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Abstract
Influenza and respiratory syncytial virus (RSV) cause substantial morbidity and mortality.
Statistical methods used to estimate deaths in the United States attributable to influenza
have not accounted for RSV circulation.
To develop a statistical model using national mortality and viral surveillance data
to estimate annual influenza- and RSV-associated deaths in the United States, by age
group, virus, and influenza type and subtype.
Age-specific Poisson regression models using national viral surveillance data for
the 1976-1977 through 1998-1999 seasons were used to estimate influenza-associated
deaths. Influenza- and RSV-associated deaths were simultaneously estimated for the
1990-1991 through 1998-1999 seasons.
Attributable deaths for 3 categories: underlying pneumonia and influenza, underlying
respiratory and circulatory, and all causes.
Annual estimates of influenza-associated deaths increased significantly between the
1976-1977 and 1998-1999 seasons for all 3 death categories (P<.001 for each category).
For the 1990-1991 through 1998-1999 seasons, the greatest mean numbers of deaths were
associated with influenza A(H3N2) viruses, followed by RSV, influenza B, and influenza
A(H1N1). Influenza viruses and RSV, respectively, were associated with annual means
(SD) of 8097 (3084) and 2707 (196) underlying pneumonia and influenza deaths, 36 155
(11 055) and 11 321 (668) underlying respiratory and circulatory deaths, and 51 203
(15 081) and 17 358 (1086) all-cause deaths. For underlying respiratory and circulatory
deaths, 90% of influenza- and 78% of RSV-associated deaths occurred among persons
aged 65 years or older. Influenza was associated with more deaths than RSV in all
age groups except for children younger than 1 year. On average, influenza was associated
with 3 times as many deaths as RSV.
Mortality associated with both influenza and RSV circulation disproportionately affects
elderly persons. Influenza deaths have increased substantially in the last 2 decades,
in part because of aging of the population, underscoring the need for better prevention
measures, including more effective vaccines and vaccination programs for elderly persons.