121 Cities Mortality Reporting System

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History

Overview

As part of its national influenza surveillance effort, the Centers for Disease Control and Prevention (CDC) receives weekly mortality reports from 122* cities and metropolitan areas in the United States within 2-3 weeks from the date of death. These reports summarize the total number of deaths occurring in these cities/areas each week, as well as the number due to pneumonia and influenza. This system consistently covers approximately one-third of the deaths in the United States and provides CDC epidemiologists with preliminary information with which to evaluate the impact of influenza on mortality in the United States and the severity of the currently circulating virus strains. The advantage of this system is that it provides timely data 2 to 3 years before finalized mortality data are available from the National Center for Health Statistics (NCHS). The system does not provide incidence rates, as deaths are reported to CDC by place of occurrence, and not by place of residence.

Historical Development

In the late 1800's and early 1900's pneumonia and influenza deaths were reported to state and federal health officials only in times of an epidemic. Health officials would then conduct personal interviews to collect information about the age, sex, severity of illness, and other demographic information regarding cases in the household. The results of these interviews were the only source of mortality information available to researchers for measurement of the impact of an epidemic or prediction of future trends (Collins, et al. 1951).

In response to the influenza pandemic of 1918-1919, the U.S. Bureau of the Census reported one of the first quantitative measurements of the epidemic impact on mortality. In the March 4, 1919, issue of the "Weekly Health Index," the death rates for 31 large cities for the period of September 18, 1918-March 1, 1919 were compared to the death rates for the same period in 1917-1918, and the difference between them was calculated as the "excess mortality" during the epidemic.

Selwyn Collins further refined this concept of a quantitative measure or index of the impact of influenza epidemics in the 1930's. He used his refined method to characterize influenza epidemics for data collected monthly from 35 cities (1910-1919) and weekly from 90 cities (1920-1942), 56 cities (1943-1950), and 62 cities (1951-1956).

In 1957, fear of the Asian flu prompted the CDC (formerly Communicable Disease Center) to develop a method of early detection of an epidemic using a modification of Collins' procedures. At this time, the system consisted of 108 cities from which Collins had previously been collecting weekly (unpublished) data (Serfling, et al. 1962).

In 1962, after responsibility for publication of the Morbidity and Mortality Weekly Report (MMWR) was transferred to CDC from the National Office of Vital Statistics, CDC continued to collect weekly mortality data reported voluntarily by a number of selected cities in the United States.

In 1970, CDC's weekly mortality reporting network consisted of 123 cities. This became 121 cities when Flint, Michigan, and Oklahoma City, Oklahoma, dropped out of the system in 1972. Two additional changes in the cities reporting occurred on November 10, 1991, when Oakland, California was replaced by Santa Cruz, California; and on July 12, 1992 when Louisville, Kentucky was replaced by Lexington, Kentucky. These changes were necessitated by budget restrictions in California and changes in state registration procedures in Kentucky. The latest change to the 121 Cities Mortality Reporting System came on January 1, 1997. Madison (Dane County), Wisconsin, is no longer participating in the system and because of its large catchment area, it was replaced by two county reporting areas: Boise (Ada County), Idaho, and Lansing (Ingham County), Michigan. The current participating 122 cities and metropolitan areas are located in 33 states plus the District of Columbia and are listed by Census Region in Table IV of the MMWR.

Today, the 121 Cities Mortality Reporting System continues to serve as the most timely source of mortality data in the United States. Despite changes in the methods for reporting and the cities participating, the system has consistently captured one-third of the nation's deaths. Furthermore, evaluations have shown that the 121 Cities Mortality Reporting System detects trends and patterns in pneumonia and influenza deaths similar to those shown by mortality statistics for the entire nation (Baron, et al. 1988). An updated evaluation of the representativeness of the 121 cities and the mortality patterns observed is currently underway. The Influenza Branch, National Center for Infectious Diseases, also relies on this system for timely estimates of the impact of epidemic influenza on mortality each influenza season.

^*122 cities are currently participating in the 121 Cities Mortality Reporting System.

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This page last updated June 25, 2004

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