Excess Mortality Associated with Influenza Epidemics in Portugal, 1980 to 2004

Abstract

BackgroundInfluenza epidemics have a substantial impact on human health, by increasing the mortality from pneumonia and influenza, respiratory and circulatory diseases, and all causes. This paper provides estimates of excess mortality rates associated with influenza virus circulation for 7 causes of death and 8 age groups in Portugal during the period of 1980–2004.Methodology/Principal FindingsWe compiled monthly mortality time series data by age for all-cause mortality, cerebrovascular diseases, ischemic heart diseases, diseases of the respiratory system, chronic respiratory diseases, pneumonia and influenza. We also used a control outcome, deaths from injuries. Age- and cause-specific baseline mortality was modelled by the ARIMA approach; excess deaths attributable to influenza were calculated by subtracting expected deaths from observed deaths during influenza epidemic periods. Influenza was associated with a seasonal average of 24.7 all-cause excess deaths per 100,000 inhabitants, approximately 90% of which were among seniors over 65 yrs. Excess mortality was 3–6 fold higher during seasons dominated by the A(H3N2) subtype than seasons dominated by A(H1N1)/B. High excess mortality impact was also seen in children under the age of four years. Seasonal excess mortality rates from all the studied causes of death were highly correlated with each other (Pearson correlation range, 0.65 to 0.95, P<0.001) and with seasonal rates of influenza-like-illness (ILI) among seniors over 65 years (Pearson correlation rho>0.64, P<0.05). By contrast, there was no correlation with excess mortality from injuries.Conclusions/SignificanceOur excess mortality approach is specific to influenza virus activity and produces influenza-related mortality rates for Portugal that are similar to those published for other countries. Our results indicate that all-cause excess mortality is a robust indicator of influenza burden in Portugal, and could be used to monitor the impact of influenza epidemics in this country. Additional studies are warranted to confirm these findings in other settings.

Influenza‐associated mortality in Yancheng, China, 2011‐15

“…We identified a greater impact of influenza A(H3N2) compared to influenza A(H1N1) and influenza B (Table 2, Table 3), which is similar to most other locations 3, 4, 6, 17, 19, 20. However, this observation is somewhat different to a previous study that estimated influenza B had a greater impact than influenza A(H3N2) in China, in the years 2003‐08 2.…”

Correlates of influenza vaccine uptake among community-dwelling older adults in Brazil

“…1,3,4 In particular, older adults are considered to be at a higher risk for influenza-associated excess of mortality. 5,6 Influenza vaccination is still the most effective way to prevent the disease and reduce the mortality rate among elderly individuals, albeit its efficacy in this age group is modest. 1 Antunes et al 7 observed a reduction of 26% in the overall mortality due to influenza and pneumonia after the introduction of annual mass vaccination.…”

Monitoreo de la actividad de influenza en Santa Fe, Argentina, 2005-2010

“…En los años 2006, 2008 y 2010 no se produjo un exceso de mortalidad, años en los que se observó la circulación de virus influenza B y subtipo de influenza A (H1N1), que se conoce tienen baja severidad evidenciada por varios autores 14,[32][33][34][35][36][37][38][39][40] . Esto podría deberse a que en el caso de cepas A (H1N1) han circulado desde 1918, con un intervalo entre 1957 y 1977, y se ha ido adaptando a la población humana y viceversa 38 .…”

“…Como consecuencia de la variabilidad de modelos aplicados a los datos de mortalidad utilizados en otros países, la comparación de los valores resulta muy compleja; sin embargo, se encuentran dentro del mismo rango 2,40 .…”

“…Los datos de mortalidad por neumonía e influenza han sido ampliamente utilizados 2,9-11,14,31 ; otros estudios han utilizado datos de mortalidad por todas las causas 32 o debido a causas cardíacas y respiratorias 40 ya que muchas muertes son causadas por complicaciones secundarias (fallas cardíacas) y al considerar la mortalidad solamente por neumonía e influenza como causa principal de muerte, estaríamos subestimando la carga de influenza. Por este motivo, en nuestro análisis se tuvo en cuenta la causa respiratoria en cualquier orden en el certificado de defunción.…”