Journal Pre-proof Systematic review of the associations of and density

5 Living in compact neighbourhoods that are walkable, well connected, with accessible green 6 space can benefit physical and mental health. However, the pandemic raises concern that 7 higher population density may increase transmission of Covid-19, leading some to question 8 the policy of high-density or 15 minutes neighbourhoods. We conducted a systematic review 9 to identify, appraise and synthesise evidence reporting associations between transmission of 10 respiratory viruses, including Covid-19, and dwelling or population density or other features 11 of neighbourhood design. Twenty-one studies met our inclusion criteria. These studies used 12 differing measures of neighbourhood design, and their findings were inconsistent. No clear 13 conclusion can be drawn about any association between compact neighbourhood design and 14 transmission of infection. 15

For each eligible study, we extracted data on details of the study (i.e., first author, year of 150 publication, study design, country, the period studied), neighbourhood (i.e., neighbourhood 151 setting, measures of neighbourhood environment), respiratory infectious disease (i.e., 152 infectious agents type, outcome measured) and main findings (i.e., analysis metric, effect 153 size, covariates included in the analysis). Data were extracted by two investigators 154 independently and any discrepancies agreed by consensus. 155 156

Data Synthesis 157
Due to heterogeneity, predominantly in exposure and/or outcome characteristics, we 158 conducted narrative analyses. We summarised and compared the neighbourhood and viral 159 respiratory infectious diseases characteristics of each eligible study. Subsequently, we 160 compared the above-mentioned characteristics after categorizing the studies into subgroups 161 based on countries, type of infectious diseases and different measures of a neighbourhood. 162 163

Quality and risk of bias assessment 164
Two team members appraised each study, with discrepancies in views resolved by consensus. 165 We applied the CASP checklists for cohort and case/control studies. For ecological studies, 166 we adapted a checklist originally from another review (Betran et al., 2015). The checklist 167 consisted of 14 items which included items regarding study design, statistical analysis 168 methods and quality of reporting (Table S1). We graded study quality using the Grades of

Study selection 177
The database searches identified a total of 2,743 articles. After removing duplicates and 178 including articles detected from citation tracking, 1,890 articles were screened. A total of 21 179 articles were eligible for inclusion in the systematic review (    Table 4 presents studies from countries other than the USA or China. There were only two 284 studies, both ecological. A study of Israeli residential communities (Birenbaum-Carmeli and 285 Chassida 2020) found a positive association between Covid-19 case rates and population 286 density, reporting that an increase of 100 persons per km 2 raised the Covid-19 case rate by 287 2.4 cases per 100,000 persons. The study found that population density was positively 288 associated with Covid-19 case rates in both Jewish and Arab communities. It also reported 289 the counterintuitive results that higher proportions of older people and lower socioeconomic 290 status were both statistically significantly associated with lower rates of Covid-19. The 291 authors suggested that this could be because large families with children increased spread of 292 infection. However, as they did not adjust for the child population in their analysis of 293 population density, this is difficult to assess. In addition, a UK study (Olowokure et al. 2003) 294 reported on haemophilus influenza type b (Hib) in children under 5 years in the West 295 Midlands, before and after the introduction of Hib vaccine in the 1990s. Both before and after 296 the vaccine, they found a statistically significant negative association with population density. 297 However, the analysis did not adjust for covariates and may be confounded by other factors. for other reasons, live in densely populated areas containing multi-unit buildings (Table 2). 312 Two studies from China considered associations between Covid-19 and building scale (You,313 Wu, and Guo 2020) or building height (Huang et al. 2020), which may indicate higher 314 housing density (Table 3) (Table 2). 318 319 Three studies, from USA or Hong Kong, considered associations with walkability, active 320 commuting or land use mix and reached conflicting results. The study of zip codes in 321 Chicago and New York (Credit, 2020) adjusted for covariates and found that zip codes with 322 higher levels of active commuting had lower rates of confirmed Covid-19 (Table 2). 323 However, the larger study of over 7,000 zip codes across 20 states found that indicators of 324 walkability and land use mix both increased the rate of Covid-19 and single lane roads 325 reduced the rate ( Table 2). The Hong Kong study ) found a negative 326 association between land use mix and confirmed Covid-19 cases (Table 3). 327 328 Three studies, in USA or China, considered associations with proximity to or density of 329 schools. A New York study (DiMaggio et al. 2020) found no statistically significant 330 association between Covid-19 incidence density ratio and school density ( Table 2). Two 331 studies from China (Table 3)  Three studies, all in China, studied the association with the density of, or distance to, 338 commercial facilities with inconsistent findings (Table 3) Rocklöv and Sjödin, 2020). Following this concern, we found that studies reported 364 conflicting findings on population and housing density. This could reassure urban designers 365 and policymakers who are promoting compact and walkable neighbourhoods in many 366 international cities, such as the 20-minute neighbourhood in Scotland (Scottish Government, 367 journeys more than those in lower density areas. Hamidi   Opinion pieces, modelling studies predicting infection transmission without new empirical data, qualitative studies and reviews (retained the latter two types of study for separate analysis and background)

Context
Studies based in high-/middle-income countries Studies based in low-income countries