Antiviral resistance is discussed in the next section.
Medscape Medical News. Collection of additional respiratory specimens for testing of influenza viruses by molecular assays should be considered for outpatients who are at high risk for influenza complications and hospitalized patients with suspected influenza, and antiviral treatment should be started promptly while molecular assay results are pending.Persons who receive live attenuated influenza virus vaccine for intranasal administration can shed influenza vaccine virus strains in the upper respiratory tract for up to 7 days after intranasal vaccination and can test positive during this period [123–125]. The target audience includes primary care clinicians, obstetricians, emergency medicine providers, hospitalists, and infectious disease specialists.The guidelines do not provide recommendations on infection prevention and control (IPC) measures for seasonal influenza in all healthcare settings; these are available on the Centers for Disease Control and Prevention (CDC) website [18]. In addition, oral oseltamivir had both significant virologic and clinical benefit compared with combination oseltamivir-zanamivir treatment, whereas the oseltamivir-zanamivir combination treatment had significant virologic, but not significant clinical, benefit compared with inhaled zanamivir [252].

These clinical practice guidelines are an update to the guidelines published by the IDSA in 2009, prior to the 2009 H1N1 influenza pandemic. One RCT of monotherapy with oral oseltamivir or inhaled zanamivir compared with combination oral oseltamivir plus inhaled zanamivir treatment or placebo in adult outpatients with laboratory-confirmed influenza reported that oral oseltamivir demonstrated both significant reduction in viral shedding at day 2 of treatment and significant reduction in the median time to resolution of illness symptoms compared with inhaled zanamivir [252]. One RCT of oseltamivir chemoprophylaxis for 10 days vs placebo in frail elderly patients in long-term care facility units after a single laboratory-confirmed case of influenza over 4 seasons in the Netherlands did not find a significant benefit; however, this study was underpowered due to fewer influenza outbreaks than expected [440]. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations.

Image courtesy of the World Health Organization.Colorized transmission electron micrograph shows avian influenza A H5N1 viruses (gold) grown in MDCK cells (green). News,encoded search term (Influenza) and Influenza,Trending Clinical Topic: Flu Vaccine Recommendations.Fast Five Quiz: Do You Know Current Vaccination Recommendations?Trending Clinical Topics for January 2019,H1N1 Influenza A (Swine Flu) Alert Center,CDC's Messonnier Says She Trusts COVID Vaccine Process,Potential New Swine Flu Pandemic Stirring in China,Dear Commissioner Hahn: Tell the Truth or Resign.What Is the Risk of Catching the Coronavirus on a Plane?Restaurants May Be Key Component to COVID-19 Spread,Hydroxychloroquine RCTs: 'Ethically, the Choice Is Clear',Wear a Mask While Having Sex, Canada's Top Doctor Suggests,Up to 7.3 Million Americans Sickened by Flu So Far, CDC Says.Share cases and questions with Physicians on Medscape consult.Viral Culture and Polymerase Chain Reaction Testing,Direct Immunofluorescent Tests and Serologic Testing,American Academy of Pediatrics Guidelines on Influenza Vaccination in Children,Infectious Disease Society of America (IDSA) Guidelines for Influenza Testing and Antiviral Therapy,https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm,http://www.medscape.com/viewarticle/776271?src=nl_newsalert,http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm294057.htm,http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/ucm108892.htm,https://www.cdc.gov/flu/protect/vaccine/egg-allergies.htm,http://www.cdc.gov/flu/professionals/diagnosis/molecular-assays.htm,http://www.who.int/mediacentre/factsheets/avian_influenza/en/print.html,http://www.who.int/influenza/human_animal_interface/EN_GIP_20120810CumulativeNumberH5N1cases.pdf,https://www.medscape.com/viewarticle/923428,http://www.who.int/mediacentre/factsheets/fs211/en,http://www.cdc.gov/flu/about/season/current-season.htm,http://www.cdc.gov/flu/avianflu/avian-in-humans.htm,http://link.springer.com/article/10.1007/s00125-013-3158-8#,http://www.medscape.com/viewarticle/819737,http://www.cdc.gov/flu/avianflu/guidance-labtesting.htm,http://www.who.int/influenza/resources/documents/ClinicalManagement07.pdf,http://www.who.int/csr/disease/avian_influenza/Timeline_2007_03_20.pdf,http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/TipsandArticlesonDeviceSafety/ucm109432.htm%20,http://www.medscape.com/viewarticle/826847,http://news.alere.com/~/media/Files/A/Alere-Newsroom/press-release/Alere_i_US_release_6_16_2014.pdf,http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm149557.htm,http://www.medscape.com/viewarticle/805620,https://www.cdc.gov/vaccines/schedules/hcp/adult.html,https://www.medscape.com/viewarticle/911374,http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm328982.htm,https://abcnews.go.com/Health/wireStory/flu-vaccine-works-traditional-shot-56033657,http://www.medscape.com/viewarticle/777773,http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm335891.htm,http://www.fda.gov/BiologicsBloodVaccines/Vaccines/QuestionsaboutVaccines/ucm080753.htm,http://www.who.int/influenza/vaccines/virus/h5n1virus09march/en/index.html,http://www.cdc.gov/flu/protect/habits.htm,https://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm,http://www.cdc.gov/flu/professionals/antivirals/index.htm,http://www.medscape.com/viewarticle/885567,https://www.medscape.com/viewarticle/892970,http://www.medscape.com/viewarticle/885217,http://www.cdc.gov/media/releases/2016/s0622-laiv-flu.html,https://www.cbsnews.com/news/how-effective-is-this-years-flu-shot/,https://www.cdc.gov/flu/weekly/summary.htm,https://www.medscape.com/viewarticle/891870,https://www.medscape.com/viewarticle/891265,American Association for the Advancement of Science,Southern Society for Clinical Investigation,Alliance for the Prudent Use of Antibiotics,American Association of University Professors,American Clinical and Climatological Association,Association for Professionals in Infection Control and Epidemiology,Infectious Disease Society for Obstetrics and Gynecology,Southwestern Association of Clinical Microbiology.

They have higher sensitivity than RIDTs, but lower sensitivity and specificity compared with viral isolation in cell culture or RT-PCR. The development of oseltamivir resistance during chemoprophylaxis has been reported, usually with the H275Y mutation, with limited ongoing transmission of resistant virus [96, 336, 358, 406]. While data are limited on the optimal duration of antiviral chemoprophylaxis to control institutional influenza outbreaks, the CDC recommends that antiviral chemoprophylaxis should be administered initially for 14 days, and if surveillance indicates that new cases continue to occur, chemoprophylaxis should be continued until 7 days after the last case has been identified [458].Following global consultations with multiple stakeholders, the WHO posted a comprehensive influenza research agenda in 2009 that addressed research gaps including surveillance, the animal–human interface, novel influenza A virus infections, transmission, vaccines and other prevention strategies, diagnostics, disease pathogenesis, antivirals, and clinical management. In patients with influenza B, baloxavir significantly reduced the median time to improvement of symptoms by 26 hours compared with placebo (P < .0138) and 27 hours compared with oseltamivir (P < .0251) [460]. Based upon available evidence, recommendations are provided below for specific antiviral agents, route, dosing, and duration of therapy.Oseltamivir treatment is associated with gastrointestinal symptoms.

Higher sensitivity to detect influenza viruses in respiratory specimens has been reported for one rapid molecular assay (isothermal nucleic acid amplification) than for rapid antigen detection tests [117–119], and a meta-analysis of rapid molecular assays reported pooled sensitivities of 92% and 95% for detection of influenza A and B viruses, respectively, and pooled specificities of 99% [111].The timing and site of respiratory specimen collection can affect influenza testing results. Nasal Flu Vaccine Back on CDC List of Recommended Vaccines.Brown T. AAP Recommends Flu Vaccine for All Kids Older Than 6 Months. In this study, 40% of high-risk persons presented for medical care within 2 days of illness onset. Seasonal Influenza (Flu): Antiviral Drugs. You must declare any conflicts of interest related to your comments and responses.

Background information about signs and symptoms of influenza, complications, groups considered to be at high risk of complications, and influenza tests are included in the next section.

“High influenza activity” is defined as increased circulation of seasonal influenza A and B viruses, such as peak weeks of circulation of seasonal influenza A and B viruses during the colder fall, winter, and spring months in the United States.