BACKGROUND: Improving readiness for infectious disease outbreaks at the local level is a complex endeavor involving preparedness components within healthcare systems and public health agencies. Community vulnerabilities, including population-level health burdens and sociodemographic characteristics, may increase the degree of preparedness needed, while the robustness of social safety net systems may help mitigate the impacts of communicable disease outbreaks among the most vulnerable populations. California is the most populous state in the U.S., with diverse metropolitan and rural communities. Additionally, public health authority in California is delegated to local jurisdictions, which can lead to differences in preparedness at the county level. We developed a county-level index to assess preparedness for infectious disease outbreaks among California counties.

METHODS: We integrated data from multiple private (e.g., National Association of County and City Health Officials, American Hospital Association, Public Health Accreditation Board, etc.) and public (e.g., Federal Emergency Management Agency, Supplemental Nutritional Assistance Program, Behavioral Risk Factor Surveillance System, California Department of Public Health, American Community Survey, etc.) data sources to develop the Community Outbreak Preparedness Index (COPI). COPI scores include measures of preparedness among four domains: Healthcare Systems; Public Health; Access to Safety Net Services; and Community Resilience (measured using CDC’s ATSDR Environmental Justice Index). Directionality of indicators was modified as needed so that higher values signify better preparedness. Indicators were equally weighted and averaged into domains, which were then averaged into a final score. Scores were scaled from 0 to 10 for ease of interpretability, with higher scores denoting better preparedness for future disease outbreaks. We used chi-squared and independent t-tests to explore the characteristics of the lowest scoring (bottom quartile) counties in California compared to the remaining counties.

RESULTS: The COPI average score among California counties (N=58) was 6.61, with scores ranging from 4.94 to 7.65, on a 10-point scale. Averages (with ranges) for each subdomain were 6.33 (3.97-7.89) for Healthcare System Preparedness, 4.90 (3.48-6.55) for Public Health Preparedness, 7.49 (7.17-7.86) for Access to Safety Net Services, and 7.75 (0-10) for Community Resilience. On average, compared to the rest of the state, the lowest scoring counties had populations that were significantly younger (below 19 years; 27.7% vs. 23.2%, p<0.01), more likely to have less than a high school education (21.8% vs 13.3%, p<0.01), and had greater proportions of people of Hispanic ethnicity (42.3% vs 28.1%, p=0.05). No differences were found in terms of distribution of sex, race, or urbanicity.

CONCLUSION: Our index provides a quantitative assessment of the numerous facets that contribute to community preparedness for an infectious disease outbreak, which can support decision-making, advocacy, and intervention development among stakeholders operating at all levels. Future analyses will explore associations between index scores and specific health outcome measures to inform wellness and preparedness efforts, particularly among vulnerable populations.