To the Editors:
The current perception of the rising SARS-CoV-2 prevalence attributes much of the ongoing transmission to younger individuals,1 in part driven by lower mortality rates recently compared with earlier in the pandemic2 and an increase in cases upon reopening schools.3 Such a narrative leads some to conclude that schools should remain closed and that public health interventions should be geared toward youth. With limited time and resources available to public health officials, it is imperative that our interventions be targeted toward those groups most at risk. Thus, we aimed to characterize the proportion of SARS-CoV-2 cases in Los Angeles by age group to evaluate if in fact young adults are a predominant group driving the surge in cases and therefore warranting heightened restrictions.
We evaluated SARS-CoV-2 test results from a large testing program in Los Angeles, California, between May and December 2020. Individuals presented to one of 250 drive-through testing facilities. Testers were required to complete an online survey that collected demographic information as well as the report of symptoms and other exposure risks.
We analyzed 2,582,635 test results. Since September 28, the week when the weekly positivity rate was at its lowest, the number of positive cases among individuals age 18–34 years increased 2216% (Fig. 1A). The weekly positivity rate for the week of September 28 was 1145 cases per week, while for the week of December 7, the positivity rate was 14,128 cases per week. However, the proportion of individuals who tested positive between the age of 18–34 years has not changed significantly over the course of the pandemic (Fig. 1B); for the week of September 28, 44.0% of cases were among 18–34 years, compared with 40.9% for the week of December 7. Similarly, when normalizing by the population size for each age group to account for variability in testing frequencies, for the week of September 28, 35.3% of the weekly positive tests were among 18–34 years olds, compared with 32.5% for the week of December 7.
Those findings imply that while there are an increasing number of cases among young individuals, the rate of increase is proportional to the overall increase in cases among the general population. Thus, younger individuals may not be the driving force behind the ongoing increase in cases. Such a finding may constitute a frame-shift in how we conceptualize the continued transmission of SARS-CoV-2 infection.
Prior studies have identified sub-populations that suffer a disproportionate burden of infection, such as individuals of lower socioeconomic status, minority races, and ethnicities,4 and residents of long-term care facilities.5 Those populations will likely benefit more from targeted public health interventions than will young adults. While our data are from a single geographic area, the large sample size lends credence to our results. Further research is needed to accurately characterize the specific exposures within those sub-populations that drive new infections. In the meantime, efforts to minimize the impacts of SARS-CoV-2 infection should focus on those most susceptible and at highest risk for serious complications.
The authors would like to acknowledge the City of Los Angeles. The Mass General Brigham institutional review board deemed the analysis of deidentified data did not constitute human subjects’ research (2020P003530).
1. Venkatesan P. The changing demographics of COVID-19. Lancet Respir Med. 2020; 8:e95.
2. Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19). Available at: https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/index.html
. Accessed November 18, 2020.
3. Grech V, Grech E, Borg Myatt J. Holidays over: a review of actual COVID-19 school outbreaks up to September 2020 [published online ahead of print October 1, 2020]. Early Hum Dev. 2020105206. doi:10.1016/j.earlhumdev.2020.105206.
4. Vijayan T, Shin M, Adamson PC, et al. Beyond the 405 and the 5: geographic variations and factors associated with SARS-CoV-2 positivity rates in Los Angeles County [published online ahead of print November 3, 2020]. Clin Infect Dis. 2020;ciaa1692. doi:10.1093/cid/ciaa1692.
5. Kaiser Family Foundation. State reports of long-term care facility cases and deaths related to COVID-19 (as of October 16, 2020). Available at: https://www.kff.org/health-costs/issue-brief/state-data-and-policy-actions-to-address-coronavirus/#top
. Accessed October 17, 2020.