Rapid testing vital in tackling Bird Flu
SummaryDr Adam Meijer of the Netherlands-based European Influenza Surveillance Scheme (EISS)§ has highlighted the vital role rapid testing must play in combating the global threat of bird flu. Dr Meijer makes his observations in the January issue of Expert Review of Molecular Diagnostics.
Dr Adam Meijer of the Netherlands-based European Influenza Surveillance Scheme (EISS)§ has highlighted the vital role rapid testing must play in combating the global threat of bird flu. Dr Meijer makes his observations in the January issue of Expert Review of Molecular Diagnostics.
Until now, the last requirement for avian influenza viruses to cause a pandemic –
efficient transmission between humans – has fortunately not been met. However, the devastating effect of the A(H5N1) bird flu on poultry holdings, and hence on economics and food supply, and the threat of the influenza A(H5N1) virus possibly becoming the next pandemic virus are eminent.
Meijer points out that the current window of opportunity to intervene is measured in days, so that rapid, simple and low-cost tests for diagnosis could be of great help in combating the global threat of bird flu. The very first step to combat an infectious disease is the early detection of infection, and before that the recognition of a suspect case. Recognition of bird flu in humans is quite difficult as the initial symptoms are not very specific.
Rapid diagnosis is needed to commence measures to limit further spread of avian and human bird flu and to start therapy in case of human bird flu. Human therapy with oseltamivir (Tamiflu®) decreases the severity of the symptoms and reduces shedding of virus, thus limiting spread and possible generation of viruses capable to transmit effectively between people. However, therapy is only effective when administered within 48 hours after onset of symptoms. In addition, modeling has shown that in the absence of an effective human vaccine, and under certain conditions, an emerging pandemic could effectively be snuffed out using antiviral agents if geographically targeted prophylaxis starts as quickly as possible. This again underlines the need for strengthened surveillance using rapid diagnostic tests.
There are basically three rapid test categories for diagnosis of bird flu:
i) near patient tests (NPT) and field antigen detection tests
ii) laboratory antigen detection tests and
iii) tests using nucleic acid amplification techniques (NAT).
NPTs are commercially available for the diagnosis of human influenza and provide results within approximately 30 minutes. The European Influenza Surveillance Scheme (EISS) task group on near patient test recommended use of NPT data as an adjunct to virus isolation for early warning of a change in influenza activity in humans. Adjunct, because the sensitivity is limited to 70-75% compared to virus isolation and NAT. Because of this and other sensitivity issues, Meijer does not recommend these NPTs for bird flu diagnosis, until they are thoroughly validated for this purpose.
Antigen detection tests must be carried out in the laboratory, and although this type of test can provide results within hours, their sensitivity is less than virus isolation, the gold standard, and therefore only recommended when the superior NAT type test is not available.
The NAT test type is most sensitive as compared to virus isolation; these add 2-13% to the detection rate and in real-time format results can be obtained within 4 hours. A disadvantage of this type of test is the complexity of the test and the requirement of expensive equipment which are barriers to use NAT, especially for laboratories in poorer nations. Commercial kits for specific detection of the H5 gene are already available from at least four companies: HKDNA Ltd, Hong Kong SAR, China; EuroClone SpA, Milan, Italy; AJ Roboscreen, Leipzig, Germany; and Qiagen NV, Venlo, The Netherlands.
Meijer recommends using, wherever possible, NAT as rapid test for bird flu diagnosis, but only by well trained laboratories. Confirmation by an internationally recognized reference laboratory for human A(H5) infection (WHO) or avian influenza (OIE) is required, but this should not delay taking measures.
Meijer stresses, however, that rapid tests should never replace virus isolation fully as the virus itself is still needed to study the characteristics and evolution of the virus and for selection of vaccine candidates.
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1. Importance of rapid testing to combat the global threat of bird flu by Adam Meijer. Expert Review of Molecular Diagnostics (2006) 6(1) pp. 1-4
ABOUT THE EISS
§The European Influenza Surveillance Scheme (EISS) was established in 1996. EISS is a recognized European Designated Surveillance Network and is funded by the European Commission (EC). The main activity of EISS is the collection and analysis of epidemiological and virological influenza surveillance data from the 25 European Union (EU) Member States and Norway, Romania and Switzerland. Roughly 13,000 sentinel physicians covering a total population of 464 million inhabitants report clinical morbidity data and 38 national reference laboratories report virological data. The co-ordination of the scheme is based at the Netherlands Institute for Health Services Research (www.nivel.nl), Utrecht, The Netherlands. The laboratories are organized in the Community Network of Reference Laboratories for Human Influenza in Europe, which is managed from the EISS Co-ordination Centre (EISS-CC) in close collaboration with the World Health Organization (WHO). During the influenza season the EISS-CC team publishes a Weekly Electronic Bulletin on the EISS website (www.eiss.org). The EISS members, who are leading national influenza epidemiologists and virologists, and the EISS-CC team, contribute also to pandemic preparedness through their active participation in EC, European Centre for Disease Prevention and Control (ECDC) and WHO activities related to this subject.
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