AMMI Canada issues 2023 update on influenza—management and emerging issues

The Association of Medical Microbiology and Infectious Disease Canada (AMMI Canada) has issued an update to the existing AMMI Canada guidance on seasonal influenza. The update provides an overview of five main issues: Characteristics of the 2022–2023 influenza season. Prevention of influenza. Influenza antiviral use to reduce the impact of influenza on the healthcare system. The potential role of multiplex respiratory testing, which includes the detection of SARS-CoV-2, influenza virus and respiratory syncytial virus (RSV) in a single test. Emerging issues related to highly pathogenic avian influenza (HPAI) virus.1 1. Characteristics of the 2022–2023 influenza season The 2022–2023 fall/winter season saw an unprecedented very early rise in seasonal influenza cases compared to the preceding two years. The low number of cases in the previous two years was most likely due to public health measures implemented during the COVID-19 pandemic. Influenza-associated hospitalizations increased dramatically during the 2022–2023 influenza season, particularly among young children, a population that also experienced high levels of severe RSV disease.1 Although the impact of seasonal influenza was seen primarily in children this past season, it also affected older age groups. Ensuring prevention measures (e.g., immunization) are used, along with timely access to influenza treatment with neuraminidase inhibitors (e.g., oseltamivir) when indicated, can reduce illness and healthcare system strain.1 2. Prevention of influenza Influenza vaccination is recommended for all Canadians six months of age or older. It is particularly important for certain groups because risks are higher in some settings and for some individuals. Influenza and COVID-19 vaccines can be co-administered at the same visit, when applicable, to facilitate recommended immunizations.1 Although the quality of data varies, hand hygiene and wearing masks when in poorly ventilated crowded places are safe and reasonable options for individuals to reduce their risk during the respiratory virus season.1 3. Antiviral post-exposure chemoprophylaxis AMMI Canada published guidance on the use of chemoprophylaxis with neuraminidase inhibitors (oseltamivir, zanamivir) to protect individuals against influenza after exposure, in 2013,2 with an update in 2019.3 The recommendations in these documents remain appropriate. However, some questions remain, including the efficacy and optimal duration of chemoprophylaxis when used in facility-based outbreak settings.1 Recent analyses and expert opinion support the potential effectiveness of chemoprophylaxis post-exposure, but focused, limited and timely short-term use is advised. Durations shorter than 10 days of oseltamivir chemoprophylaxis may be adequate. With seasonal influenza, early therapy is preferred over post-exposure prophylaxis in community settings.1 Use of chemoprophylaxis should be balanced against the risk for the emergence of antiviral resistance when prophylactic neuraminidase inhibitors are used for prolonged periods or when chemoprophylaxis is started late post-exposure relative to the short incubation period of influenza viruses (typically 1–4 days [mean 2 days] for seasonal influenza).1 The AMMI Canada update includes an algorithm for oseltamivir and zanamivir use for prophylaxis or early treatment in close contacts of a suspected or laboratory-confirmed case. The algorithm now also incorporates chemoprophylaxis recommendations for highly pathogenic avian influenza exposures.1 Ambulatory antiviral therapy to reduce influenza burden on the healthcare system The indications and dosing for seasonal influenza antiviral agents have not changed from the 2013 and 2019 AMMI Canada documents. When influenza is circulating in the community, the decision to initiate therapy with influenza antivirals for outpatients with possible influenza should be based on their risk factors, and the severity of their clinical presentation (e.g., pneumonia) or exacerbation of underlying chronic medical condition. Antiviral therapy should be prescribed as soon as possible when indicated.1 Ambulatory antiviral treatment, when indicated, has the potential to help to ease the burden on the healthcare system. Early treatment with oseltamivir has been shown to lead to shorter duration of symptoms and fewer complications requiring antibiotics in adults and children. It may also reduce the risk of hospitalization, particularly when prescribed earlier in the course of infection. As the effectiveness of oseltamivir is optimized when administered early in laboratory-confirmed infection, consideration should be given to increasing access to both influenza testing and timely oseltamivir treatment for individuals at higher risk.1 4. Potential role of multiplex respiratory testing Influenza virus, SARS-CoV-2 and RSV infections cannot be reliably differentiated based on clinical presentation since they cause a range of overlapping respiratory and systemic symptoms. This makes management challenging when all three viruses are circulating. Many commercial assays have moved away from detection of SARS-CoV-2 alone to multiplex nucleic acid amplification testing (NAAT) that can identify any of these viruses in a single reaction.1 Currently, influenza testing is not routinely recommended for ambulatory patients in many jurisdictions, in part due to cost considerations. However, given the overlapping risk factors for complications and severe disease, many patients being tested for COVID-19 treatment would also potentially benefit from antiviral treatment for influenza if it was identified.1 The use of multiplex testing among the highest risk individuals would facilitate early use of antivirals for influenza and/or COVID-19. For this approach to be optimized, easy and equitable access to testing and treatment would need to be addressed.1 5. Emerging issues related to highly pathogenic avian influenza (HPAI) virus The AMMI Canada update discusses avian cases of HPAI virus in Canada. Confirmed human infection and illness with HPAI viruses is uncommon and typically associated with direct exposure to birds or environments known to be contaminated with the virus. However, H5N1 viral spillover to mammalian species has already been detected in a substantial number of free-ranging terrestrial and marine mammals in Japan, Europe and the Americas, raising substantial concern for future human and animal health.1 HPAI viral infections in humans range from asymptomatic to severe influenza-like illness, may include conjunctivitis or meningoencephalitis, and may result in death. Timely diagnosis and reporting are key factors for successful outcomes with use of antiviral therapy or chemoprophylaxis.1 Antiviral recommendations for avian influenza are outlined in the document, as well as key considerations when prescribing antivirals for HPAI prevention or treatment.1 References 1. 1. Harrison R, Mubareka S, Papenburg J, et al. AMMI Canada 2023 update on influenza: management and emerging issues. J Assoc Med Microbiol Infect Dis Can 2023;8(3):176-86.(accessed November 9, 2023). 2. Aoki FY, Allen UD, Stiver HG, et al. The use of antiviral drugs for influenza: a foundation document for practitioners. Can Infect Dis Med Microbiol 2013;24(Suppl C):1C-15C. 3. Aoki FY, Allen UD, Mubareka S, et al. Use of antiviral drugs for seasonal influenza: foundation document for practitioners—Update 2019. J Assoc Med Microbiol Infect Dis Can 2019;4(2):60-82.(accessed November 9, 2023).

AMMI Canada issues 2023 update on influenza—management and emerging issues

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