts continue to focus on the use of biomedical interventions for HIV prevention, translation of PrEP interest into effective use of chemoprophylaxis remains a priority among strategies to decrease the rate of new HIV infections among high-risk populations.