Population Research Unit, Faculty of Social Sciences, University of Helsinki, Helsinki, Finland.
Helsinki Institute for Social Sciences and Humanities, University of Helsinki, Helsinki, Finland.
PLoS Med. 2022 Aug 10;19(8):e1004038. doi: 10.1371/journal.pmed.1004038. eCollection 2022 Aug.
Although intrahousehold transmission is a key source of Coronavirus Disease 2019 (COVID-19) infections, studies to date have not analysed socioeconomic risk factors on the household level or household clustering of severe COVID-19. We quantify household income differences and household clustering of COVID-19 incidence and severity.
We used register-based cohort data with individual-level linkage across various administrative registers for the total Finnish population living in working-age private households (N = 4,315,342). Incident COVID-19 cases (N = 38,467) were identified from the National Infectious Diseases Register from 1 July 2020 to 22 February 2021. Severe cases (N = 625) were defined as having at least 3 consecutive days of inpatient care with a COVID-19 diagnosis and identified from the Care Register for Health Care between 1 July 2020 and 31 December 2020. We used 2-level logistic regression with individuals nested within households to estimate COVID-19 incidence and case severity among those infected. Adjusted for age, sex, and regional characteristics, the incidence of COVID-19 was higher (odds ratio [OR] 1.67, 95% CI 1.58 to 1.77, p < 0.001, 28.4% of infections) among individuals in the lowest household income quintile than among those in the highest quintile (18.9%). The difference attenuated (OR 1.23, 1.16 to 1.30, p < 0.001) when controlling for foreign background but not when controlling for other household-level risk factors. In fact, we found a clear income gradient in incidence only among people with foreign background but none among those with native background. The odds of severe illness among those infected were also higher in the lowest income quintile (OR 1.97, 1.52 to 2.56, p < 0.001, 28.0% versus 21.6% in the highest quintile), but this difference was fully attenuated (OR 1.08, 0.77 to 1.52, p = 0.64) when controlling for other individual-level risk factors-comorbidities, occupational status, and foreign background. Both incidence and severity were strongly clustered within households: Around 77% of the variation in incidence and 20% in severity were attributable to differences between households. The main limitation of our study was that the test uptake for COVID-19 may have differed between population subgroups.
Low household income appears to be a strong risk factor for both COVID-19 incidence and case severity, but the income differences are largely driven by having foreign background. The strong household clustering of incidence and severity highlights the importance of household context in the prevention and mitigation of COVID-19 outcomes.
尽管家庭内传播是 2019 年冠状病毒病（COVID-19）感染的一个主要来源，但迄今为止的研究尚未分析家庭层面的社会经济风险因素或 COVID-19 的严重程度的家庭聚集情况。我们量化了家庭收入差异和 COVID-19 发病率和严重程度的家庭聚集。
我们使用基于登记的队列数据，在各种行政登记册中对居住在工作年龄私人家庭中的芬兰总人口（N=4315342）进行个体水平的链接。从 2020 年 7 月 1 日至 2021 年 2 月 22 日，从国家传染病登记册中确定了 COVID-19 病例（N=38467）。严重病例（N=625）的定义是至少有 3 天连续住院治疗，COVID-19 诊断为阳性，并在 2020 年 7 月 1 日至 2020 年 12 月 31 日期间从医疗保健护理登记册中确定。我们使用个体嵌套在家庭中的 2 级逻辑回归来估计感染人群中的 COVID-19 发病率和病例严重程度。在调整年龄、性别和区域特征后，与收入最高的五分位数（18.9%）相比，收入最低五分位数（OR 1.67，95%CI 1.58 至 1.77，p<0.001）的个体 COVID-19 发病率更高。但当控制外国背景等家庭层面的其他风险因素时，这种差异减弱（OR 1.23，1.16 至 1.30，p<0.001）。事实上，我们仅在具有外国背景的人群中发现了明确的发病率收入梯度，而在具有本国背景的人群中则没有。感染人群中患重病的几率也较高五分位数（OR 1.97，1.52 至 2.56，p<0.001，28.0% 与最高五分位数相比，21.6%），但当控制其他个体风险因素-合并症、职业状况和外国背景时，这种差异完全减弱（OR 1.08，0.77 至 1.52，p=0.64）。发病率和严重程度在家庭内高度聚集：发病率的约 77%和严重程度的 20%差异归因于家庭之间的差异。本研究的主要局限性是 COVID-19 检测率可能因人群亚组而异。
低家庭收入似乎是 COVID-19 发病率和病例严重程度的一个重要危险因素，但收入差异主要是由具有外国背景驱动的。发病率和严重程度的强烈家庭聚集突出了家庭环境在预防和减轻 COVID-19 结果方面的重要性。
