278 Method Table 2 Influenza testing methods Test Time Specimen Sensitivity Specificity RITD Immuno-fluorescence 3 RT-PCR 4 Viral culture 5 Serologic tests 15 min. 1-4 h. 1-6 h. 1-10 d. 2 w. Respiratory samples 1 Respiratory samples 1 Respiratory samples 1 Respiratory samples 1 Serum 6 + ++ +++ ++ +++ +++ ++++ +++++ yes 2 yes yes yes no no yes yes RIDT rapid influenza diagnostic tests, RT-PCR reverse-transcriptase polymerase chain reaction (1) Appropriate respiratory samples vary for each method and should be obtained according to the manufacturer’s specifications (2) Some commercially-available RIDT distinguish between influenza A and B while others do not (3) Direct (DFA) or indirect (IFA) antibody staining (4) Conventional gel-based PCR, real-time RT-PCR, and multiplex PCR (5) Rapid viral cultures (shell vials) can yield results in 1-3 days, compared to conventional isolation in cell culture (3-10 days) Adapted from the IDSA and CDC guidelines [1 , 2 ] Curr Infect Dis Rep (2012) 14:275–283 Distinguishes influenza A from B Influenza A subtypes results to be available). During the 2009 H1N1 influenza A pandemic, it became clear that rapid case identification was essential for timely management of patients and for adequate public health actions to be taken. To answer to this threat, the CDC optimized the previously developed rRT-PCR proce- dures for detection of the A/H1N1 2009 pandemic influenza virus [36 ]. Yang et al. compared the performance of 12 rRT- PCR primer-probe sets designed for detecting the hemagglu- tinin (HA) or the neuraminidase (NA) gene of the pandemic influenza A/H1N1 2009 virus, using the primer-probe set developed at the CDC as reference. They found that although all primer-probe sets had specificity levels as high as 98.4 % to 100 %, some of the primer-probe sets had better specificity, sensitivity, and amplification efficiency than others, and that a combination of primer-probe sets targeted to the HA and genes had higher detection sensitivity than those targeting HA or individually [37]. In another study, Lam et al. showed that although rRT-PCR assays can be 10-fold more sensitive than cRT-PCR, newly developed cRT-PCR assays targeting the HA gene are a reliable alternative for laboratories where a rRT-PCR machine is not available [38]. Sensitivity and spec- ificity of these assays also depend on the type of respiratory sample employed. For example, in a Spanish study that assessed the utility of rRT-PCR for the diagnosis of the novel influenza A/H1N1 virus, the authors reported that the diag- nostic yield of combined nose and throat swabs was higher than that of nasopharyngeal aspirates [39]. Viral Cultures and Serologic Tests Even the fastest viral cultures techniques can take days to demonstrate influenza cytopathic effects. Since they are not suitable for initial clinical management, their utility during an influenza outbreak is to confirm some negative test results from RIDT and immunofluorescence. Viral cultures also pro- vide information about circulating influenza strains and its subtypes; this information is required for next season vaccine production, for surveillance of the emergence of new influen- za A strains, and for the detection of antiviral resistance. Similarly, serologic tests (i.e., hemagglutinin inhibition, ELISA, complement-fixation) that demonstrate a four-fold increase in serum antibody titers between acute and convales- cence phases of the disease, are only useful for retrospective diagnosis or research purposes (Table 2). Treatment and Prevention Annual immunization is the most important preventive mea- sure [40]. However, two classes of antiviral drugs are available and play an important role in the treatment and prevention of influenza [41 ]: the neuraminidase inhibitors (NI), oseltamivir and zanamivir, which are active against both influenza A and B viruses; and the M2 inhibitors, amantadine and rimantadine, which are active against all influenza A strains, but have no activity against influenza B viruses. In general, the duration for therapy with an NI is 5 days, and with the M2 inhibitors is three to 5 days. Pharmacology NI are sialic acid analogs that competitively inhibit neuramin- idase on the surface of both influenza A and B, thus interfering with the release of virus from infected cells. Oseltamivir phos- phate is an orally bioavailable prodrug that is rapidly absorbed from the gastrointestinal tract and is converted by hepatic esterases to the active metabolite, oseltamivir carboxylate. It has an elimination half-life of approximately 8 h, primarily