Blood-Borne Disease

The use of nucleic acid tests (NAT) has dramatically enhanced the detection and management of blood-borne viruses. Some of the very first applications of NAT using polymerase chain reaction (PCR) were in the identification of HIV in blood. The recognition of other blood-borne viruses, in particular hepatitis B and hepatitis C, further prompted the application of molecular tests to clinical medicine. It was the ease of transmission of viruses through blood and blood products that was one of the main stimuli for the development of nucleic acid testing (NAT) in virology. The improvements in technology leading to automation, reduction in contamination, quantitation and increased sensitivity have enhanced this development and are likely to continue and expand, and so further improve patient management – hopefully with reductions in cost. The introduction of these more sensitive NAT assays has further reduced the likelihood of the acquisition of blood-borne viruses during transfusion or transplantation. The development of commercial viral load assays, or quantitative NAT, has revolutionised for example the clinical management of HIV infection and of other systemic diseases (e.g. cytomegalovirus, Epstein-Barr virus, HHV-6, BK polyomavirus) that are a particular clinical issue in immunocompromised individuals (Table 6.1). Also, resistance genotyping tests can now be performed by sequencing the relevant drug targets e.g. HIV – most commonly the reverse transcriptase and protease regions, but now including integrase and envelope gp 41. Infections in immunocompromised patients may occur in the absence of classical symptoms and the use of PCR to diagnose, in a targeted fashion, the most common infections has revolutionised treatment of these infections in the immunocompromised patient. Knowledge of the most likely agents – for example, CMV in the first 3 months following bone marrow transplant, is often used because such reactivation infection is extremely common (and often fatal) in this population. The availability of polyoma virus PCR means a clinical transplant service is able to monitor their patients for polyoma virus and adjust the level of immunosuppression appropriately. The availability of rapid diagnosis for fungi or Pneumocystis means transplant clinical services can often reduce the use of antimicrobial prophylaxis for these agents. Therefore, as a result of these rapid diagnostic nucleic acid testing services, clinical services can directly improve patient therapy, thereby reducing side effects and improving outcomes as well as saving money.