Examination of Associations Between Zip Code Level COVID-19 Case Rates and Mental Health in Washington Counties among Young Adults

Background: Young adults have shown elevated levels of depressive and anxiety symptoms during the pandemic. However, few studies which have examined the impact of the COVID-19 pandemic on mental health have used area level COVID-19 case rates over time as a possible predictor for adverse outcomes. Method: The study sample included 382 participants residing in King, Snohomish, or Pierce County in zip codes with non-zero population counts, originally recruited from Project Transitions, a longitudinal study of young adults. Six bi-monthly surveys conducted from September/October 2020 through July/August 2021 used an 8-item measure for depressive symptoms, a 7-item measure for anxiety symptoms and a 12-item measure of flourishing. COVID-19 case rates were derived from positive cases per zip code from King, Pierce, and Snohomish Counties divided by estimated populations per zip code. Fixed effects models specifying a negative binomial or Gaussian distribution for the outcome were used to examine within-person associations between zip code COVID-19 prior month case rates per 1000 persons and mental health outcomes. Effect modification by sexual minority identity as well as by a dichotomized variable for financial strain was assessed using interaction terms. Results: For any given person occupying the same zip code, rate ratios for the PHQ-8 and GAD -7 score showed no association with zip code case rates (RR for PHQ-8 outcome = 1.00; 95% CI: -0.97, 2.97; and RR for GAD-7 outcome = 1.00; 95% CI: -0.97, 2.97). There was also no statistically significant association between zip code case rates and flourishing (β = 0.06; 95% CI: -0.12, 0.25). The association between zip code case rate and flourishing appeared to differ according to sexual identity, such that there was a negative association among those identifying as a sexual minority and a positive association among those not identifying as a sexual minority (interaction-p = 0.041). Conclusion: This study did not show associations between zip code level case rate and the mental health outcomes. However, secondary analyses suggest that the association between zip code case rates and flourishing was modified by sexual minority status. Addressing population wide inequities in mental health requires additional multilevel research to understand upstream drivers.