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San Francisco Serosorting May Explain Odd HIV Data: STDs Have Risen, butNot New HIV Infections; Internet Sex Apparently Not Issue
  AIDS Alert
May 1, 2004
Vol. 19, No. 5, P. 55
CDC HIV/STD/TB Prevention News Update
Documented increases in STDs among high-risk populations in SanFrancisco, including men who have sex with men (MSM) who use the Internet tofind anonymous sex partners, did not lead to a widely expected synergeticrise in HIV incidence. In fact, using a detuned assay test, the same publichealth officials and researchers who uncovered the syphilis increase amongMSM found that HIV incidence was leveling off for the past several yearsdespite the STD increases.
Health officials also found that safe sex behavior increased since 1998among HIV-negative MSM who reported having sex with an HIV-positive partner.So while sexual risk behavior is increasing, MSM are having sex withpartners whom they know have the same serostatus, investigators concluded.One hypothesis is that MSM are serosorting through the Internet - the samevenue that makes it more likely they will increase their sexual riskbehaviors.
"If persons who are the same HIV serostatus are in the same networks sothat positives are having unprotected sex with positives and negatives withnegatives, then you could see an increase in syphilis transmission withoutan increase in HIV transmission," noted Willi McFarland, MD, PhD, directorof HIV/AIDS Statistics and Epidemiology for the San Francisco Department ofPublic Health.
In addition, data collected by a Stop AIDS Project survey showed thatfrom 2001 on, HIV-positive MSM were saying they knew their partner'sserostatus, said McFarland. And HIV-negative MSM reported knowing theirpartner's serostatus in more recent years. The survey found people who wereHIV-positive were having fewer partners they knew to be HIV-negative.
Though hard data are lacking, it is possible that the leveling off ofHIV cases could be due to the city's prevention-for-positives campaign. Thateffort began in 2001 with media saturation featuring celebrities, andphysicians trained to provide prevention in HIV care clinics, saidMcFarland. Additional research is needed to further test the hypothesis anddiscover how serosorting works. On the Internet, "people put in theirserostatus and say they're looking for someone with the same serostatus, andwe know that partnering on the Internet is becoming more common," he said.
"Part of me worries that this may be a little too optimistic," saidMcFarland. "It's a lot to ask that people know their own serostatus and askpartners about them." Serosorting depends on people knowing their status ifthey're positive and remaining negative if they're not, and then beinghonest about their status when negotiating sexual encounters, he said.
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