Individual and social determinants of SARS-CoV-2 testing and positivity in Ontario,Canada: a population-wide study

BACKGROUND:Optimizing the public health response to reduce the burden of COVID-19 necessitates characterizing population-level heterogeneity of risks for the disease. However, heterogeneity in SARS-CoV-2 testing may introduce biased estimates depending on analytic design. We aimed to explore the potential for collider bias in a large study of disease determinants, and evaluate individual, environmental and social determinants associated with SARS-CoV-2 testing and diagnosis among residents of Ontario, Canada.METHODS:We explored the potential for collider bias and characterized individual, environmental and social determinants of being tested and testing positive for SARS-CoV-2 infection using cross-sectional analyses among 14.7 million community-dwelling people in Ontario, Canada. Among those with a diagnosis, we used separate analytic designs to compare predictors of people testing positive versus negative; symptomatic people testing positive versus testing negative; and people testing positive versus people not testing positive (i.e., testing negative or not being tested). Our analyses included tests conducted between Mar. 1 and June 20, 2020.RESULTS:Of 14 695 579 people, we found that 758 691 were tested for SARS-CoV-2, of whom 25 030 (3.3%) had a positive test result. The further the odds of testing from the null, the more variability we generally observed in the odds of diagnosis across analytic design, particularly among individual factors. We found that there was less variability in testing by social determinants across analytic designs. Residing in areas with the highest household density (adjusted odds ratio [OR] 1.86, 95% confidence interval [CI] 1.75–1.98), highest proportion of essential workers (adjusted OR 1.58, 95% CI 1.48–1.69), lowest educational attainment (adjusted OR 1.33, 95% CI 1.26–1.41) and highest proportion of recent immigrants (adjusted OR 1.10, 95% CI 1.05–1.15) were consistently related to increased odds of SARS-CoV-2 diagnosis regardless of analytic design.INTERPRETATION:Where testing is limited, our results suggest that risk factors may be better estimated using population comparators rather than test-negative comparators. Optimizing COVID-19 responses necessitates investment in and sufficient coverage of structural interventions tailored to heterogeneity in social determinants of risk, including household crowding, occupation and structural racism.

The spread of SARS-CoV-2, the virus causing COVID-19, has resulted in a pandemic with heterogeneity in exposure and risk of transmission.^1–4Heterogeneity in social determinants of COVID-19 may exist at the individual and community (e.g., by housing density^5–7) levels. In addition, social determinants of health, including barriers to health care, occupation, structural racism and xenophobia, have been implicated in COVID-19 risk.^8,9 Environmental determinants such as ambient air pollution may also play a role, as evidence indicates that higher ambient air pollution increases risk for infection with other respiratory viruses^10,11 and the development of severe COVID-19.^12,13 Environmental factors are linked with structural racism (e.g., in the context of low-quality housing).^12,14Using observational data to identify risk factors for COVID-19 relies on SARS-CoV-2 testing, a service that is not equally distributed.¹⁵ Differential testing introduces the potential for selection biases,^16,17 including collider bias.¹⁷ Collider bias may be introduced into epidemiologic studies of COVID-19 risk factors if the factors under investigation are related both to developing an infection and to the likelihood of being tested.^17–19 For example, data suggest that people with diabetes are more likely to develop severe COVID-19 if infected with SARS-CoV-2.^20,21 Thus, if infected, people with diabetes may be more likely to be tested, and consequently, diabetes may appear to be associated with a diagnosis of COVID-19 in studies of those tested for SARS-CoV-2, even if diabetes is not a risk factor for infection.¹⁷ The opposite may occur with underlying respiratory diseases (e.g., asthma) that have symptoms similar to those caused by SARS-CoV-2, leading to the appearance of potentially “protective” associations with COVID-19.²²Our objectives were to explore the potential for collider bias in a large study of COVID-19 determinants and examine individual, environmental and social determinants associated with testing and diagnosis among 14.7 million people in Ontario, Canada.¹⁷     

Potential for biofilms as biological indicators in Australian riverine systems

Summary Biological indicators have been widely used in Australian riverine systems to assess the effectiveness of past and current management. The short generation time, sessile nature, responsiveness to environmental conditions and the availability of sound, quantitative methodologies make biofilms suitable as a monitoring tool in these systems. This paper describes biofilm structure, function and development through the processes of succession and disturbance. Biofilms are assemblages of algae, fungi and microorganisms which cover rocks, wood and sediments in aquatic systems. A review of biofilm collection and processing techniques using relevant Australian and international studies reveals a large literature on many structural and functional biofilm attributes. Studies using structural attributes such as biomass and diversity to examine water quality impacts and invertebrate grazers dominate the Australian literature. More recently, studies have used functional biofilm attributes such as metabolism and foodweb interactions. Monitoring programs that combine structural and functional biofilm attributes will allow the best assessment of impacts in riverine systems. Biofilm functional parameters provide an integrated, long-term measure of ecosystem function, with structural attributes such as biomass and diversity allowing historical comparisons with previously recorded datasets. Monitoring programs such as these with a well-founded scientific base and defined management outcomes will expand our knowledge of river function and contribute to the restoration of Australian river systems.     

Vacuolar Reticulum in Oomycete Hyphal Tips: An Additional Component of the CaRegulatory System?

Cultures ofAchlyasp.,Phytophthora cinnamomi, Saprolegnia diclina, S. ferax,andS. parasitica,treated with 6-carboxyfluorescein diacetate solution, accumulate 6-carboxyfluorescein in a reticulate system of fine tubules. The network shows longitudinal polarity within the hyphae, tubules being finest toward the hyphal tips. In more mature subapical regions the network is connected with large vacuoles that also accumulate 6-carboxyfluorescein. A morphologically similar system has also been identified in freeze-substituted hyphae ofS. ferax.The network is considered to be vacuolar, but differs from the tubular vacuole system of true fungi in that tubules are less motile, more frequently branched, and do not alternate with clusters of spherical vacuoles. The appearance of the network resembles patterns of calcium-sensitive dye staining and it is suggested that the vacuolar reticulum in the tip region of oomycete hyphae may act as a Ca²⁺sink. The tubular reticulum in oomycetes is very fragile and can be shown with 6-carboxyfluorescein in only those hyphal tips with a motility and organelle distribution characteristic of growing hyphae with normal morphology. Diverse abnormal hyphae show a range of other fluorochrome localizations. These include large irregular compartments filled with fluorochrome, and fluorescent cytoplasm with organelles and vacuoles standing out in negative contrast. These localizations in abnormal hyphae are correlated with other structural changes indicative of damage. Special care is required in experiments with oomycetes to avoid such artefacts of localization.     

Pressure Induced Reorientation of Cortical Microtubules in Epidermal Cells of Lolium rigidum Leaves

In order to assess the effect on microtubule arrays of slowlypressurising cells over 50 s from 0.1 MPa (atmospheric pressure)to 55 MPa, microtubules in epidermal cells of Lolium rigidumleaves were visualised by immunofluorescent staining and fluorescencemicroscopy. In both control and pressure-treated leaves cellshape, measured as the ratio of cell length and width, can becorrelated to the arrangement of cortical microtubules. Microtubulearrays change from random to organised in cells whose lengthis greater than their width. In untreated leaves, elongatedcells have microtubules aligned predominantly transversely.In pressure-treated leaves, elongated cells have microtubulesaligned predominantly longitudinally. Thus, pressure treatmentresults in the rapid reorientation of organised cortical microtubulesfrom a transverse to a longitudinal orientation. (Received June 21, 1993; Accepted July 15, 1993)     

Specialized Transducing Phages Derived from Phage P22 That Carry the proAB Region of the Host, SALMONELLA TYPHIMURIUM: Genetic Evidence for Their Structure and Mode of Transduction

Two independently isolated specialized transducing phages, P22 pro-1 and P22pro-3, have been studied. Lysates of P22pro-1 contain a majority of transducing phages which can go through the lytic cycle only in mixed infection; these defective phages transduce by lysogenization in mixed infection and by substitution in single infection. A few of the transducing phages in P22pro-1 lysates appear to be non-defective, being able to form plaques and to transduce by lysogenization in single infection. Transduction by P22pro-3 lysates is effected by non-defective transducing phages, which transduce by lysogenization; these lysates also contain a majority of defective phages which do not co-operate in mixed infection.

The P22 pro-1 genome is thought to contain an insertion of bacterial DNA longer than the terminal repetition present in P22 wild type, so that at maturation a population of differently defective phages is produced. The exact structure of the P22pro-3 genome is open to conjecture, but it seems clear that the insertion of bacterial DNA is smaller than that in P22pro-1. Both P22pro-1 and P22pro-3 are defective in integration at ataA under non-selective conditions, although both integrate on medium that lacks proline.