Los Angeles County SARS-CoV-2 Epidemic: Critical Role of Multi-generational Intra-household Transmission

Abstract

We tracked the course of the COVID-19 epidemic among the approximately 300 communities comprising Los Angeles County. The epidemic, we found, had three distinct phases. During Phase I, from early March through about April 4, initial seeding of infection in relatively affluent areas was followed by radial geographic extension to adjoining communities. During Phase II, which continued to about July 11, COVID-19 cases continued to rise at a slower rate, and became increasingly concentrated in four geographic foci of infection across the county. This phase saw changes in two indicators of social mobility: the proportion of location-tracked smartphones staying at home, and the number of smartphones visiting a gym. For both indicators, those communities with a larger reduction in social mobility during April reported fewer new COVID-19 cases in May. During Phase III, COVID-19 incidence only gradually declined, remaining as high as the incidence seen at the end of Phase I. Across communities, the prevalence of households at high risk for intergenerational transmission was strongly correlated with the persistence of continued COVID-19 propagation. This association was even stronger in those communities with a higher rate of gym attendance in Phase II. The map of the prevalence of at-risk households in Los Angeles County coincided strikingly with the map of cumulative COVID-19 incidence. These findings, taken together, support the critical role of household structure in the persistent propagation of COVID-19 infections in Los Angeles County. Public health policy needs to be reoriented from a focus on protecting the individual to a focus on protecting the household.

An integrated risk and epidemiological model to estimate risk-stratified COVID-19 outcomes for Los Angeles County: March 1, 2020—March 1, 2021

“…While this work has focused on demonstrating the substantial heterogeneity in risk probabilities and IFR across subpopulations, it employs a single-population epidemic model. LAC is a large county consisting of many composing cities and communities, each with their own epidemic processes unfolding at different rates [ 48 ]. Extreme disparities in infection incidence and mortality have been observed for different communities within LAC.…”

“…Future work will develop multi-population models that estimate subpopulation-stratified probabilities of infection, of illness progression, and IFR , accounting for key risk factors of both exposure to infection and severe illness given infection. Risk factors for exposure are not limited to age and health conditions, but also include more diverse socioeconomic factors including occupation and essential worker status, neighborhood of residence, housing overcrowding, multigenerational households, economic status, and access to PPE [ 48 – 52 ]. In the meantime, the subpopulation-stratified estimates of disease progression and IFR produced using the framework presented here can be used to evaluate policy decisions that may involve both population-wide interventions and interventions that target specific subpopulations at risk of developing severe illness given infection, for example isolating or prioritizing vaccination for the elderly or those with other health-related risk factors [ 16 ].…”

The Impact of Structural Inequities on Older Asian Americans During COVID-19

“…More than 20% of South Asian, Filipinx, and Vietnamese American older adults live in multigenerational homes ( Table 1 ). Physical and social distancing during the pandemic is especially difficult in crowded housing conditions, where there is increased risk of intra-household transmission of coronavirus ( 33 , 34 ), especially in households with high-risk older adults, frontline workers, and individuals without insurance. Although the national vaccination guidelines prioritized older adults, only a few states have flexed their plans to include prioritization for household members living with older adults to ensure adequate protection against intra-household COVID-19 transmission ( 35 ).…”

Geospatial Analysis of the September 2020 Coronavirus Outbreak at the University of Wisconsin – Madison: Did a Cluster of Local Bars Play a Critical Role?

“…The Social Distancing database provides information on both the origin and destination census block groups of device holders. We previously relied upon this data source in a study of the movements of individuals with a home in the Queens-Elmhurst COVID-19 hot spot to subway stations in Queens and Manhattan during the earliest days of the epidemic in New York 11City (Harris 2020e), and in the previously cited study of the role of intrahousehold transmission in the COVID-19 epidemic in Los Angeles County (Harris 2020i).…”

“…Even more broadly, we need to think about systemic factors that influence viral propagation, and not simply the characteristics of individuals or the places they go to. The epidemic in Los Angeles County has been sustained in great part by intra-household transmission among multigenerational families (Harris 2020i). But the larger question is what public policies have enhanced or mitigated these housing conditions.…”