JAC Advance Access originally published online on September 23, 2009
Journal of Antimicrobial Chemotherapy 2009 64(6):1126-1129; doi:10.1093/jac/dkp353
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Leading articles |
Dried blood spots can expand access to virological monitoring of HIV treatment in resource-limited settings
1 Ulleval Department of Infectious Diseases, Oslo University Hospital, Oslo, Norway 2 Ulleval Medical Department, Oslo University Hospital, Oslo, Norway 3 HIV Unit, Geneva University Hospital, Geneva, Switzerland 4 Campaign for Access to Essential Medicines, Médecins sans Frontières, Geneva, Switzerland
* Corresponding author. Tel: +47-97983264; Fax: +47-22119181; E-mail: asgeir.johannessen{at}medisin.uio.no
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Abstract |
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Top
Abstract
The challenge: treating HIV/AIDS...The global scale-up of antiretroviral treatment in past years has, unfortunately, not been accompanied by adequate strengthening of laboratory capacity. Monitoring of treatment with HIV viral load and resistance testing, as recommended in industrialized countries, is rarely available in resource-limited settings due to high costs and stringent requirements for storage and transport of plasma. Consequently, treatment failure usually passes unnoticed until severe symptoms occur, when resistance mutations have accumulated and second-line drug options are restricted. Dried blood spots (DBS) are easy to collect and store, and can be a convenient alternative to plasma. Recently, a number of studies have demonstrated the feasibility and reliability of using DBS to monitor viral load and genotypic resistance. Moreover, several African countries have already started to use DBS for paediatric HIV screening. In the absence of point-of-care assays, the WHO should encourage virological monitoring on DBS in antiretroviral treatment programmes in resource-limited settings.
Keywords: HIV infections , antiretroviral therapy , drug resistance
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The challenge: treating HIV/AIDS where there is limited laboratory capacity |
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Immense efforts and resources have been put into the global scale-up of antiretroviral treatment (ART) in resource-limited settings in past years. By the end of 2007, 3 million people were receiving ART in low- and middle-income countries, which is a >10-fold increase since 2002.1 Price reductions on antiretroviral drugs from more than US$10 000 to less than US$100 per person per year have been instrumental in the campaign for universal access to ART.2 Unfortunately, the rollout of treatment programmes has not been accompanied by a similar strengthening of laboratory capacity (Figure 1). While prices for antiretroviral drugs have decreased dramatically due to generic competition, the costs of laboratory equipment needed to monitor treatment have remained high.
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The honeymoon for global scale-up is over. Early treatment success has been reported from ART programmes in many low-income countries, but to uphold the success will demand a sustained effort from donor agencies as well as local ministries of health. Until now the main focus has been on quantity, such as the ‘3 by 5’ initiative from the World Health Organization (WHO), which aimed for 3 million people on ART by 2005, and more recently the goal of universal access by 2010. However, as more and more patients are receiving ART worldwide, the focus must shift from rapid scale-up to quality-assured scale-up and ensuring long-term success of therapy.
In high-income countries, monitoring of ART with viral load and genotypic resistance testing are considered mandatory elements of patient care, in order to determine when treatment fails and tailor new regimens in failing patients.3 These tests, however, are expensive and technically complex, and remain unavailable to the vast majority of HIV-infected individuals globally. Thus, clinicians in low-income countries are often left virtually blindfolded in the assessment of treatment failure, the need for second-line therapy and HIV status in infants.
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Dried blood spots: a long-standing experience |
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In the absence of low-tech point-of-care assays for virological monitoring, an alternative strategy could be the shipment of specimens from peripheral clinics to central laboratories. However, stringent requirements for storage and transport of plasma are barriers in settings with a limited infrastructure. Dried blood spots (DBS) can be an alternative to plasma samples, and have been used for >40 years to screen for metabolic disorders in neonates.4 DBS specimens are collected by spotting whole blood onto filter paper (Figure 2), either from venous blood or directly from a finger prick, making this method particularly suitable in rural settings. Furthermore, DBS packed in zip-lock plastic bags with desiccant can be stored and shipped at ambient temperature, thus avoiding the need for cold chain and speedy transport to the laboratory.5 The consumable costs for DBS are less than US$1 per test, and transport costs are markedly reduced compared with plasma, although the actual assay costs remain unchanged, and the extraction of nucleic acids from DBS involves some extra hands-on time at the central laboratory.6,7
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Viral load quantification using DBS |
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Viral load measurements are mainly used to monitor the efficacy of antiretroviral therapy. When viral loads are unavailable, the WHO recommends that treatment failure should be assessed by clinical signs or CD4 cell counts.8 However, clinical symptoms and CD4 decline have poor sensitivity and specificity in detecting virological failure.9 Hence, patients with adequate virological suppression risk undergoing a premature switch to costly and complex second-line therapy. Furthermore, patients with actual treatment failure risk not being detected until they develop severe clinical symptoms, and prolonged exposure to a failing ART regimen leads to accumulation of resistance mutations, thus jeopardizing future treatment options.
Standard viral load assays are based on nucleic acid amplification of HIV-1 RNA. These assays are complex, expensive and require electricity, air conditioning and clean water, which usually limit their use to larger hospitals in capital cities or research projects. Newer assays based on real-time PCR or nucleic acid sequence-based amplification (NASBA) technology, although less expensive, have the same limitations. An alternative enzyme-linked immunosorbent assay (ELISA)-based assay exists, which measures reverse transcriptase activity (ExaVir Load; Cavidi AB, Uppsala, Sweden). However, this assay is time-consuming, involves several steps and the cost is still high. A dipstick PCR assay is under development by a research group at Cambridge University,10 but this assay is not yet commercially available.
Several studies from North America and Europe have shown that DBS can be used to reliably measure viral load.5,11–13 More recently, our own work in rural Tanzania has demonstrated the feasibility and reliability of using DBS for viral load monitoring under basic field conditions.14 Indeed, we found that DBS, in combination with the NucliSENS EasyQ HIV-1 assay (BioMérieux, Inc., Madrid, Spain), had a sensitivity of 91% and a specificity of 97% in detecting major virological failure, defined as a plasma viral load of 
5000 copies/mL. DBS have also been evaluated for non-B subtypes showing consistently satisfactory results.14–16
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Drug resistance testing using DBS |
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Genotypic resistance testing is mainly used in patients who experience treatment failure, in order to tailor a new fully active regimen.3 With an increasing number of patients receiving ART for years in resource-limited settings, the need for resistance testing, at a public health level and at an individual level for selected cases, can no longer be neglected. Switching blindly to a new regimen will become virtually impossible when patients need third- and fourth-line ART. Genotypic resistance testing is complex and expensive, and requires advanced laboratories with PCR capacity, limiting its use to major cities. Ideally, a low-tech point-of-care test should be developed, and an acceptable alternative could be a simplified assay only for selected signature mutations.
Recently, several studies have evaluated the use of DBS for drug resistance testing. In a study on HIV subtype B-infected individuals from Spain, all 46 DBS specimens from patients with a viral load of 500 copies/mL were successfully amplified using the commercial ViroSeq assay (Abbott Molecular, Des Plains, IL, USA).17 Other studies have found amplification rates of 90.1%–92.5% in DBS specimens from Mexico and Cameroon using in-house PCR assays.18,19 A study using the commercial Trugene HIV-1 Genotyping Kit (Siemens Medical Solutions Diagnostics, Tarrytown, NY, USA) reported successful amplification in 78.8% of DBS specimens.20 All these studies found a high concordance between resistance mutations in plasma and DBS, and an overall nucleotide similarity ranging from 98.1% to 99.95%. Our own experiences with the use of DBS in rural Tanzania support these findings; >90% of DBS specimens from patients with virological failure were successfully amplified, and there was good agreement with mutations found in plasma.21
The WHO, in collaboration with a network of international experts (HIVResNet), recently published a laboratory strategy for surveillance of HIV drug resistance, where the use of DBS was recommended in resource-limited settings.22 This method was successfully employed in surveys of transmitted resistance in Tanzania and Malawi.23,24 However, until now, the WHO has only focused on the role of DBS in public health surveillance, and not in the clinical management of individual patients.
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DBS as a tool for HIV screening in neonates |
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HIV-infected infants represent a particular concern with regard to diagnosis, treatment and monitoring. A major obstacle to paediatric ART is the difficulty of diagnosing HIV in infants. The persistence of maternal anti-HIV antibodies until 12–18 months of age precludes the use of rapid antibody tests, and the cost and complexity of PCR assays limit their use in resource-limited settings.25
Recently, several African countries have started to use DBS in order to expand the accessibility of HIV testing for infants exposed to vertical HIV transmission.26 Detection of HIV-1 DNA in DBS is a highly sensitive and specific test of HIV infection in infants,27 and early diagnosis and treatment is key to reducing mortality in this age group.28 Hence, the use of DBS is already familiar to healthcare providers and laboratory technicians in several low-income countries, and this can serve as a model for further expansion of DBS monitoring strategies in such settings. Nonetheless, most HIV-exposed infants worldwide still lack access to a reliable HIV screening test, and without treatment more than one-third of HIV-infected children will not survive past their first birthday.25
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Limitations of DBS in HIV monitoring |
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The use of DBS is not without caveats. First, the small amount of blood in a dried spot gives a reduced sensitivity in detecting HIV-1 RNA when the viral burden is low (<1000–4000 copies/mL).5,13,14 On the other hand, in the updated 2006 guidelines, the WHO recommends conservation of first-line ART in resource-limited settings as long as viral load does not exceed 10 000 copies/mL.8 We believe, therefore, that in the absence of evidence to support regimen switching at <1000 copies/mL, DBS are sufficiently sensitive to decide who needs second-line ART in such settings.
Second, since DBS consist of whole blood instead of plasma, cell-associated proviral DNA can contribute to the end product. This can explain why some studies have found false-positive viral load results in DBS.29,30 However, this problem can be overcome by using a viral load assay based on NASBA technology, like the NucliSENS EasyQ HIV-1 assay (BioMérieux, Inc.), which is an isothermal transcription-based amplification system designed specifically for RNA detection.31,32 With regard to resistance testing, it has been shown that proviral DNA may affect results by contributing historically archived sequences.33,34 Nevertheless, most studies have found good agreement between genotypes generated from plasma and DBS.17–21
Third, adequate storage conditions for DBS have yet to be established. For viral load quantification, some studies suggest a significant loss of HIV-1 RNA after 1–3 months storage at room temperature.11,15 In contrast, a multicenter study from North America found stable HIV-1 RNA levels in DBS stored at room temperature for at least 1 year.5 With regard to resistance testing, recent studies showed that genotyping was highly efficient in DBS stored at 4°C for 1 year,35 although storage at extreme conditions (37°C and 100% humidity) resulted in a rapid decline in the efficiency of genotyping after just 2 weeks.36 For clinical monitoring of patients on ART, monthly shipment of DBS to a reference laboratory would probably be appropriate, both to avoid degradation of HIV-1 RNA, and to assure a timely switch to second-line ART in case of treatment failure.
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Steps to action |
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There is an urgent need for virological monitoring tools developed specifically to operate under basic field conditions in resource-limited settings. Ideally, an affordable, simple and robust point-of-care assay should be developed. Donor agencies, decision-makers and the laboratory industry have a responsibility to invest in the development of laboratory equipment for low-income countries, in order to ensure the long-term success of ART worldwide.
Unfortunately, field-adapted tools for virological monitoring are not yet available. In the meantime, a monitoring strategy based on DBS is the only viable option and should be included in the next revision of the WHO guidelines, in order to meet the growing need for viral load, genotypic resistance and infant diagnosis testing in resource-limited settings. Otherwise the tremendous gains in HIV treatment in past years might be lost in the coming decade.
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Transparency declarations |
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We declare that we have no conflicts of interest.
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References |
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35
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36
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