Role of laboratory in the virological diagnosis of pandemic Influenza A(H1N1)v

The new pandemic influenza, occurred in april 2009 in Mexico is also called swine Influenza. It is caused by a new Influenza virus A(H1N1)v, completely new, never before found in any species and results from complex genetic reassortment. The role of the laboratory is essential for the virological diagnosis of this emerging flu. It can provide the definitive diagnosis in patients whose clinical and epidemiological context is suggestive of infection with virus A(H1N1)v. The virological confirmation of an infection case caused by this virus is provided by the positivity of the laboratory following tests: RT-PCR and/or viral culture and/or four-fold rise in the rate of specific neutralizing antibodies directed against A(H1N1)v virus on a pair of sera collected two weeks apart. The real time RT-PCR is currently the tool of choice because of its rapidity, sensitivity and specificity. Immunological rapid diagnostic tests (RDTs) can detect the presence of the nucleoprotein antigens of seasonal influenza viruses type A and B. The evaluation of these tests showed, in the current pandemic context, a low sensitivity which not confer them a negative predictive value compatible with widespread use. Their results must be interpreted with caution and despite their good positive predictive value, they allow a presumptive diagnosis, confirmation by real time RT-PCR will be conducted whenever necessary.