TY - JOUR
TI - Association between type -specific influenza circulation and incidence
of severe laboratory -confirmed cases; which subtype is the most
virulent?
AU - Lytras, T.
AU - Andreopoulou, A.
AU - Gkolfinopoulou, K.
AU - Mouratidou,
AU - E.
AU - Tsiodras, S.
JO - Clinical Microbiology and Infection
PY - 2020
VL - 26
TODO - 7
SP - 922-927
PB - Elsevier Sci Ltd, Exeter, United Kingdom
SN - 1198-743X
TODO - 10.1016/j.cmi.2019.11.018
TODO - Epidemiology; Influenza; Influenza complications; Intensive care units;
Mortality
TODO - Objectives: Excess population mortality during winter is most often
associated with influenza A(H3N2), though susceptibility differs by age.
We examined differences between influenza types/subtypes in their
association with severe laboratory -confirmed cases, overall and by age
group, to determine which type is the most virulent. Methods: We used
nine seasons of comprehensive nationwide surveillance data from Greece
(2010 - 2011 to 2018-2019) to examine the association, separately for
influenza A(H1N1)pdm09, A(H3N2) and B, between the number of laboratory
-confirmed severe cases (intensive care hospitalizations or deaths) per
type/subtype and the overall type -specific circulation during the
season (expressed as a cumulative incidence proxy). Quasi -Poisson
models with identity link were used, and multiple imputation to handle
missing influenza A subtype. Results: For the same level of viral
circulation and across all ages, influenza A(H1N1)pdm09 was asso- ciated
with twice as many intensive care hospitalizations as A(H3N2) (rate
ratio (RR) 1.89, 95% CI 1.38 - 2.74) and three times more than
influenza B (RR 3.27, 95%CI 2.54-4.20). Similar associations were
observed for laboratory -confirmed deaths. A(H1N1)pdm09 affected adults
over 40 years at similar rates, whereas A(H3N2) affected elderly people
at a much higher rate than younger persons ( 65 vs. 40 - 64 years, RR
for intensive care 5.42, 95% CI 3.45-8.65, and RR for death 6.19,
95%CI 4.05-9.38). Within the 40-64 years age group, A(H1N1)pdm09 was
associated with an approximately five times higher rate of severe
disease than both A(H3N2) and B. Discussion: Influenza A(H1N1)pdm09 is
associated with many more severe laboratory -confirmed cases, likely due
to a more typical clinical presentation and younger patient age, leading
to more testing. A(H3N2) affects older people more, with cases less
often recognized and confirmed. T. Lytras, Clin Microbiol Infect
2020;26:922
ER -