The importance of nucleic add testing (NAT) has become increasingly evident during the last decade for many purposes such as screening and diagnosis of infectious diseases and genetic disorders, testing for disease susceptibility, therapy monitoring, and improving the safety of blood supplies. NAT combines the advantages of direct and highly sequence-specific detection of the genome of an infectious agent with an analytic sensitivity that is several orders of magnitude greater than that of immune-based tests, or virus isolation and self culture methods. Due to the high sensitivity of NAT, its use in blood banks reduces the risk of infectious agent transmission during the period between infection and seroconversion, of infection with immunovariant viruses, of immunosilent or occult carriage. NAT-based assays consist of three basic steps: extraction of nucleic acid, genome amplification mediated by procedures such as (RT)-PCR; strand-displacement amplification (SDA) and transcription-based amplification system TAS (Guatelli et al., Proc. Natl. Acad. Sci. 87: 1874-1878 (1990); Compton, Nature 350: 91-92 (1991)), and amplicon detection.
Currently available NAT assays are complex and entail multi-step procedures that require highly trained personnel and specialised facilities. They require cold-chain transport and storage of reagents, a high investment cost for instruments, high running costs for reagents, and regular maintenance support. All of these restrict the use of NAT only to specialized well-equipped and technically advanced laboratories. Correspondingly, current NAT assay design is unsuitable for near-patient and field-testing e.g. physician's office, community-based clinics, emergency rooms, battlefield surgery units or point-of care health centres, district hospitals and inner-city clinics in the resource-limited settings of developing countries. These include predominantly countries of Africa, Asia, and Latin America with a high prevalence of infectious diseases.
An essential requirement for assays based on nucleic acid amplification is protection from amplicon contamination, currently solved by working in specialized laboratories using dedicated spaces for sample preparation, amplification and detection. This approach is not applicable for field-testing, near-patient testing and in resource-limited settings.