Standard tests for HIV, the virus that causes AIDS, can't identify people very recently infected with the virus, but a more sensitive test can, new research shows.

By testing for HIV's genetic material in addition to antibodies against the virus in more than 3,000 people, Dr. Sheldon R. Morris of the University of California San Diego and colleagues identified 15 HIV-infected patients who the standard test would have missed.

In the first few days after becoming infected with HIV a person has extremely high amounts of HIV in the blood, meaning he or she can transmit the virus to others much more readily, Morris and his team note. Blood banks screen donors for HIV with nucleic acid testing, or checking for the building blocks of the virus's genetic material; this approach can identify an HIV-positive person about 12 days before that person begins making antibodies against the virus.

In the new study, the investigators looked at whether the genetic material test could identify more newly infected individuals than the current standard rapid tests. They tested more than 3,100 people seeking HIV testing at sites in San Diego County using both the nucleic acid test and the rapid test. Seventy-nine people had HIV infection, 15 of whom had tested positive with the nucleic acid test but were negative with the rapid test.

Morris and his colleagues also offered study participants the opportunity to check their results by voice mail or online. Those who tested positive with the rapid test were told on-site, while those who tested negative were told that if the more sensitive test identified HIV infection, they would be contacted within two weeks. Study participants who did not hear from clinic staff by then could call a voicemail number or log on to a confidential Web site to get their results.

Sixty-nine percent of the study participants who tested negative accessed their results through voice mail or the Internet, with about two-thirds of these individuals opting for the Internet.

According to the investigators, it cost about $160,000 to set up the program, including the voice mail and Internet notification system, for a total of about $10,000 for each additional HIV infection identified. While they didn't do a "cost-effectiveness" analysis, Morris said the spending is well in line, and likely below, many other interventions in wide use such as breast cancer screening.

State regulations currently control how people get their results after HIV testing, Morris noted. For people who undergo HIV testing frequently, and have already received counseling, he added, getting negative results automatically could make the process less onerous. "You could see for some people that convenience factor would be a plus to them, especially the people who are used to the system," Morris said.

"There's not that much infrastructure that really needs to be built to allow that," he added. "Once you've got that working, it pays for itself, obviously."

The study was supported by funding from the California HIV/AIDS Research Program and the National Institutes of Health.