Background: Currently, CDC is restricted from re-releasing county-level STD case surveillance data stratified by demographics. Revision to the re-release guidelines based on a combination of denominator and disease proportion rules could maximize the amount of data released while maintaining a low risk of individual re-identification. We quantified the amount of county-level case report data that would be released using a denominator threshold of 100 or greater and a case proportion threshold of less than 10%.
Methods: We stratified 2010 county-level chlamydia, gonorrhea, and syphilis case report data by age, race, and sex. For each disease, we identified and suppressed all cells (i.e., county by age by race by sex categories) that had a denominator <100 or had a disease proportion >10%. We determined the percentage of total cells and cases suppressed by revised guidelines, stratified by urban/rural status. The need for secondary suppression (i.e., additional suppression so that back-calculation of suppressed cells is impossible) was explored.
Results: Applying the specified denominator and proportion rules, 17.3% of chlamydia cells (11.6% of cases), 9.1% of gonorrhea cells (1.5% of cases), and 2.3% of syphilis cells (0.9% of cases) would be suppressed. Suppression was greater in rural counties (e.g., 25.8% of chlamydia cells suppressed in rural counties versus 11.2% in urban counties). Additional cells would need to be suppressed secondarily, to avoid back-calculation of sensitive cells.
Conclusions: A denominator rule of 100 and a proportion rule of 10% would allow for the re-release of the majority of county-level STD case report data, increasing the utility of the data. However, secondary suppression rules are needed. Rural counties with small, homogenous populations are expected to contain more cells suppressed under these rules than larger, urban, racially diverse counties. More research into confidentiality protection measures at smaller geographic areas and more detailed variable stratifications are needed.