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Current Trends Update: Graphic Method for Presentation of Notifiable Disease Data -- United States, 1990

Since April 1990, data from the National Notifiable Diseases Surveillance System for 14 diseases have been published in a graphic format in the MMWR (Figure I, page 118) (1). The bar graph compares provisional reports for a 4-week period with the mean of 15 4-week totals (from the previous, comparable, and subsequent 4-week periods for the last 5 years) (2). Ratios that exceed national historical limits (calculated based on two standard deviations of the historical baseline) are indicated by striping in the bars. This report summarizes an evaluation of this new method.

To evaluate the method, state health departments provided supplemental information for diseases that exceeded historical limits during the first 6 months (April-September 1990) of publication of Figure I. For each interval in which a disease exceeded historical limits, the excess cases were usually accounted for by increased reports received from six or fewer states. The only exception was measles, which exceeded historical limits every 4-week period after April 21, 1990; increased measles activity was reported from most states (3).

Explanations for the increased number of reported cases of a given disease were readily available from most state health departments (Table 1); in some states, increased reports from multiple counties accounted for the increase, and no epidemiologic linkage was identified. Batch reporting of endemic or epidemic disease was often identified as a contributing factor in increased reports. For diseases with relatively small numbers of cases reported nationally (i.e., pertussis, legionellosis, and rubella), small increases in reporting caused totals to exceed historical limits. Many of the events reported by state health departments were small outbreaks; however, when aggregated with other nationally reported events, these outbreaks were sufficient to result in numbers exceeding historical limits. This method detected one ongoing outbreak of substantial public health importance in California; multiple outbreaks of rubella, primarily in unvaccinated adults, accounted for the increases in reporting (4). Reported by: CH Woernle, MD, State Epidemiologist, Alabama Dept of Public Health. L Dales, MD, GW Rutherford, III, MD, State Epidemiologist, California Dept of Health Svcs. R Hamm, MD, W Staggs, ML Fleissner, DrPH, State Epidemiologist, Indiana State Board of Health. DM Dwyer, MD, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene. T Pugliese, A DeMaria, MD, State Epidemiologist, Massachusetts Dept of Public Health. WN Hall, MD, MG Stobierski, DVM, KR Wilcox, Jr, MD, State Epidemiologist, Michigan Dept of Public Health. D Schneider, JK Gedrose, MN, State Epidemiologist, Montana State Dept of Health and Environmental Sciences. S Kondracki, DL Morse, MD, State Epidemiologist, New York State Dept of Health. E Bell, A Goodman, MD, City Epidemiologist, New York City Dept of Health. DR Tavris, MD, Pennsylvania Dept of Health. DM Simpson, MD, State Epidemiologist, Texas Dept of Health. Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs; Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases, Center for Infectious Diseases; Div of Surveillance and Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Limitations of routine national surveillance data for notifiable diseases have been described (5,6). However, follow-up of the graphic presentation of weekly surveillance data for 14 nationally notifiable diseases suggests that ongoing routine analysis of weekly provisional reports at the national level may detect changes from historical patterns that signal the need for public health intervention. Although the specificity of this method appears high, its sensitivity is unknown.

The method used to produce Figure I is not designed to detect all epidemics (2). Use of the previous 5-year average as the baseline for comparison may not detect all changes in disease reporting if large variations in disease case counts occurred during the baseline period. For example, the failure of the graphic method to demonstrate an increase in measles activity for the 4-week periods ending April 7-April 21 was due to increased measles activity during the baseline period used for comparison. In addition, outbreaks at the state or local level may be obscured when combined with other reports. The extent to which this occurred during April-September 1990 is unknown; however, preliminary information from a pilot project in progress suggests that the same analytic approach at the state level may be useful (CDC, unpublished data).

References

  1. CDC. Changes in format for presentation of notifiable disease report data. MMWR 1990;39:234.

  2. CDC. Proposed changes in format for presentation of notifiable disease report data. MMWR 1989;38:805-9.

  3. CDC. Measles--United States, 1989 and first 20 weeks 1990. MMWR 1990;39:353-5,361-3.

  4. CDC. Increased incidence of rubella and congenital rubella syndrome--United States, 1988- 1990. MMWR 1991;40:93-9.

  5. Sacks JJ. Utilization of case definitions and laboratory reporting in the surveillance of notifiable communicable diseases in the United States. Am J Public Health 1985;75:1420-2.

  6. Thacker SB, Berkelman RL. Public health surveillance in the United States. Epidemiol Rev 1988;10:164-90.



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