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 (RE ) 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 RE 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.

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加利福尼亚和华盛顿州2019年严重冠状病毒病的发病率，临床结局和传播动态：前瞻性队列研究。

目的了解在美国西海岸的第一次流行波期间，严重的冠状病毒病2019（covid-19）的流行病学和负担。设计前瞻性队列研究。设置Kaiser Permanente集成式医疗保健提供系统，服务于北加利福尼亚州，南加利福尼亚州和华盛顿州的居民。参与者到2020年4月22日，在9 596 321名医疗保健计划参与者中，有1840例首次入院确认为covid-19的急性患者。截至2020年4月9日的住院时间和临床结局分析包括1328人（加利福尼亚北部为534人，加利福尼亚南部为711人，华盛顿为83人）。主要观察指标：确诊covid-19的首次急性入院累积发生率，以及随后进入重症监护病房（ICU）的可能性和死亡率，以及住院时间和ICU住院时间。对于每个区域，估计描述传输动态的有效再现数（RE）。结果截至2020年4月22日，covid-19首次首次急性入院的累积发生率是：加利福尼亚北部每10万队列成员中有15.6人，加利福尼亚州南部每10万人中有23.3人，华盛顿州每10万中有14.7人。考虑到到2020年4月9日收治的住院病人不完整的住院检查，估计幸存者的平均住院时间为9.3天（95％的住院时间为0.8至32.9天），非幸存者的平均住院时间为12.7天（1.6至37.7天） 。男性患者接受ICU的审查调整概率为48.5％（95％置信区间41.8％至56。3％），女性患者为32.0％（26.6％至38.4％）。对于需要重症监护的患者，ICU住院时间的中位数为10.6天（其中95％的住院时间为1.3至30.8天）。男性住院患者的审查调整后病死率为23.5％（95％置信区间为19.6％至28.2％），女性患者为14.9％（11.8％至18.6％）。男性和女性患者的死亡风险都随着年龄的增长而增加。在每个区域的研究期内，确定了RE的减少。结论在参加了Kaiser Permanente医疗保健计划并以covid-19入院的加利福尼亚州和华盛顿州居民中，ICU入院，长期住院和死亡的可能性均很高。