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Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) assessed antiviral susceptibility of 14,330 influenza A and B viruses collected by WHO-recognized National Influenza Centres (NICs) between May 2015 and May 2016. Neuraminidase (NA) inhibition assay was used to determine 50% inhibitory concentration (IC 50 ) data for NA inhibitors (NAIs) oseltamivir, zanamivir, peramivir and laninamivir. Furthermore, NA sequences from 13,484 influenza viruses were retrieved from public sequence databases and screened for amino acid substitutions (AAS) associated with reduced inhibition (RI) or highly reduced inhibition (HRI) by NAIs. Of the viruses tested by WHO CCs 93% were from three WHO regions: Western Pacific, the Americas and Europe. Approximately 0.8% (n = 113) exhibited either RI or HRI by at least one of four NAIs. As in previous seasons, the most common NA AAS was H275Y in A(H1N1)pdm09 viruses, which confers HRI by oseltamivir and peramivir. Two A(H1N1)pdm09 viruses carried a rare NA AAS, S247R, shown in this study to confer RI/HRI by the four NAIs. The overall frequency of A(H1N1)pdm09 viruses containing NA AAS associated with RI/HRI was approximately 1.8% (125/6915), which is slightly higher than in the previous 2014-15 season (0.5%). Three B/Victoria-lineage viruses contained a new AAS, NA H134N, which conferred HRI by zanamivir and laninamivir, and borderline HRI by peramivir. A single B/Victoria-lineage virus harboured NA G104E, which was associated with HRI by all four NAIs. The overall frequency of RI/HRI phenotype among type B viruses was approximately 0.6% (43/7677), which is lower than that in the previous season. Overall, the vast majority (>99%) of the viruses tested by WHO CCs were susceptible to all four NAIs, showing normal inhibition (NI). Hence, NAIs remain the recommended antivirals for treatment of influenza virus infections. Nevertheless, our data indicate that it is prudent to continue drug susceptibility monitoring using both NAI assay and sequence analysis. [ABSTRACT FROM AUTHOR]

Introduction. Understanding the seasonality of influenza can help inform prevention and clinical treatment strategies. The aim of this manuscript is to describe the trends and epidemiology of outpatient influenza in South Africa prior to the influenza A(H1N1) pandemic.Methods. Throughout each year, participating healthcare practitioners sent throat swabs from patients with influenza-like illness (ILI) to the National Institute for Communicable Diseases for influenza testing by immunofluorescence and viral culture through the Viral Watch influenza surveillance program.Results. From 1984 to 2004, participating sites were restricted to 1 province and the annual number of specimens ranged from 91 to 534. In 2005 the program was expanded. By 2008 the program included all 9 provinces; 1276 specimens were submitted that year. The mean week of onset was the first week of June and the mean peak was the first week of July. The duration of the season ranged from 6 to 18 weeks with a mean of 10 weeks. The mean annual influenza detection rate was 28% (range, 23%–41%). Influenza A(H3N2) predominated in 14 (56%) of the 25 years, seasonal influenza A(H1N1) in 7 (28%), and influenza B in 2 (8%), and in 2 years multiple types cocirculated.Conclusions. The program has provided valuable data on the timing of the influenza season each year that can be useful to direct the timing of vaccination and assist clinicians in deciding whether to prescribe empirical antiviral therapy. [ABSTRACT FROM AUTHOR]

The formulation of accurate clinical case definitions is an integral part of an effective process of public health surveillance. Although such definitions should, ideally, be based on a standardized and fixed collection of defining criteria, they often require revision to reflect new knowledge of the condition involved and improvements in diagnostic testing. Optimal case definitions also need to have a balance of sensitivity and specificity that reflects their intended use. After the 2009-2010 H1N1 influenza pandemic, the World Health Organization (WHO) initiated a technical consultation on global influenza surveillance. This prompted improvements in the sensitivity and specificity of the case definition for influenza - i.e. a respiratory disease that lacks uniquely defining symptomology. The revision process not only modified the definition of influenza-like illness, to include a simplified list of the criteria shown to be most predictive of influenza infection, but also clarified the language used for the definition, to enhance interpretability. To capture severe cases of influenza that required hospitalization, a new case definition was also developed for severe acute respiratory infection in all age groups. The new definitions have been found to capture more cases without compromising specificity. Despite the challenge still posed in the clinical separation of influenza from other respiratory infections, the global use of the new WHO case definitions should help determine global trends in the characteristics and transmission of influenza viruses and the associated disease burden. [ABSTRACT FROM AUTHOR]