The role of laboratory diagnosis of influenza

ABSTRACT

INTRODUCTIONSince 1948 the World Health Organization (WHO) has established an international network of laboratories for the surveillance of influenza viruses. Currently, the Global Influenza Surveillance Network (GISN) includes 128 National Influenza Centers (NICs) distributed in 89 countries. Among their attributions the NICs are responsible for collecting and receiving specimens and virus isolates from patients suspected of being infected with influenza viruses and conducting preliminary laboratory analysis. Representative virus isolates are then selected and shipped to one of four specialized WHO Collaborating Centers (WHOCCs) for reference purposes and for advanced antigenic and genetic influenza analysis. Based on the results of this, the WHO makes an annual recommendation on influenza vaccine composition. NICs also alert the WHO to unusual outbreaks of influenza or influenza-like illness, and they detect non-subtypable and low-reacting virus isolates using the WHO diagnostic reagents provided through the GISN. Under the agreed terms of reference (www.who.int/csr/disease/influenza/TORNICs.pdf), NICs must disseminate the generated data in FluNet (www.who.int/flunet), a webbased tool for the support and coordination of national and global influenza surveillance and reporting. Laboratory diagnosis of influenza is an important public health tool that has become a cornerstone of the prevention, containment, surveillance and therapeutic management of patients. In this context, there are a variety of laboratory methods that allow the identification of influenza viruses circulating in the community. Diagnostic approaches for the identification of the virus include viral culture, detection of viral antigens (e.g., immunofluorescence tests), and nucleic acid testing methods. A presumptive diagnosis can be made by a validated rapid antigen test. Antibody detection is usually accomplished by virus neutralization (NT) and hemagglutination inhibition (HI) tests, which