Social determinants of COVID-19 incidence and outcomes: A rapid review

Early reports indicate that the social determinants of health are implicated in COVID-19 incidence and outcomes. To inform the ongoing response to the pandemic, we conducted a rapid review of peer-reviewed studies to examine the social determinants of COVID-19. We searched Ovid MEDLINE, Embase, PsycINFO, CINAHL and Cochrane Central Register of Controlled Trials from December 1, 2019 to April 27, 2020. We also searched the bibliographies of included studies, COVID-19 evidence repositories and living evidence maps, and consulted with expert colleagues internationally. We included studies identified through these supplementary sources up to June 25, 2020. We included English-language peer-reviewed quantitative studies that used primary data to describe the social determinants of COVID-19 incidence, clinical presentation, health service use and outcomes in adults with a confirmed or presumptive diagnosis of COVID-19. Two reviewers extracted data and conducted quality assessment, confirmed by a third reviewer. Forty-two studies met inclusion criteria. The strongest evidence was from three large observational studies that found associations between race or ethnicity and socioeconomic deprivation and increased likelihood of COVID-19 incidence and subsequent hospitalization. Limited evidence was available on other key determinants, including occupation, educational attainment, housing status and food security. Assessing associations between sociodemographic factors and COVID-19 was limited by small samples, descriptive study designs, and the timeframe of our search. Systematic reviews of literature published subsequently are required to fully understand the magnitude of any effects and predictive utility of sociodemographic factors related to COVID-19 incidence and outcomes. PROSPERO: CRD4202017813.


Introduction
In the year since SARS-CoV-2 was identified in Wuhan, China the coronavirus disease 2019 (COVID-19) pandemic has resulted in more than 96 million cases and over 2 million related deaths [1]. Although COVID-19 was initially deemed a "great equalizer" given universal susceptibility to this novel virus [2], reports emerged in late March 2020 that COVID-19 morbidity and mortality disproportionately impacted groups made vulnerable by policies that create and reinforce health disparities [3][4][5][6].
Preliminary analyses from the United States, Canada and the United Kingdom reported high rates of COVID-19 infections, hospitalizations and mortality in geographic regions with high densities of low-income and crowded households, and in locations where a high proportion of individuals were racialized [7][8][9][10]. Early epidemiological studies from the United States found that African-Americans had the highest mortality rates of any group, with Native Americans close behind [11][12][13][14][15][16]. The United Kingdom's Office of National Statistics reported that Black males and females were respectively 4.2 and 4.3 times more likely to die from COVID-19, when compared to White individuals adjusting for age [17]. People in congregate settings, including prisons and homeless shelters, and long-term institutional care facilities also appeared to be at higher risk for infection and worse outcomes once infected [18][19][20].
Infection rates and outcomes for infectious diseases are influenced by social factors [21]. For example, during the 2009 H1N1 pandemic, incidence was highest among those without access to paid sick leave, and racialized individuals and those experiencing high material deprivation were more likely to be admitted to intensive care units [22][23][24]. While there is a growing recognition that social factors have similarly influenced COVID-19, the synthesis of relevant research is limited. Given that an empirical understanding of the broader social determinants of COVID-19 could inform ongoing pandemic response efforts, we conducted a rapid review of early reports on the social determinants of COVID-19 infection, health service use and health outcomes.

Data sources and searches
We designed this rapid review using interim guidance from the Cochrane Rapid Review Methods Group [25] and registered the review protocol with PROSPERO (CRD42020178131). We searched Ovid MEDLINE, Embase, PsycINFO, CINAHL and Cochrane Central Register of Controlled Trials bibliographic databases (S1 File) from December 1, 2019 to April 1, 2020, updating once on April 16, 2020, and again on April 27, 2020. We used a combination of search terms for SARS-CoV-2 and COVID-19. Database searches were supplemented with manual searches of bibliographies of included studies, COVID-19 evidence repositories and living evidence maps [26][27][28], and report referrals solicited from research colleagues (Australia, Belgium, Canada, China, United States and United Kingdom) with expertise in health equity and population health (S2 File). Experts were contacted by email and asked to forward reports that fit within our inclusion criteria. They were welcomed to forward our request to others within their network. We included studies identified through supplementary sources up to June 25, 2020.
included analyses of surveillance data published by public health agencies, and excluded modelling studies, secondary analyses, news items, opinions and editorials. Using emerging reports on how social factors impacted COVID-19 and the framework of the World Health Organization Commission on the Social Determinants of Health [29], we focused on studies that reported participant race or ethnicity, income, education, employment, housing status, food security, and social isolation (S1 Table). We excluded studies that only reported age and biological sex of participants, as these relationships are well-described elsewhere [30].

Data extraction and quality assessment
Data extraction was completed using a piloted form (S3 File) by two members of the study team (TLU and CB) and confirmed by another study team member (RS). We conducted quality assessment using the Mixed Methods Appraisal Tool (MMAT) [31]. The MMAT is a validated tool for appraising quality of quantitative randomized, quantitative non-randomized, quantitative descriptive, qualitative and mixed-methods studies included in mixed literature reviews [31,32].

Data synthesis and analysis
Given the heterogeneity of study designs, we did not conduct a pooled analysis and instead conducted a narrative synthesis [33,34]. We organized article findings by related social determinants of health, and then by study design within each determinant category. If studies addressed more than one determinant, we described them in multiple categories.

Results
Of 7,376 records screened, (Fig 1), 42 articles met our inclusion criteria (Table 1), 12 of which were identified through supplementary sources. These studies were conducted in China (13) and high-income countries, including Australia (2), Singapore (2), Spain (1), the United Kingdom (2), the USA (21), and a group of European Union member countries. They included cross-sectional (n = 19), cohort (n = 11), case series (n = 8) and case-control (n = 4) designs. Of included studies, 23 reported participant race or ethnicity data, 16 on occupation, 5 on income, 2 each on education and social isolation, 1 on food security and 6 on housing status.

Race or ethnicity
Twenty-three studies (55%) reported participant race or ethnicity data. Three large studies found statistically significant differences in COVID-19 infection incidence and hospitalization outcomes by race or ethnicity [35][36][37] [36]. In California, USA, a retrospective cohort study (n = 14,036 adults; 1,052 cases) found that non-Hispanic Black-identifying participants positive for COVID-19 were more likely to be admitted to hospital than non-Hispanic White-identifying participants after adjusting for age, sex, comorbidities and income (OR = 2.67, 95% CI: 1.30-5.47, p<0.01) [37].
Five studies involving bivariate analyses found no statistically significant differences in COVID-19 prevalence, clinical presentation, or outcomes across racial or ethnic groups [38][39][40][41][42]. A cross-sectional study of 305 people with COVID-19 admitted to hospitals in Georgia, USA, found that 83% identified as non-Hispanic Black (n = 247); however, compared to patients grouped as "other" race or ethnicity (including White, Asian, Hispanic and Pacific Islander; 17%, n = 50) there were no statistically significant differences in the proportions who received mechanical ventilation or died [42]. In a NYC, USA retrospective cohort study of patients with COVID-19 (n = 338), Toussie et al. did not find statistically significant differences in primary health outcomes of COVID-19 patients according to race or ethnicity [41]. The authors suggested, however, that Hispanic ethnicity was an independent predictor of having more severe chest x-ray findings among admitted patients (n = 145, OR = not reported, 95% CI: not reported, p = 0.03) [41].
Fifteen studies reported relative frequencies of participant race or ethnicity without testing for statistically significant differences in study outcomes [11, [43][44][45][46][47][48][49][50][51][52][53][54][55][56]; among these, most did not report comparisons with general population race or ethnicity demographics. Goyal et al studied the clinical characteristics of 393 COVID-19 patients from New York City, USA and found the majority of cases were non-White [52]. H. Sun et al described the race and ethnicity of 30 palliative COVID-19 patients in NYC, USA and found most were of Hispanic origin (66.7%) [50]. A case series from NYC found that, of 18 COVID-19 cases with cardiac events, 50% were Hispanic [55]. Notably, Laurencin and McClinton found that 17.2% of people infected with (n = 3141) and 14.4% of those dying from (n = 96) COVID-19 in Connecticut were Black. The authors remarked that these frequencies are higher than the proportion of the Connecticut population that identifies as Black (12%, n = NR), though tests of heterogeneity were not conducted [48].

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Social determinants of COVID-19 incidence and outcomes: A rapid review worked at the same supermarket [65]. Agricultural workers or farmers were represented in six Chinese studies of COVID-19 patients, with relative frequencies ranging from 7.7% to 54.6% [61,62,[64][65][66]73]. In bivariate analyses, Shi et al found differences in the proportion of people with mild and severe COVID-19 symptoms comparing agricultural, non-agricultural, retired and student occupational groups, with agricultural workers having the most severe cases (p<0.001) [73]. Among four studies examining COVID-19 clinical features and describing occupation of participants, two did not assess differences by occupation [61,62] and two found no statistically significant differences in the severity of symptoms by occupation [64,66]. In Wuhan, China, Chu et al reported that among 54 hospitalized medical staff with COVID-19, severe disease tended to be more common among those working in non-emergency clinical or non-clinical settings [57]. Wang X. et al found that 16 of 80 hospitalized frontline medical workers in Wuhan were "other" non-medical healthcare workers compared to doctors and nurses [63]. Blanco et al conducted a case series of five HIV positive patients in Spain and found that two patients were sex workers, one of whom was admitted to ICU [72]. In the USA, five CDC Morbidity and Mortality Weekly Reports present the prevalence of COVID-19 among employees of homeless shelters, correctional or detention facilities and meat processing facilities. For homeless shelter staff, 21.0% (8/38) of staff at three homeless shelters in King County, Washington were positive [70], and 11.0% (33/313) of staff at 19 homeless shelters in Boston, Seattle, San Francisco and Atlanta were positive [69]. For correctional or detention facility staff, a study by the CDC using data from 37 states reported 2,778 cases of COVID-19 among staff members, of whom 3% became hospitalized and 1.0% died [67]. Another CDC study on 46 correctional and detention facilities in Louisiana found 253 staff members were infected with COVID-19, 7.5% of whom were hospitalized and 1.6% died [68]. Dyal et al assessed the incidence of COVID-19 among workers in meat and poultry processing facilities in 19 states [71]. Of the 130,578 workers in 115 affected meat and poultry processing facilities, 3.0% tested positive (4,913 cases) and 0.4% died; the authors hypothesized that language barriers, overcrowded housing, overcrowded transportation and incentives to continue to work while ill limited effective infection control.

Income and socioeconomic status
Five studies reported on income or proxies for income. Two studies from the UK examined the association between socioeconomic status and positive COVID-19 case incidence. Hastie et al used the Townsend score to assess socioeconomic deprivation, which incorporates measures of unemployment, non-car ownership, non-home ownership and household overcrowding [35]. The authors found that higher socioeconomic deprivation predicted COVID-19 positive status in a multivariable logistic regression model (highest vs. lowest Townsend quintile OR = 1.89; 95% CI = 1.37-2.60; p <0.001). De Lusignan et al assessed socioeconomic deprivation using the English Index of Multiple Deprivation, which incorporates measures including income, employment, education, health, crime, barriers to housing and services and living environment [36]. In both univariate and multivariate analyses, people living in more deprived areas were more likely to test positive for COVID-19 (OR = 2.03, 95% CI: 1.51-2.71, p<0.0001).
Three studies reported associations between income factors and COVID-19 outcomes [35-37]. Azar et al found that COVID-19 patients in a California healthcare system with Medicaid or who were uninsured were more likely to be admitted to hospital compared to those with commercial insurance (Medicaid: OR = 2.13; 95% CI: 1.24-3.68, p<0.01; Self-Pay/Unknown: OR = 2.19; 95% CI: 1.03-4.36, p<0.05) [37]. The same study found COVID-19 patients residing in higher income neighbourhoods were less likely than those residing in lower income neighbourhoods to be admitted to hospital (High income, fourth quartile: OR = 0.55, 95% CI: 0.33-0.91, p<0.05; High income, Third quartile: OR = 0.24, 95% CI: 0.12-0.46, p<0.001). Two studies only described the income or insurance status of participants with COVID-19 without testing for associations or drawing comparisons to general population income demographics [42,74].

Social isolation
Two studies assessed factors related to social isolation. In a UK study of 3,802 adults tested for COVID-19, the odds of a positive test were lower in households with two to eight people, compared to single-person households in a univariate analysis (p<0.0001), but this was no longer statistically significant after adjusting for sociodemographic, lifestyle and health related factors [36]. One study examined social capital in relation to sleep quality and mental health outcomes among 170 adults in central China isolating at home following confirmed or suspected COVID-19, or a known exposure [74]. Social capital was measured using the Personal Social Capital Scale 16, scored according to number and professions of friends, relatives, coworkers; social trust; and civil society, recreational and political participation. After adjusting for potential confounders, higher social capital scores were significantly associated with lower anxiety and stress (structural equation model coefficients: anxiety, β = 0.619, p<0.001; stress, β = 0.327, p<0.001) [74].

Education
Two descriptive studies conducted in China examined education level of participants. Zhang et al surveyed 205 individuals to study mental health outcomes of populations affected by COVID-19 in Zhongshan [75]. Of the 57 individuals who reported having COVID-19, 30.9% had a junior-middle school education or less, 27.3% had a senior-middle school education and 41.8% had a college education or more. No statistically significant differences were observed by education level between patients who reported having COVID-19, were put under quarantine, or were non-infected members of the general public. The second study described the education level of 170 participants without examining differences in study outcomes [74].

Food security
One study by Li et al examined the association between malnutrition and COVID-19 prevalence in elderly hospitalized patients with COVID-19 in Wuhan, China [76]. Of 182 study participants, 52.7% were malnourished, 27.5% were at risk of malnutrition and 19.8% were nonmalnourished (p = 0.018). In their discussion, the authors reported that the level of malnourishment was higher in elderly COVID-19 patients than in elderly people with other health issues described by published literature.

Housing status
Six studies assessed housing-related factors among COVID-19 patient populations. Three descriptive studies and one cohort study from the USA examined COVID-19 incidence and outcomes among people experiencing homelessness. Tobolowsky et al studied a COVID-19 outbreak among three homeless services sites in King County, Washington and found a positive COVID-19 diagnosis in 35 of 195 residents (18%) tested [70]. Mosites et al assessed COVID-19 in 19 homeless shelters in Boston, Seattle, San Francisco and Atlanta [69]. Of the 1,292 shelter residents, 292 tested positive (25%). One shelter in San Francisco had 66% of 95 residents test positive. Baggett et al studied COVID-19 prevalence among homeless shelter residents in Boston and found that, of the 408 residents tested, 147 (36%) had a positive test result [77]. Among people testing positive for COVID-19 in California, Azar et al found no statistically significant association between homelessness and hospital admissions [37].
Two studies examined the incidence and outcomes of COVID-19 in correctional and detention facilities. We classified these as related to housing status because the authors describe the challenges of infection control within correctional facilities in relation to housing: crowded dormitories, shared bathrooms, limited medical resources, limited quarantine space and daily entry and exit of staff and visitors [67,68]. Wallace, Hagan et al examined national incidence of COVID-19 in 37 US jurisdictions that reported outcomes on correctional and detention facilities. Across 32 jurisdictions, 420 facilities had at least one case of COVID-19 [67]. They found 4,893 COVID-19 cases among incarcerated or detained persons, of whom 491 (10%) were hospitalized and 88 (2%) died. In a separate study of 144 correctional and detention Louisiana, Wallace, Marlow et al identified 489 laboratory-confirmed COVID-19 cases among incarcerated or detained persons, of which 47 (7.6%) were hospitalized and 10 (2%) died [68].

Quality assessment
The overall quality of included studies was low. Among the studies that involved comparison between people with or without COVID-19, or compared health outcomes among people with COVID-19, risk of selection and confounding biases were most common ( Table 2). This was most often due to the descriptive nature of analyses and small samples recruited over short periods of time, with limited information provided by authors to assist readers in evaluating the representativeness of samples. Eleven studies were at high risk of confounding (e.g. bivariate analyses), while seven had unclear risk of confounding (e.g. multivariable analyses accounting for sociodemographic, lifestyle and health-related confounders, but not other factors thought to be implicated in racial/ethnic differences in COVID-19 risk, such as employment in high-risk professions) [20, 38, 40, 54, 60, 62-64, 66, 74, 75]. Many of the case series or crosssectional studies also relied on small sample sizes and similarly had risk of selection bias ( Table 3); eight of these either provided insufficient detail for measurement methods for sociodemographic variable or outcomes, or insufficient detail of handling of missing data, and were therefore at risk of measurement error [11,44,48,52,57,67,71].

Discussion
In this rapid review we identified 42 peer-reviewed studies that included sociodemographic factors in analyses of COVID-19 incidence, clinical presentation, and prognosis. Most studies involved descriptive analyses, however more recent studies involving larger samples and multivariable analyses found key social determinants of health to be associated with COVID-19 incidence and outcomes. The strongest evidence of associations stems from three observational studies from the USA and UK which found associations between race and ethnicity, health insurance status, neighbourhood-level socioeconomic deprivation, and likelihood of COVID-19 positive status and COVID-19 hospital admission [35][36][37]. Limited evidence was available on other factors including occupation, educational attainment, housing status or food security.
While it remains possible that these associations could at least in part be explained by residual confounding and selection bias, the emergent findings are consistent with patterns observed during the H1N1 pandemic [22][23][24]. Adverse social conditions at the individual and community level, reinforced by systemic issues such as racism [78,79], may increase the likelihood of both COVID-19 infection and poor COVID-19 disease outcomes. Low-income

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Social determinants of COVID-19 incidence and outcomes: A rapid review earners are more likely to hold essential sales and service jobs and live in crowded housing conditions where ability to maintain physical distance from others is limited, increasing risk of virus exposure and transmission [10, [80][81][82]. Across studies and settings, labourers, retail staff, agricultural workers, healthcare workers and people working in congregate settings (shelters, correctional facilities, meat processing facilities) were reported to be over-represented among  [69,70,77]. This rapid review had several limitations. As with many rapid reviews, the short review timeframe, combined with the emergent nature of COVID-19 literature, limited the breadth of our analysis [83][84][85][86]. However, rapid reviews and full systematic reviews conducted on the same topic often produce similar conclusions [86]. Further, we screened all indexed English-language literature on COVID-19 published during the search period, ensuring we captured eligible studies. We did not address all social determinants of health, but focused on the ones that were likely most relevant to COVID-19 [87]. Our search extended only to April 27, 2020, with records identified through supplementary sources up until June 25, 2020. Small sample sizes, cohorts restricted to people testing positive for COVID-19, and the use of descriptive statistical methods limited the inferences that could be drawn from most of the early studies we reviewed. However, a number of studies published more recently have addressed these limitations.
Studies published since June 2020 tend to support our findings of disparities in COVID-19 infection, hospitalization, and mortality by race or ethnicity [88][89][90][91][92][93][94][95][96], socioeconomic status and deprivation [88-90, 92, 93, 97], and housing insecurity [95,96,98,99]. At least two recent studies did not find associations between race and mortality outcomes among those able to access hospital care [100,101], contrary to findings of most other research, including this review. More recent studies have also examined a wider range of sociodemographic factors in relation to COVID-19 infection such as primary spoken language [96], and additional studies have examined those factors less often assessed in early reports, such as educational attainment [90,93,97], occupation [97,102,103], and marital status [93]. Contrasting the early findings from one study included in our analysis, at least two studies indicate that cohabitation and larger households are associated with COVID-19 infection and mortality [103,104]. Food insecurity appears to remain an understudied factor in relation to COVID-19 incidence and outcomes. At the time of publication, we identified only one systematic review examining COVID-19 outcomes by ethnicity [105].
Among early reports, few studies collected data on the social determinants of health. Those that did were at high risk of bias and frequently had missing data was common, with incomplete or missing data for race or ethnicity reported by nineteen studies, with missing data ranging from 2.6% to 61% [11, 36-45, 48-54, 56]. To enhance availability of high-quality evidence for policymakers, we recommend that further large-scale prospective studies are complemented by knowledge sources from community health, social service and advocacy organizations. Studies initiated at the outset of future pandemics should endeavor to collect and asses individual-level data on social risk factors using standard tools, ensuring data collection, interpretation and subsequent actions taken are led by the communities most impacted. The literature on COVID-19 continues to expand rapidly [106], and future systematic reviews with meta-analyses will be required to fully understand the magnitude of any effects and predictive utility of sociodemographic factors related to COVID-19 incidence and outcomes.