A preprint from April 12:
Title: Incidence, clinical outcomes, and transmission dynamics of hospitalized 2019 coronavirus disease among 9,596,321 individuals residing in California and Washington, United States: a prospective cohort
Lewnard, Liu, Jackson, Schmidt, Jewell, Flores, Jentz, Northrup, Mahmud, Reingold, Petersen, Jewell, Young, Bellows
Methods: We assessed incidence, duration of hospitalization, and clinical outcomes of acute COVID-19 inpatient admissions in a prospectively-followed cohort of 9,596,321 individuals enrolled in comprehensive, integrated healthcare delivery plans from Kaiser Permanente in California and Washington state. We also estimated the effective reproductive number (RE) describing transmission in the study populations.
Re is much the same as R0 unless you are getting toward herd immunity.
Results: Data covered 1277 hospitalized patients with laboratory- or clinically-confirmed COVID-19 diagnosis by April 9, 2020. Cumulative incidence of first COVID-19 acute inpatient admission was 10.6-12.4 per 100,000 cohort members across the study regions. Mean censoring-adjusted duration of hospitalization was 10.7 days (2.5-97.5%iles: 0.8-30.1) among survivors and 13.7 days (2.5-97.5%iles:
1.7-34.6) among non-survivors. Among all hospitalized confirmed cases,censoring-adjusted probabilities of ICU admission and mortality were 41.9% (95% confidence interval: 34.1-51.4%) and 17.8% (14.3-22.2%), respectively, and higher among men than women. We estimated RE was 1.43 (1.17-1.73), 2.09 (1.63-2.69), and 1.47 (0.07-2.59) in Northern California, Southern California, and Washington, respectively, for infections acquired March 1, 2020. RE declined to 0.98 (0.76-1.27), 0.89 (0.74-1.06), and 0.92 (0.05-1.55) respectively, for infections acquired March 20, 2020.
Conclusions: We identify high probability of ICU admission, long durations of stay, and considerable mortality risk among hospitalized COVID-19 cases in the western United States. Reductions in RE have occurred in conjunction with implementation of non-pharmaceutical interventions.
Funding: Kaiser Permamente
… Social distancing recommendations for vulnerable populations were issued in San Francisco on March 6, 2020, and large gatherings were banned in Washington on March 11. Large-scale stay-at-home orders were implemented March 17 for the six counties of the San Francisco Bay area, and statewide in California and Washington on March 19 and March 24, respectively….
To inform the epidemiology of COVID-19 in these regions, we analyzed healthcare data covering all hospitalized COVID-19 cases within the cohort of 9,596,321 individuals receiving comprehensive, integrated care from Kaiser Permanente (KP) healthcare systems in Northern California (KPNC), Southern California (KPSC), and Washington state (KPWA).
The KPNC, KPSC, and KPWA systems deliver fully integrated healthcare to diverse membership cohorts generally resembling the commercially-insured populations of the surrounding geographic areas. We analyzed clinical and administrative data captured from all KP members who had been hospitalized within these KP care delivery systems with COVID-19 laboratory or clinical diagnoses at any recorded healthcare encounter by April 9, 2020.
Available data for patients included dates of COVID-19 clinical encounters, patient age, sex, dates of hospitalization, total duration of hospital stay, duration of ICU stay, ultimate clinical disposition (for completed hospitalizations only), and COVID-19 diagnostic tests performed in any setting as well as test results. …
Retrospective reviews of de-identified administrative data for this study were considered exempt, nonhuman subjects research by the KPNC, KPSC, and KPWA institutional review boards.
Role of the funding source
The funder of the study played no role in study design, data collection, data analysis, data interpretation, or the writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication.
In total, 1277 members were hospitalized with confirmed COVID-19 diagnoses as of April 9, 2020, with 539, 664, and 74 belonging to the KPNC, KPSC, and KPWA cohorts, respectively (Table 1). The median age of cases across all three cohorts was 60 years
Same as in the UK: 60 year old median age for hospitalizations (not deaths).
, with a range of 1-103 years and 50% of patients between 47-72 years of age. Four (0.3%) patients were under 20 years of age, 505 (39.5%) were ages 65 years or older, and 157 (12.2%) were ages 80 years or older; 725 (56.8%) were male. Laboratory confirmation of COVID-19 diagnosis was available for 1171 (91.7%) hospitalized patients as of April 9, 2020.
Hospitalizations were complete for 817 (64.0%) individuals
36% were still in the hospital.
, among whom disposition data were complete for 772. Among all patents with completed hospitalizations and outcomes recorded, 119 (15.4%) were deceased by April 9, 2020. Data on ICU admission were available for 617 individuals (only those in the KPNC and KPSC cohorts), among whom 158 were admitted to ICU.
Incidence of COVID-19 hospitalization
For the period ending April 9, 2020, we estimated the cumulative incidence of COVID-19 hospitalization within the KPNC, KPSC, and KPWA cohorts to be 12.4, 14.6, and 10.6 per 100,000 individuals (Figure 1). Incidence increased with age, reaching 61.0, 55.2, and 37.4 hospitalizations per 100,000 individuals ages ≥80 years in each of the three regions, respectively.
… we estimated 41.9% (34.1-51.4%) probability of ICU admission and 17.8% (14.3-22.2%) probability of death. Risk of death generally increased with age, while risk of ICU admission and death each tended to be higher among male than female patients (Figure 3). Risk of ICU admission appeared to increase with age among men only, with estimates ranging from 44.6% (26.4-76.0%) at ages 20-29 years to 70.7% (48.2-100.0%) at ages 70-79 years.
… Our estimates of RE indicated that individuals acquiring infection on March 1, 2020 were expected to cause an average of 1.43 (1.17-1.73), 2.09 (1.63-2.69), and 1.47 (0.07-2.59) secondary cases in Northern California, Southern California, and Washington state, respectively. Those acquiring infection on March 20, were expected to cause 0.98 (0.76-1.27), 0.89 (0.74-1.06), and 0.92 (0.05-1.55) secondary infections in the same settings.
So R0 was slightly under 1.0 by March 20 on the West Coast. Is this in line with other numbers? Deaths in California keep going up, so I don’t know.
We estimated a mean interval of 13.5 days (4.8-27.9) between infection and hospitalization for cases that would ultimately be hospitalized (Table S3). Accounting for the ratio of total infections to hospitalized cases, and for censoring of infections not yet hospitalized, we estimated the cumulative incidence of infection within the KPNC, KPSC, KPWA cohorts was 2.2 (1.7-3.1), 3.0 (2.3-4.1), and 1.6 (1.2-2.2) per 1000 individuals as of April 3, 2020.
… It should be noted that our daily RE(t) estimates describe transmission resulting from infections acquired each day t, rather than those transmitting on each day t. Because most individuals begin transmitting >4 days after acquiring infection, declines in RE values are expected to precede dates of implementation of interventions that would affect transmission during individuals’ infectious periods. Individuals may have also taken precautionary measures to limit risk of acquiring or transmitting infection prior to implementation of stay-at-home orders.
… Within these regions, individuals receiving healthcare from KP
health plans may be wealthier than those without commercial insurance. Economic security and employment type may impact individuals’ ability to comply with stay-at-home orders, meaning our estimates of transmission dynamics may not describe circumstances for other populations, including socioeconomically vulnerable groups. Despite this limitation, our use of data on hospitalized cases in a prospectively-followed cohort, receiving care within a unified healthcare delivery system, overcomes inconsistencies affecting RE estimates from syndromic surveillance of milder COVID-19 cases across care providers and jurisdictions.30
The considerable length of stay among hospitalized cases in our study indicates that unmitigated transmission of SARS-CoV-2 poses a threat to US hospital capacity, consistent with observations in Italy and other high-resource settings3 as well as recent experience in New York. Our estimates of cumulative
infections suggest the western United States remains far from reaching a herd immunity threshold.