Categorisation of transmitted HIV drug resistance using the WHO/CDC HIV drug resistance threshold survey method may be useful in resource limited settings

Polly Clayden, HIV i-Base

Widespread HIV drug resistance is of great concern in settings where antiretroviral treatment is being rapidly scaled up, particularly when access to regimens is limited.

In order to evaluate transmitted HIV drug resistance (HIVDR) in resource-limited settings, the World Health Organisation (WHO) and the Centers for Disease Control and Prevention have developed a low resource strategy, the HIVDR threshold survey (TS), based on a sequential sampling method.

This method was developed for use in specific geographical areas of resource-limited countries where transmitted HIVDR is likely to be seen first. It categorises the prevalence of transmitted HIVDR for each relevant antiretroviral drug and class of drug as <5%, 5–15%, or >15%, based on 47 specimens from people recently diagnosed with HIV. It was developed using computer simulations based on a million HIVDR results generated from expected distributions and 1797 actual HIVDR results from 28 clinical centres.

The investigators compared TS categorisations with HIVDR prevalence estimates from surveys of recently infected individuals in two areas where previous studies showed >20% transmitted HIVDR. Genotyping was performed on samples from 367 people with diagnosed with HIV between 2003 and 2005 at 27 sites in Los Angeles and 268 people at 23 sites in Chicago. All were subtype B. Prevalence was estimated based on results from all recently infected participants identified by a less-sensitive enzyme immunoassay (LS-EIA). For the TS categorisations, analyses were restricted to the first 47 HIV-positive eligible samples from each area.

Based on the LS-EIA, 73 samples were eligible from Chicago and 66 from LA. The prevalence of transmitted HIVDR to one or more drug in any class in Chicago was 24.7% (NRTIs: 15.1%; NNRTIs: 12.3%; PIs: 2.7%); and 19.7% in LA (NRTIs: 13.6%, NNRTIs: 10.6%, PIs: 1.5%). The TS categorisations for Chicago were: overall HIVDR: >15%, NRTIs: >15%, NNRTIs: 5–15%, PIs: <5%. And for LA, the TS categorisations were: overall HIVDR: >15%, NRTIs: 5–15%, NNRTIs: 5–15%, PIs: <5%.

They reported that in these two areas of high prevalence of transmitted HIVDR, the analysis based on the first 47 samples correctly categorised the prevalence estimates based on the larger number of samples. They suggested that the TS method may make HIVDR surveillance feasible in resource limited settings, where people are rarely diagnosed in recent infection.

As this method focuses on areas where HIV drug resistance is most likely to be transmitted first, it could support plans for appropriate public health interventions. They wrote, “Separately categorising transmitted HIVDR prevalence in specific geographic areas also avoids basing conclusions about a ‘national’ prevalence of transmitted HIVDR on results from a few sites.”


Bennett DE, Smith A, McCormick L et al. Categorisation of transmitted HIV drug resistance using the WHO/CDC HIV drug resistance threshold survey method. XV International HIV Drug Resistance Workshop, Sitges, Spain, July 2006. Abstract 103.

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