“The study findings highlight the importance of conducting drug resistance testing at the time of HIV diagnosis in order to guide treatment decisions,” said Dr. Hong-Ha Truong, Assistant Professor of Medicine at the University of California, San Francisco and lead author of the study.

The study authors noted that the high proportion of non-nucleoside reverse transcriptase inhibitor (NNRTI) resistant cases was worrisome, since the NNRTI Sustiva (efavirenz) is a component of Atripla (efavirenz/emtricitabine/tenofovir), the most commonly prescribed regimen for patients beginning antiretroviral therapy.

“NNRTIs should be avoided if mutations conferring resistance to this drug class are detected,” said Dr. Truong.

However, the authors also noted that the results from this study may not necessarily hold true for populations at other sites in the nation, because a large proportion of participants in the study were men who have sex with men.

In HIV-positive people taking antiretroviral drugs, mutations in the HIV virus may lead to the development of drug-resistant variants of the virus. These resistant forms of HIV can be passed on from one person to another, rendering the newly infected person unresponsive to certain antiretroviral drugs. Drug resistance in people newly diagnosed with HIV is called transmitted drug resistance.

Previous research has shown that even low levels of drug-resistant HIV can increase the risk of treatment failure by two to three fold (see related AIDS Beacon news).

In this study, researchers at the University of California, San Francisco aimed to identify the infection stage (acute, recent, or long-term) of persons newly diagnosed with HIV and to describe the rate of transmitted drug resistance. The researchers also looked for genetic and lifestyle factors that were associated with infection stage and transmitted drug resistance.

The study authors analyzed data collected from 9,868 individuals who used the voluntary HIV counseling and treatment program at San Francisco’s municipal Sexually Transmitted Infection Clinic. Almost 85 percent of participants were men, 69 percent were between 25 and 44 years of age, and 54 percent were Caucasian. Most individuals included in the analysis (73 percent) were men who have sex with men.

Among individuals who tested positive for HIV, those who still had low anti-HIV antibody levels in their blood were classified as recently infected; the rest were designated as long-term infected. Individuals who tested negative for HIV underwent more sensitive testing that looks for the presence of viral genetic material in the blood. This helped identify individuals who had been infected so recently with HIV that their immune system had not yet made antibodies against it (acute infection).

“Acute infection testing is important because it identifies persons with HIV during a highly infectious period,” said Dr. Truong.

Viruses from newly diagnosed individuals were then screened for mutations that rendered them resistant to different classes of antiretroviral drugs.

Results showed that the occurrence of new HIV diagnoses, acute infections, recent infections, and transmitted drug resistance remained stable from 2004 to 2006. However, a separate analysis of men who have sex with men revealed an increasing number of HIV cases in this group.

About 4 percent of individuals tested were HIV positive. Of these, 59 percent were long-term infected, 34 percent were recently infected, and 8 percent were acutely infected.

Male gender, amphetamine use, sex with a known HIV-positive partner, African-American ethnicity, and a history of gonorrhea were associated with an increased risk of recent infection.

Results from the study also indicated the presence of transmitted drug resistance in 13 percent of newly diagnosed individuals. Among individuals with transmitted drug resistance, 77 percent were men who have sex with men.

Nearly 60 percent of the mutations observed conferred resistance to NNRTIs. About 30 percent of mutations provided resistance to nucleoside reverse transcriptase inhibitors and another 30 percent to protease inhibitors. The proportion of cases with resistance to protease inhibitors increased over time.

For further information, please see related article in PLoS One.

Based on their results, the authors emphasized the need to counsel women about the possible increase in HIV risk with hormonal contraceptive use, especially the shot Depo-Provera, and the importance of condom use to decrease risk of HIV.

“Women should be counseled about potentially increased risk of HIV acquisition and transmission with hormonal contraception, particularly injectable methods, and about the importance of dual protection with condoms to decrease HIV risk,” said Renee Heffron, a researcher at the International Clinical Research Center at the University of Washington and lead author of the study, in a press release.

The researchers advocated further studies of other hormonal contraceptives, such as implants or patches, to determine whether they also affect HIV acquisition and transmission risk. They also argued that contraceptive counseling should be combined with HIV counseling and testing.

The results were first presented in July at the 6th International AIDS Society Conference on HIV Pathogenesis, Treatment, and Prevention in Rome.

According to the study authors, the prevention of unintended pregnancy in women with or at risk for HIV has benefits that include reduced mother-to-child transmission of HIV and improved health of children through spacing of pregnancies.

Many women throughout the world use hormonal birth control, which includes birth control pills and injected contraceptives such as Depo-Provera (depot medroxyprogesterone acetate). However, the effects of hormonal contraception on HIV risk are unclear; according to the authors, some studies have investigated the association between hormonal birth control and the risk of HIV acquisition and transmission but results have been conflicting.

In this study, researchers followed nearly 3,800 serodiscordant couples in seven African countries from 2004 to 2010. Serodiscordant couples are couples in which one partner is HIV-positive and the other partner is HIV-negative.  In most of the couples in this study, the partner infected with HIV was female.

All participants were aged 18 years or older, were sexually active, and were not using antiretroviral therapy. Additionally, all HIV-positive partners in the trial had herpes simplex virus type 2.

The researchers monitored rates of HIV-acquisition by HIV-negative women taking oral hormonal contraceptives or who received Depo-Provera shots. They also monitored rates of HIV-transmission from HIV-positive women taking hormonal contraceptives to their HIV-negative male partners.

All participants received HIV-prevention services, including counseling, free condoms, and treatment for sexually transmitted infections.

Results showed that HIV-negative women who used hormonal contraception, either in pill form or injected, were twice as likely to contract HIV from their HIV-positive male partners as women who reported using other forms of birth control or no birth control.

In addition, HIV-positive women who used hormonal contraception were twice as likely to transmit the virus to their uninfected partners as women who did not.

However, the study authors noted that not enough women in the study used birth control pills (rather than Depo-Provera) to draw definitive conclusions about the pill form of contraceptives.

The study authors also found that women using Depo-Provera had higher levels of HIV in the genital tract, even though the levels of HIV in their blood were the same. The researchers suggested that the higher level of HIV in the female genital tract might be a mechanism for increased risk of HIV transmission.

The researchers stated that a randomized trial is needed to definitively establish the risk of HIV associated with the contraceptives since the current study did not take into account factors such as contraception adherence and brand of contraception used.

For more information, please see the article in The Lancet Infectious Diseases (abstract) or the press release from the University of Washington.

The authors of the study recommended that further studies be conducted to assess the influence of socioeconomic and other factors on HIV transmission. They also suggested that more effort is put into the development of more effective HIV prevention and intervention strategies.

According to the study authors, previous studies have suggested that there has been an increase in sexual transmission of HIV from HIV-positive individuals who know they are infected but still engage in unprotected sex. Unprotected sex also puts people with HIV at risk of contracting other sexually transmitted infections such as gonorrhea and chlamydia.

Research has also shown that misunderstandings about HIV, lack of knowledge about HIV transmission and protective sexual behaviors, and factors such as depression and anxiety are associated with risky sexual practices in people with HIV.

In this study, researchers investigated if depression and anxiety as well as knowledge of HIV and other factors contributed to the likelihood of men with HIV having unprotected sex.

The authors reviewed 17 published studies that examined psychological and social factors that influence risky sexual behavior in people with HIV. They then performed a statistical analysis on the results from these studies to determine which factors had the greatest influence on unsafe sex practices.

Results showed that knowing less about HIV, believing that safe sex decreases sexual pleasure, and having less intention of engaging in condom use and safe sex practices were associated with an increased likelihood of unprotected sex.

In addition, men who were less committed to practicing safe sex, either for their own benefit or someone else’s, were more likely to have unprotected sex.

Depression, anxiety, and emotional distress were also associated with an increased risk of having unprotected sex, as were less satisfaction with life and a greater number of sexual partners.

For more information, please see the study in AIDS Care (abstract).

“Based on the results, we are now offering [antiretroviral therapy to] all HIV-infected participants in the delayed arm, regardless of CD4 count,” said Dr. Myron Cohen, who presented the results today at the 6th International AIDS Society Conference on HIV Pathogenesis, Treatment, and Prevention (IAS 2011). The results were also released today in the New England Journal of Medicine.

The study authors recommended that antiretroviral therapy be further considered as a treatment strategy for preventing HIV transmission. They also stated that a longer follow-up period is necessary before they can give a recommendation on whether earlier antiretroviral treatment is beneficial to people with HIV for health reasons.

The Phase 3 clinical trial, which included participants in Boston as well as in international locations such as India and Africa, was designed to test whether people with HIV who start treatment earlier are less likely to transmit the virus to their partners. This strategy is known as “treatment as prevention” and rests on the idea that people taking antiretrovirals will have lower levels of HIV in their blood, semen, and vaginal fluids, reducing the risk of transmission.

This is in contrast to pre-exposure prophylaxis, a different strategy in which uninfected men and women take antiretrovirals to prevent infection from their HIV-positive partners. Results from two large studies that were released last week showed that pre-exposure prophylaxis is also effective at reducing transmission (see related AIDS Beacon news).

The new study included 1,763 serodiscordant couples in which one partner was HIV positive and the other HIV negative. In half of the couples, the HIV-positive partner was assigned to start treatment immediately upon enrolling in the study at CD4 (white blood cell) counts between 350 and 550 cells per microliter. In the other half, the HIV-positive partners started antiretroviral therapy after their CD4 counts dropped to 250 cells per microliter or less or they developed an AIDS-related illness.

Nearly all of the couples (94 percent) were heterosexual, and a majority of participants (61 percent) were between the ages of 26 and 40, with a median age of 32 years. Initial CD4 counts, viral loads (amount of virus in the blood), and reported levels of condom use were similar for couples in the two groups.

All participants received free condoms and guidance on safe sex practices at each study visit. Participants were followed for a median of 1.7 years.

Results showed that starting antiretroviral therapy early reduced the number of illnesses experienced by the HIV-positive partners in the study and significantly reduced transmission of HIV to the HIV-negative partners.

A total of 105 AIDS-related illnesses or deaths occurred during the study, 40 in the early treatment group and 65 in the delayed treatment group, for a total higher risk of 67 percent in the late treatment group. This was primarily due to tuberculosis infections, which occurred in three of the early treatment group participants versus 17 of the late treatment group participants.

Participants in the early treatment group also had higher CD4 counts than the late treatment group a year after starting treatment, with a median of 603 cells per microliter versus 418 cells per microliter, respectively.

In addition, there were a total of 39 HIV transmission events during the study, 28 of which were confirmed to be between partners (rather than from an outside source). One transmission occurred in the early treatment group and 27 in the delayed treatment group, indicating a 96 percent reduction in risk for participants whose HIV-positive partners started treatment early rather than later.

Furthermore, the single confirmed transmission in the early treatment group occurred very soon, within three months, after treatment initiation; all 27 transmissions in the late treatment group occurred before participants started treatment.

The most common side effects in both treatment groups were infections, psychiatric and nervous system problems, metabolic or nutrition problems, and stomach problems; rates of these side effects were similar between the two groups.

However, participants in the early treatment group were more likely to have severe blood-related side effects, such as low white blood cell levels (neutropenia) or abnormal phosphate levels.

For more information, please see the “Treatment is Prevention” conference session, which includes four presentations on the study, at the IAS 2011 website; or the study in the New England Journal of Medicine.

When taken daily, the antiretrovirals reduced transmission risk by 60 percent to 70 percent. Due to the strength of the results one of the two trials was modified to discontinue the placebo group early, with all participants being placed on the drugs for prevention purposes.

“These are exciting results for global HIV prevention. We now have findings from two studies showing that [pre-exposure prophylaxis] can work for heterosexuals, the population hardest hit by HIV worldwide,” said Dr. Kevin Fenton, director of the Centers for Disease Control’s National Center for HIV/AIDS, Viral Hepatitis, Sexually Transmitted Diseases, and Tuberculosis Prevention, in a press release.

The studies are particularly relevant for serodiscordant couples, in which one partner is HIV positive and the other is HIV negative.

Based on the results, the United States Centers for Disease Control and Prevention (CDC) has stated that it will begin working on guidelines for heterosexual men and women in the U.S.

“The next important step is to fully review the data and assess when and how [pre-exposure prophylaxis] should best be used for HIV prevention among heterosexuals,” said Dr. Jonathan Mermin, director of the CDC’s Division of HIV/AIDS Prevention.

Viread And Truvada Decrease HIV Infection Risk

Viread (tenofovir), which is also a component of Truvada (emtricitabine/tenofovir), is an antiretroviral drug marketed by Gilead Sciences. Results from a previous clinical trial showed that a daily dose of Truvada reduced the risk of HIV infection in men who have sex with men by 44 percent (see related AIDS Beacon news).

The purpose of the two new clinical trials was to see if Viread and Truvada are similarly effective in heterosexual serodiscordant couples. The strategy of taking antiretrovirals to prevent HIV infection is known as pre-exposure prophylaxis.

The first trial, conducted by the CDC in Botswana, included 1,219 men and women aged 18 to 39 years. Half the participants received Truvada once daily while the other half took a placebo. All participants were instructed in HIV prevention, including condom use, and tested regularly for HIV.

Preliminary results showed that 9 of 601 participants taking Truvada (1.5 percent) contracted HIV during the study period, compared to 24 of 599 participants taking a placebo (4 percent), for a total reduction in HIV infection risk of 63 percent.

Further analysis showed that participants with steady access to the drugs (excluding those who may not have had access during the entire study period) had an overall risk reduction of 78 percent. The CDC reported no significant safety concerns, with the most common side effects being nausea, vomiting, and dizziness.

The trial is completed but the CDC is still in the process of analyzing the results, including the impact of adherence on the drug’s efficacy.

The second clinical trial, conducted by the University of Washington in Kenya and Uganda, included 4,758 serodiscordant couples. One third of the HIV-negative partners in the study received Viread once daily, one third took Truvada once daily, and the remaining one third received a placebo. As in the CDC trial, all participants were instructed in safe sex practices and tested regularly for HIV.

Results showed a total of 18 new HIV infections among the partners taking Viread, 13 in partners taking Truvada, and 47 among those taking a placebo. The reduction in infection risk was found to be 62 percent for patients taking Viread and 73 percent for patients taking Truvada, although the difference between the drugs was not considered large enough to be statistically significant.

The researchers also found high levels of treatment adherence, with more than 97 percent of assigned doses actually taken. The rates of serious medical problems during the trial were similar for patients receiving the antiretrovirals and those receiving the placebo.

The trial is ongoing but participants receiving the placebo have been switched to taking either Viread or Truvada.

A third clinical trial testing the efficacy of once-daily Truvada in pill form versus as a vaginal gel for pre-exposure prophylaxis is still ongoing.

CDC: Guidelines On Pre-Exposure Prophylaxis For Heterosexual Men And Women Are Coming

As a result of the two successful trials, the CDC plans to release guidelines in the U.S. for use of Viread or Truvada in heterosexual couples. The CDC has recommended that couples wait for the guidelines, which will include topics like how to handle pregnancies, before using the drugs as a preventative measure.

However, for those considering taking Viread or Truvada now, officials at the CDC have issued the following recommendations:

• HIV-negative individuals should confirm, via HIV testing, that they are still HIV negative before starting pre-exposure prophylaxis. They should also continue to be tested regularly for HIV.
• Antiretrovirals taken as a preventative measure should always be combined with other safe sex strategies, such as regular condom use. They are not meant to be a stand-alone barrier to infection.
• The drugs must be taken daily.
• Antiretrovirals should only be used after consulting with a physician and in conjunction with regular monitoring.

The CDC also noted that there is no information yet on whether pre-exposure prophylaxis is effective in injection drug users. There is also insufficient information to provide a recommendation to women who are pregnant, planning to become pregnant, or breastfeeding.

Pre-Exposure Prophylaxis Gains Steam But Is Still Somewhat Controversial

The use of pre-exposure prophylaxis in the U.S. is still somewhat controversial. The AIDS Healthcare Foundation (AHF), a California-based treatment and advocacy group, recently asked the Food and Drug Administration (FDA) not to approve Truvada for pre-exposure prophylaxis, based on the trial results for men who have sex with men (see related AIDS Beacon news).

“The first of our numerous concerns is that the…study results do not pass the threshold for effectiveness. The 44 percent efficacy that was achieved is well below the threshold generally agreed upon as necessary to be considered effective,” wrote AHF.

“The impact of a prophylactic with an efficacy rate of 60 percent would be considered low. It is unclear why the threshold of acceptability has been lowered so significantly in the case of [Truvada].”

The AHF argued that the drug was not effective enough in preventing HIV transmission and could lead to riskier sexual behavior and transmission of drug-resistant HIV. In addition, the AHF pointed to an earlier study showing that Truvada was ineffective at preventing HIV infection in women; it is still unclear why that study was less successful.

However, the new results, which show higher efficacy rates for heterosexual men and women, could increase the probability of Truvada or Viread receiving FDA approval for pre-exposure prophylaxis. Even if not approved, the drugs could still be prescribed “off-label” – for a purpose other than a drug’s approved function – but Gilead would not be able to market the drugs for pre-exposure prophylaxis and insurance companies and government health plans may be less likely to cover it.

For more information, please see the press releases from the CDC and the University of Washington (pdf).

Utah Closes ADAP For New HIV Patients – The Utah Department of Health has closed its AIDS Drugs Assistance Program (ADAP) to new HIV patients. According to the program’s administrator, increasing demand for free medication among uninsured or low-income Utah residents along with flat federal funding have caused the program to run out of money for new patients. Current aid recipients will continue to receive assistance. The health department encourages individuals who cannot afford medications to seek aid from pharmaceutical companies. For more information, please see the related article in the Salt Lake Tribune.

Napo Sues Salix Over HIV-Associated Diarrhea Drug – Napo Pharmaceuticals is suing Salix Pharmaceuticals for breaching a contract to develop the prospective diarrhea drug crofelemer for use in people with HIV. In the suit, Napo contends that Salix, which licensed the drug from Napo, has failed to adequately pursue FDA approval; representatives from Napo have stated that they wish to terminate the contract. Salix contends that the lawsuit has no merit and that it will continue to develop the drug and market it as planned. For more information, please see the related article in Medcity News.

May 19 Marks National Asian And Pacific Islander HIV/AIDS Awareness Day – On May 19, the Banyan Tree Project will lead activities to commemorate Asian and Pacific Islander HIV/AIDS Awareness Day and to decrease the stigma surrounding HIV and AIDS in Asian and Pacific Islander communities. Asian and Pacific Islanders constitute approximately 1 percent of HIV-positive individuals in the United States. Organizations that support HIV and AIDS causes in Asian and Pacific Islander communities will be hosting events to raise awareness across the country. For more information, please see the AIDS.gov website.

New York State Department Of Health Releases Guidelines On Prevention Of Secondary HIV Transmission – The New York State Department of Health AIDS Institute has released guidelines for the prevention of secondary HIV transmission, titled “Prevention with Positives: Integrating HIV Prevention into HIV Primary Care.” The guidelines recommend that people with HIV undergo sexual risk assessments every three to four months. They also suggest that health care providers discuss risk reduction strategies with their patients on an individualized basis. People with HIV should be screened annually for sexually transmitted infections and educated about HIV viral load (amount of HIV in the blood), transmission risk, and safe sex practices. Additionally, health care providers should review substance abuse history with each patient and discuss avoiding syringe or needle sharing with all injection drug users. For more information, please see the New York AIDS Institute website.

FDA Approves New Human Papillomavirus Test For Cervical Cancer Screening In Women – Roche announced last week that the U.S. Food and Drug Administration (FDA) has approved its cobas Human Papillomavirus (HPV) test, which screens women for the two HPV strains most commonly associated with cervical cancer. The approval was based on a clinical trial in 47,000 women that showed that 10 percent of women who tested positive for HPV strains 16 or 18 had pre-cervical cancer, even though they had normal Pap smear results. Most women with HIV (75 to 80 percent) also have HPV, and women with HIV are at higher risk of cervical cancer (see related AIDS Beacon news); studies estimate that 20 to 60 percent of women with HIV have signs of pre-cervical cancer. The new test is designed for use in addition to a routine Pap smear. For more information, please see the Roche press release.

AIDS Patients May Have A Higher Risk Of Developing Stomach And Esophageal Cancers – Results of a recent study suggest that AIDS patients have a higher risk of developing stomach and esophageal cancers. Scientists at the National Cancer Institute analyzed data from nearly 600,000 AIDS patients. Of those, 1,666 developed stomach cancers, while 240 developed esophageal cancers. Patients with AIDS had a nearly seven-fold greater chance of developing stomach cancer and an almost three-fold greater chance of developing esophageal cancer when compared to the general population. The results were presented last week at the American Association for Cancer Research (AACR) 102nd Annual Meeting. For more information please see the AACR News website or abstract 3744 from the conference.

Risk Of HIV Transmission Can Be Predicted By Virus Levels In Genital Secretions – A study published last week indicates that the levels of HIV in genital secretions,  independently of those in the blood, indicate the risk of transmitting HIV between heterosexual partners. Participants with higher levels of virus in their genital secretions were more likely to transmit HIV, regardless of their viral load (amount of HIV in the blood). The authors stated that the results help scientists better understand when transmission risk is greatest, which could help with HIV prevention technologies and methods. For more information, please see the news article at U.S. News and World Report or the study in Science Translational Medicine (abstract).

GlaxoSmithKline Is Recruiting Participants For Clinical Trial For New Therapeutic HIV Vaccine – GlaxoSmithKline (GSK) is currently recruiting participants for a new Phase 2 clinical trial to study whether its investigational therapeutic HIV vaccine, GSK Biologicals HIV Vaccine 732462, can lower viral loads and delay the need for treatment in treatment-naïve HIV-positive adults. Therapeutic HIV vaccines are meant to help the immune system fight HIV in people who are already HIV positive. Eligible participants must have a viral load between 2,000 and 80,000 copies per milliliter of blood. The study will compare the safety and efficacy of the vaccine to a placebo. For more information, please see the U.S. Clinical Trials Registry.

Based on these results, the researchers recommended that personal lubricants undergo more rigorous safety testing, particularly with regard to their effects on transmission of HIV and other sexually transmitted diseases.

The investigators noted that since these results were found in laboratory experiments, further studies are needed to determine the effects of these lubricants in humans.

“What happens in the laboratory environment does not always happen in the human body. In fact, lubricants generally appear to play an important role in preventing the spread of HIV,” said Dr. José Fernandez-Romero, senior investigator of the study.

“Intercourse without them can damage cells, which could promote HIV transmission. Condom-safe lubricants also may reduce the likelihood that a condom will break. But we need to know more,” he added.

Despite the fact that personal lubricants are commonly used during vaginal and anal intercourse, the effects of these products on the transmission of HIV and other sexually transmitted infections have not been thoroughly studied.

However, some recent studies have suggested that some lubricants are active against HIV and may potentially prevent the sexual transmission of HIV.

In this study, researchers at Duke University and the Population Council, a non-profit organization that focuses on reproductive health, investigated the anti-HIV activity of 41 personal lubricants in a human cell line commonly used to measure HIV replication rates.

The results of the study showed that none of the lubricants tested had anti-HIV activity.

However, four of the lubricants examined increased HIV replication in the cell line: Astroglide Liquid, Astroglide Warming Liquid, Astroglide Glycerin & Paraben-Free Liquid, and Astroglide Silken Secret.

All four lubricants shared a common ingredient called polyquaternium. Three of the lubricants had polyquaternium-15.

The researchers looked at a related polyquaternium compound and confirmed that it increased HIV replication in laboratory experiments.

Additionally, these four lubricants and a majority of the other lubricants tested were found to cause damage to a human epithelial cell line taken from the colon.

Epithelial cells line the vagina and rectum and help protect the cells underneath them that are susceptible to HIV infection; damage to epithelial cells can provide a passageway for HIV to enter the body.

The investigators suggested that injuries induced by the use of these lubricants could potentially enhance HIV transmission.

For more information, please see the article in AIDS Research and Human Retroviruses (pdf).

The researchers concluded that transmitted drug resistance is still a problem and emphasized the need for early diagnosis and aggressive treatment strategies for people with drug-resistant HIV.

HIV that is resistant to treatment with antiretrovirals is one of the most common reasons that treatments fail. When people with drug-resistant HIV pass their virus on to others, those newly infected people have fewer treatment options.

Drug-resistant HIV is usually transmitted by people who are undergoing antiretroviral therapy but fail to achieve viral suppression (an undetectable amount of HIV in the bloodstream), or by people who acquire drug-resistant HIV and transmit it before beginning antiretroviral therapy.

As more and more HIV-positive people take antiretroviral drugs for longer lengths of time, the prevalence of drug-resistant HIV has increasingly become a cause for concern. In many areas, 10 percent to 20 percent of new HIV infections involve transmission of drug-resistant HIV.

Beginning in late 2007, new HIV medications including Isentress (raltegravir), Selzentry (maraviroc), and Intelence (etravirine) were introduced.

Researchers predicted that these newer antiretrovirals would better suppress transmission of drug-resistant forms of HIV if the main driver was transmission by people on antiretroviral therapy, since the new drugs would be better at suppressing HIV that is resistant to older medications.

Conversely, researchers hypothesized that if the main driver of transmitted drug resistance was treatment-naïve people with drug-resistant HIV, the impact of improved antiretroviral therapy would be minimal or delayed until the new drugs become widely available.

In this study, the researchers tried to determine whether the new antiretrovirals had an effect on transmission rates for drug-resistant HIV in the years since they were approved. To do so, they used results from a study that was designed to measure rates of transmitted drug resistance between 2002 and 2009.

The study included 372 people in San Francisco who had tested positive for HIV within 12 months of enrollment. Most of the participants (96 percent) were men who have sex with men; 9 percent of participants were injection drug users.

Participants were divided into two groups: those who tested positive for HIV between 2005 and 2007 and those who tested positive between 2008 and 2009. This allowed researchers to compare the prevalence of transmitted drug resistance before and after the introduction of new antiretrovirals in late 2007.

The researchers analyzed participants’ CD4 cell counts, viral load, and the presence of any drug resistance mutations displayed by their HIV.

Results showed that the prevalence of transmitted drug resistance more than tripled between 2003 and 2007 from 7 percent in 2003 to 24 percent in 2007. Between 2008 and 2009, the rate dropped to 15 percent of participants.

However, the researchers concluded that the difference was not statistically significant, and that overall, the chances of acquiring drug-resistant HIV in 2008 to 2009 were not significantly lower than the chances of acquiring drug-resistant HIV in 2005 to 2007.

The researchers listed two possible explanations for the study results: (1) poor antiretroviral therapy adherence and/or poor medical care in people who are on antiretroviral therapy or (2) considerable transmission of drug resistance via treatment-naïve individuals. Since other studies have indicated that more HIV-positive people in San Francisco have successfully achieved viral suppression in recent years, the researchers thought the second explanation was more likely.

The study authors stressed that there is a scarcity of data on the use of new antiretroviral medications in San Francisco and warned that delayed uptake of the new drugs will have a delayed impact on transmission of drug-resistant HIV.

As a result, they suggested that longer studies with participants from broader geographic areas are needed to allow for better comparisons of transmitted drug resistance rates before and after the introduction of novel anti-HIV drugs.

For more information, please see the study in PLoS One.