key: cord-1028519-rm7q689v
authors: Malmgren, J.; Gou, B.; Kaplan, H. G.
title: COVID-19 Confirmed Case Incidence Age Shift to Young Persons Age 0-19 and 20-39 Years Over Time: Washington State March - April 2020
date: 2020-05-23
journal: nan
DOI: 10.1101/2020.05.21.20109389
sha: 2d703bf74fc405a145dfa7b0c44b29cd2a908756
doc_id: 1028519
cord_uid: rm7q689v

Background: As the coronavirus (COVID-19) epidemic passes the peak infection rate in some states and counties a phased re-opening with changes of stay-at-home restrictions and social distancing recommendations may lead to an increase of non-essential work, social activities and gathering, especially among younger persons. Methods: A longitudinal cohort analysis of Washington State Department of Health COVID-19 confirmed case age distribution March 1-April 19 2020 for proportional change over time using chi square tests for significance (N = 13,934). Results: From March 1st to April 19, 2020 age distribution shifted with a 10% decline in cases age 60 years and older and a 20% increase in age 0-19/20-39 years (chi-square = 223.10, p <.001). Number of cases over the eight-week analysis period were 0-19 years n = 515, 20-39 years n = 4078, 40-59 years n =4788, 60-79 years n = 3221, 80+ years n = 1332. New cases increased steadily among 0-19 and 20-39-year olds. After the peak (March 22, 2020), there was no decline among age 0-19 and a lesser decline among age 20-39 than older groups. As incidence declined in older age groups, the combined percentage of cases age 0-19 and 20-39 increased from 20% to 40% of total cases. Conclusions: Increased COVID-19 infection among children and young adults is not without serious morbidity and mortality risk to them and others they may come in contact with, indicating a targeted approach for awareness and safety measures is advisable to reduce incidence among the supposedly less vulnerable but more mobile young population age 0-19 and 20-39 years.

older age groups, the combined percentage of cases age 0-19 and 20-39 increased from 20% to 40% of total cases.

Conclusions: Increased COVID-19 infection among children and young adults is not without serious morbidity and mortality risk to them and others they may come in contact with, indicating a targeted approach for awareness and safety measures is advisable to reduce incidence among the supposedly less vulnerable but more mobile young population age 0-19 and 20-39 years.

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The 2019 novel coronavirus (COVID-19) has quickly spread over the globe and positive cases continue to climb. The first reported case of 2019-nCoV infection was in Washington State on January 19, 2020 and on March 23 rd , a statewide stay-athome order was announced to remain in effect until May 4 th which has been extended to May 30, 2020. 1,2 Change of stay-at-home restrictions and social distancing recommendations may lead to an increase of non-essential work, social activities and gathering, especially among younger persons. Using Washington State Department of Health (DOH) data, we analyzed incidence of COVID-19 cases by age for significant change in age distribution over time. As hospitalization rates declined and continued to decline but number of cases plateaued it became apparent age might be a factor to investigate to explain the changed presentation and severity of cases.

Testing of symptomatic patients for COVID-19 in Washington State has been steadily increasing since the outbreak began in January 2020 with drive-through testing beginning in some communities in late March thus increasing testing availability.

More than 25 labs in the state are now able to process COVID-19 testing. Total testing capacity statewide continues to change, which means each lab is the best source for current numbers on their own testing capacity. The results from all COVID-19 tests flow into the Washington Disease Reporting System (WDRS), an electronic disease surveillance system that allows public health staff in Washington . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint state to receive, enter, manage, process, track and analyze disease-related data.

Aggregate testing data is updated and published daily on the WA State DOH website with an update by age and county weekly.

We used the weekly updated COVID-19 positive confirmed case data from January 16 th to April 19 th , Washington State Department of Health (DOH), available to the public on their website with updated data added for trend in age distribution 4/26-5/3/2020. 3 The number of lab-confirmed COVID-19 cases from hospital, intensive care units, emergency departments and outpatient testing are reported by acute care hospitals in Washington daily. The data from DOH includes the number of cases, deaths and hospitalizations by week, county and age groups. Additional publicly available data on number of tests performed was also used in our study to address possible bias of changed testing by age over time. Our analysis used data updated May 3 2020 at 2 PM.

Laboratory-confirmed county-assigned cases by state assigned age groups 0-19, 20-39, 40-59, 60-79 and 80+ years in Washington State were enumerated and plotted over time. Statistical analyses were performed using Excel for percentage calculations and an online chi square calculator was used for two-sided significance testing with a .05 level of signficance. 4, 5 Weeks for analysis were restricted to March 1 to April 19 2020 when a sufficient number of cases (20 or more) had accrued to be statistically relevant and to accommodate the two-week lag time in case reporting and confirmation to WDRS. Age 0-19 was included even though there were only 4 cases in the first analysis week but case counts were greater than . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint 20 in following weeks. Chi-square tests were run comparing the first two weeks of increased cases (3/1/2020, 3/8/2020), the peak week (3/22/2020) and the most recent weeks (4/12/2020, 4/19/2020). Number of weeks were restricted to 3 groups and time from 3/1/2020 to 4/19/2020 to avoid the diminishment of statistical validity by multiple comparisons. doubling from 20% to 40%. Figure 1 . There was an increase in cases age 0-19 years over time from four cases week 3/1/2020 to 83 cases week 4/19/2020 and 131 week 5/3/2020. Incidence among age 60 and older declined 55% off peak but 20-39-year-old cases only declined 36% off the peak week (3/22/2020) and thereafter have remained relatively constant. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint [4/26/2020 (n=1554), 5/3/2020 (n=1210)] the age shift trend to age 0-19 and 20-39 was sustained over time to 50% of total cases. Table 1 is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint COVID-19 related hospitalization rates declined without an equivalent rate of decline among confirmed COVID-19 cases. The disproportionate rate of case hospitalization and confirmed case decline between older and younger age groups is concerning. The shift from from older to younger population COVID-19 infection may mask a true decline in cases and the need for future health care capacity if the currently infected portion of the population is younger, less likely to report symptoms, and at less risk of a severe life-threatening disease requiring hospitalization. In Seattle Washington 40% of the population is age 20-39 years old compared to 28% for the state and is located in the most populous county (King County 2019 population 2,252,782). 6 From our observations persons age 20-39 years old may be a specific group to target for infection control behavior modifications and directives as they are more often employed in work sectors with high levels of public contact.

As initial public warnings targeted the population age 60 and older and those with underlying conditions, a misconception may be at large that only persons age 60 and older are at risk for contracting COVID-19. Children have been thought to be at low risk for COVID-19 and if infected to have a mild clinical course with few or no symptoms. A health alert has been issued by the CDC for Pediatric Multisystem Inflammatory System (MIS-C) linked to COVID-19 indicating in some cases a low risk assessment may not be accurate. 7 The perception that age 0-19 and 20-39 age groups are not at high risk for morbidity and mortality from COVID-19 and thus might be free to interact with others discounts the possibility of asymptomatic . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint transmission and thereby endangers older adults and those with comorbid conditions they come in contact with. Younger persons may be more likely to participate in work and social activities that involve prolonged and intensive contact with others.

Findings from a recent survey by Canning et al, found persons under age 50 had twice the predicted number of close contacts than older people. 8

Limitations: While testing overall has increased during the period evaluated, the percentage of younger people being tested has decreased slightly compared to persons age 60 and older. Absent information to link family and household level data with parent's occupation to identify the source of exposure in the 0-19-year-old age group, one could assume the infections are driven by contact with family members working outside of the home as Washington State public schools have been closed since March 11, 2020.

The Washington State stay-at-home policy is temporally associated with the observed case decline after March 22, 2020. 9 Specific advisories to children and teenagers age 0-19 years and 20-39-year-old adults to increase awareness of COVID-19 transmission and infection among younger age groups may be advisable to reduce overall COVID-19 incidence levels and enhance movement towards levels that will allow phased reopening of the state and counties. 10

Our findings indicate a justifiable concern regarding the phased reopening plan for Washington State in late May in light of the shift in COVID-19 incidence from older to younger age with the majority of current cases now in the combined 0-19/20-39year-old age group. This specifically affects counties with a high percentage . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint population age 20-39 years. Continued tracking of age trends are warranted and will help target which activities can be opened and when that might occur. Going forward, younger persons with possible greater communicable capacity especially in King County could be included in the priority for identifying, controlling and stopping the spread of COVID-19. As Washington State is the first in the United States with COVID-19 experience and the longest outbreak timeline, our experience indicates analysis of incidence by age and county are useful tools for measuring outbreak progression.

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The copyright holder for this preprint this version posted May 23, 2020. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint All authors meet the conditions of authorship, 1) substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; 2) drafting the report or revising it critically for important intellectual content; and 3) final approval of the version to be published.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint Figures 1 and 2. 3/1/-4/19/2020 and 3/1-5/3/2020 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted May 23, 2020. . https://doi.org/10.1101/2020.05.21.20109389 doi: medRxiv preprint 

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