Big increase in number of Americans infected with drug resistant HIV

The number of Americans being infected with a drug resistant strain of HIV is increasing, according to a study published in the 8 August 2002 edition of the New England Journal of Medicine.

Investigators conducted a retrospective analysis of the medical records of 377 people with primary HIV infection and no previous HAART use, in ten US cities between 1995 and 2000.

Over 76% of the people in the trial were white gay men who presented to a participating clinic with acute retroviral syndrome after an episode of high risk sex. Sharing injecting equipment was reported by 12% of study participants and unprotected sex and injecting drug use by 11%.

Baseline tests revealed that the people in the study had a median CD4 count of 489 cells and a viral load of 4.8 log. Tests to assess the susceptibility of the trial participants to antiretroviral drugs were performed on average 71 days after HIV infection. Investigators looked for three separate drug-susceptibility thresholds (phenotypic testing) in order to ensure that the spectrum of different resistant patterns which emerge in response to antiretroviral drugs were detected, as well as sequencing for genotype.

The investigators established that the frequency of high-level phenotypic resistance to one or more anti-HIV drugs increased from 3.4% in 1995-1998 to 12.4% in 1999 and 2000, and that the frequency of multi-drug resistance increased from 1.1% to 6.2% by 1999-2000.

The investigators also found that in the people infected with a drug resistant strain of virus, it took up to 33 days longer to achieve an undetectable viral load than it did for those with fully drug susceptible HIV. In addition, viral load rebounded more quickly in people treated with HAART who were initially infected with drug resistant HIV. It should however be stressed that these differences were only just judged to be statistically significant (P=0.05 for both comparisons), and as the study sample was relatively small, some researchers may be tempted to treat these findings with caution until they are supported by a larger investigation.

Wider use of HAART is believed by the investigators to be the reason for the large increase in transmitted drug resistance between 1998 and 1999–2000. However, the study also notes that there have been reports of "increasing rates of unsafe sex" amongst gay men and that this could lead to "increased frequency of drug resistance".

The value of testing for HIV shortly after exposure to the virus is stressed by the study authors, who note that "identification of patients early after the acquisition of HIV infection may facilitate the identification of transmitted drug resistance and improve the selection of more effective first-line therapies."

The study concludes that as many people are now infected with drug resistant virus, "guidelines for empirical treatment can no longer be relied on for newly infected patients... the treatment strategies for patients newly infected with HIV should take into account the prevalence of transmitted drug resistance."

The NAM booklet Resistance in the information for HIV-positive people series, provides useful information on how resistance to anti-HIV treatments occurs, and how it can affect therapy.