Incidence, clinical outcomes, and transmission dynamics of severe coronavirus disease 2019 in California and Washington: prospective cohort study

Abstract

Objective

To understand the epidemiology and burden of severe coronavirus disease 2019 (covid-19) during the first epidemic wave on the west coast of the United States.

Design

Prospective cohort study.

Setting

Kaiser Permanente integrated healthcare delivery systems serving populations in northern California, southern California, and Washington state.

Participants

1840 people with a first acute hospital admission for confirmed covid-19 by 22 April 2020, among 9 596 321 healthcare plan enrollees. Analyses of hospital length of stay and clinical outcomes included 1328 people admitted by 9 April 2020 (534 in northern California, 711 in southern California, and 83 in Washington).

Main outcome measures

Cumulative incidence of first acute hospital admission for confirmed covid-19, and subsequent probabilities of admission to an intensive care unit (ICU) and mortality, as well as duration of hospital stay and ICU stay. The effective reproduction number ( R _E ) describing transmission dynamics was estimated for each region.

Results

As of 22 April 2020, cumulative incidences of a first acute hospital admission for covid-19 were 15.6 per 100 000 cohort members in northern California, 23.3 per 100 000 in southern California, and 14.7 per 100 000 in Washington. Accounting for censoring of incomplete hospital stays among those admitted by 9 April 2020, the estimated median duration of stay among survivors was 9.3 days (with 95% staying 0.8 to 32.9 days) and among non-survivors was 12.7 days (1.6 to 37.7 days). The censoring adjusted probability of ICU admission for male patients was 48.5% (95% confidence interval 41.8% to 56.3%) and for female patients was 32.0% (26.6% to 38.4%). For patients requiring critical care, the median duration of ICU stay was 10.6 days (with 95% staying 1.3 to 30.8 days). The censoring adjusted case fatality ratio was 23.5% (95% confidence interval 19.6% to 28.2%) among male inpatients and 14.9% (11.8% to 18.6%) among female inpatients; mortality risk increased with age for both male and female patients. Reductions in R _E were identified over the study period within each region.

Conclusions

Among residents of California and Washington state enrolled in Kaiser Permanente healthcare plans who were admitted to hospital with covid-19, the probabilities of ICU admission, of long hospital stay, and of mortality were identified to be high. Incidence rates of new hospital admissions have stabilized or declined in conjunction with implementation of social distancing interventions.

SciScore for 10.1101/2020.04.12.20062943: (What is this?)

Please note, not all rigor criteria are appropriate for all manuscripts.

Table 1: Rigor

Institutional Review Board Statement	not detected.
Randomization	not detected.
Blinding	not detected.
Power Analysis	not detected.
Sex as a biological variable	not detected.

Table 2: Resources

No key resources detected.

Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:

Our study has limitations. For this sample of 1277 hospitalized patients, we did not conduct a detailed review of medical records. As such, we do not address presenting characteristics of hospitalized patients and their association with demographic characteristics, length of hospital stay, or clinical outcome. Limited availability of laboratory testing in early phases of the US outbreak may have hindered ascertainment of sporadic cases in January and early February, 2020; because all persons under investigation for COVID-19 may not have received testing, our estimates of disease incidence should be interpreted as lower bounds. Near real-time hospitalization data may be missing for a modest subset of cases admitted to hospitals not owned by Kaiser Permanente, which would result in lagged reporting. In estimating transmission dynamics and cumulative infections, we relied on data from other settings to infer COVID-19 natural history parameters including the proportion of symptomatic infections requiring hospitalization, the serial interval, and the time from infection to hospitalization. Increases in the proportion of cases ascertained at later phases of the outbreak would be expected to increase RE estimates over time, contrary to the trend we observed. Last, our estimation of RE required an assumption that the KPNC, KPSC, and KPWA cohorts transmit among each other (or among epidemiologically similar individuals residing in the same areas). Within these regions, individuals rec...

Results from TrialIdentifier: No clinical trial numbers were referenced.

Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

Results from JetFighter: We did not find any issues relating to colormaps.

Results from rtransparent:

Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
No protocol registration statement was detected.

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