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- Influenza A (seasonal):
- 2017-2018, judged a highly severe season, H3N2 (influenza A) was the predominant isolate. Nationally, influenza A was 71.2%, influenza B 28.8%. Subtyping of isolates identified influenza A(H3N2) 84.9%, influenza A(H1N1)pdm09 15.1%.
- 2018-2019, season longest in a decade > 20 weeks with two waves of influenza A (H1N1 pdm09 predominated early with H3N2 seen more in Feb-May).
- Influenza A: recently active strains
- H1n1 pdm09 active annually since 2009; in 2018-2019 accounted for most of the early season.
- H3N2: seasonal influenza, predominant strain in 2017-2018 and late 2018-2019 in the U.S.
- H1N1v: detected Jan 2015 with a handful of reported infections in the U.S.
- Other novel strains (usually limited): A(H1N2) variant (H1N2v) virus (2016), A(H7N2) (2016)
- H3N2v: Swine influenza strain with triple re-assortment, emerging 2011-2013 in multiple states in the U.S., continues to circulate including in 2017.
- Most human cases have had pig contact.
- Strain has been susceptible to neuraminidases.
- People at high risk for severe consequences with influenza should avoid pig contact.
- Children < 10 yrs may be most prone as older children and adults may have some immunity by exposure to earlier influenza strains.
- No clear indication of increased severity of disease.
- Pandemic H1N1, remains active since pandemic 2009, continues to be identified in seasonal influenza.
- Other: multiple avian influenza or other strains
- Influenza B (seasonal): typically becomes more common later in a seasonal influenza season.