University of California, San Francisco researchers and Brazilian colleagues report that analysis of blood samples taken at an anonymous test site in Santos, Brazil from 1995 to 1999 show an increase in the rate of HIV infection after a period of decline.
The increase was noted particularly in heterosexual women, a group that has not previously had a high rate of HIV infection in this area.
A preliminary analysis of a small number of blood samples also found evidence of transmission of a drug-resistant virus strain, said Kimberly Page-Shafer, PhD, MPH, UCSF assistant professor of medicine and epidemiologist with the UCSF Center for AIDS Prevention Studies.
Page-Shafer presented the findings today (July 13) at the XIII International AIDS Conference in Durban, South Africa.
The port city of Santos has been an epicenter of the AIDS epidemic in Brazil, and offers an excellent system of testing and treatment, according to Page-Shafer. Previous analysis of the epidemic had shown a high rate of HIV infection in men who have sex with men and in IV drug users, and well directed education and prevention efforts have been targeted at these groups.
In Santos, and throughout Brazil, antiretroviral treatment is available free of charge to anyone who is HIV positive, said Page-Shafer.
"The widespread availability of antiretroviral therapy has been a tremendous public health service to the population. At the same time, however, there has been some concern that inadequate adherence to medications might lead to the development of drug-resistant viral strains," said Page-Shafer.
The study used a new test, developed at the Blood Centers of the Pacific in San Francisco and the Centers for Disease Control and Prevention (CDC), that can distinguish recent infections from long-standing ones. It allows researchers to identify individuals who have become infected within the past 4 to 6 months. This study is one of the first applications of this sensitive test to surveillance activities outside of the United States.
"The new test is very valuable because surveillance and prevention have been difficult without a way to distinguish recent infections. This test provides a tool that allows us to precisely identify where transmission is occurring now, and target prevention efforts accordingly," said Page-Shafer.
Researchers used the test on HIV-positive frozen blood samples drawn at an anonymous counseling and testing site in Santos for the four-year period 1995-99. Of 392 HIV positive frozen samples, 44 (11 percent) were found to be recent infections.
The researchers then looked more closely at the 18 recent infections that occurred in 1999. In this group, 76 percent were women, most of whom reported one sex partner within the past year. Recently infected individuals were also more likely to report anal sex and a history of sexually transmitted disease. Overall, the researchers calculated the annual incidence of HIV infection (number of new cases per 100 people per year) to be 1.9 percent in 1995, 1.5 percent in 1996, 1.3 percent in 1997, 2.4 percent in 1998, and 3.2 percent in 1999.
"The increase in the rate of HIV infection in the last two years of the study is cause for concern," said Page-Shafer.
Researchers are still in the process of analyzing a small number of recent-infection blood samples to see if the virus they contain is resistant to antiviral drugs. So far, they have found one of five samples to be resistant to azidothymidine (AZT).
"The evidence of transmission of antiretroviral-resistant virus points strongly to the need for further efforts to monitor this phenomenon in Brazil," said Page-Shafer.
Research co-investigators included Katia Alves, MD, infectious disease specialist and Fogarty Fellow at UC Berkeley and the Blood Centers of the Pacific; Bhupat Rawal, PhD, also from the Blood Centers of the Pacific; Marcos Caseiro, MD, director of the Central AIDS Clinic (CRAIDS)in Santos, Brazil, who is associated with Federal University of San Paulo (UNIFESP); Ricardo Diaz, MD, director of the Retrovirology Laboratory at UNIFESP; Cecilia Sucupira, a research scientist at UNIFESP; Hugo Guevara, PhD, and Mike Hendry, PhD, microbiologists with the Department of Health Sciences Viral and Ricketssial Disease Laboratory; Alison Graves, MPH, research assistant with the UCSF Center for AIDS Prevention Studies (CAPS); George Rutherford, MD, director of the CAPS International Program; and Thomas J. Coates, PhD, executive director of the UCSF AIDS Research Institute and CAPS.