influenza-associated mortality has traditionally been estimated as the
excess mortality above a baseline of deaths during influenza epidemic
periods. Excess mortality estimates are not timely, because national
vital statistics data became available after a period of 2-3 years. To
develop a method for timely reporting, we used the 121 Cities Surveil
lance System (121 Cities), maintained at the Centers for Disease Contr
ol and Prevention, as an alternative data source. We fit a cyclical re
gression model to time series of weekly 121 Cities pneumonia and influ
enza deaths for 1972-1996 to estimate the excess pneumonia and influen
za mortality and to compare these figures with national vital statisti
cs estimates for 20 influenza seasons during 1972-1992. Seasonal exces
s mortality based on 121 Cities correlated well with the national data
: for 18 (90%) of 20 seasons, our influenza epidemic severity index ca
tegory approximated the result based on national vital statistics. We
generated preliminary severity categories for the four recent seasons
during 1992-1996. We conclude that the 121 Cities Surveillance System
can be used for the timely assessment of the severity of future influe
nza epidemics and pandemics, Timely pneumonia and influenza mortality
reporting systems established in sentinel countries worldwide would he
lp alert public health officials and allow prompt prevention and inter
vention strategies during future influenza epidemics and pandemics.