Nucleic acid testing can boost number of HIV infections detected in the community

Michael Carter
Published: 18 June 2010

Nucleic acid testing increased the number of HIV infections detected by a community testing programme by almost a quarter, US investigators report in the Annals of Internal Medicine.

“This study should motivate further research into the use of nucleic acid testing in HIV testing programs with measurement of cost-effectiveness and prevention of HIV transmission,” comment the investigators.

Donated blood samples in the United States are already routinely screened for HIV using nucleic acid testing. This technology is able to detect very early HIV infections.

Investigators from the Early Test project in San Diego, California, wished to see if the use of non-pooled nucleic acid testing would increase the number of HIV infections detected by community screening. A possible advantage of non-pooled nucleic acid testing in the community is its ability to detect acute HIV infections. Individuals in this phase of HIV infection are often highly infectious, and some research suggests that they make a disproportionately large contribution to the continued spread of HIV.

All the patients in the study had a rapid, oral HIV test, and blood samples were drawn from both those testing HIV-positive and HIV-negative for further analysis, with all negative samples screened using nucleic acid testing.

The investigators also wished to evaluate the uptake of an automated service for the provision of negative test results.

Between early 2007 and January 2009, a total of 3151 individuals were tested for HIV. Of the 2563 men taking part in the study, a total of 1774 were gay and other men who have sex with men.

Overall, 79 individuals (3%) were newly diagnosed with HIV.

A total of 15 (19% of all those with HIV) did not have antibodies to HIV, and they were only diagnosed because of the use of nucleic acid testing.

The investigators calculated that the use of non-pooled nucleic acid testing increased the yield of newly diagnosed infections by 23%.

Median viral load amongst these 15 individuals was 127,000 copies/ml. But this varied considerably, from below 50 copies/ml to over 7,400,000 copies/ml.

One individual whose infection was detected by nucleic acid testing initially had an undetectable viral load, but this had increased to millions of copies within a week.

Gay and other men who have sex with men had the highest overall rate of HIV infection (4%).

In the investigators’ first set of analyses, acute or early HIV infection (positive antibody result, detuned EIA) was significantly associated with recent diagnosis with syphilis (p = 0.044), and having ten or more sexual partners in the previous twelve months (p = 0.031).

Having a large number of sex partners remained significant in subsequent analysis (OR = 2.8; 95% CI, 1.0 to 7.8).

The investigators calculated that the estimated additional cost to the screening programme of each additional HIV infection detected using nucleic acid testing was $10,258.

Internet and voicemail results service

Of the 3070 individuals who were negative, 2105 (69%) accessed their test results using the internet or an automated voicemail system.

Individuals using these methods appeared to be more socially advantaged and to have fewer risk behaviours. They were more likely to be gay or other men who have sex with men, had higher incomes, were of younger age, but less likely to have had recent infection with syphilis or to have used methamphetamine.

All individuals whose nucleic acid result was positive were directly contacted, most within 24 hours. All were referred to specialist HIV care and attended their first clinic appointment.

A total of 235 patients completed an internet survey about their satisfaction with the testing programme.

Almost all (232, 99%) said that it was “very important” to have testing available that could detect acute HIV infections, and 69% reported that they had referred somebody else to the service.

A role for nucleic acid testing in community testing programmes?

“Between February 2007 and January 2009, the Early Test program found 15 cases of HIV infection that would have been missed by HIV antibody testing alone, increasing case yield by 23%,” comment the investigators.

The investigators believe that nucleic acid testing has advantages over the fourth-generation assays currently in use.

Fourth-generation assays use both antibody tests and an assay to detect p24 antigen. It is estimated that they can identify 62 to 94% of acute infections.

However, these assays can miss some very early infections that nucleic acid testing would detect. Indeed, the investigators believe that fourth-generation tests would not have diagnosed a number of infections picked up in their study where the patient had a low or undetectable viral load.

Reference

Morris SR et al. Evaluation of an HIV nucleic acid testing program with automated internet and voicemail systems to deliver results. Ann Intern Med 152: 778-85, 2010.

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