No abstract

Background: Canada's nationwide lockdown to curb coronavirus disease 2019 (COVID-19) infections affected many sectors of activity, including universities. During the 2020-2021 academic year, all students were forced to follow their lectures from home and the only inperson activity permitted to Québec university level students was to study in designated spaces of campus libraries where COVID-19 preventive measures were in place and mandatory at all times for all staff and students. The objective of this study is to evaluate university-level students' compliance with COVID-19 preventive measures in a Québec campus library.Methods: A direct in-person evaluation by a trained observer was put in place to assess students' compliance with COVID-19 preventive measures defined as proper mask wearing and 2 meter distancing. Measurements were made each Wednesday, Saturday, and Sunday at 10 a.m., 2 p.m., and 6 p.m. from March 28 to April 25, 2021, in a university library in Québec, Canada.Results: Students' compliance with COVID-19 preventive measures was high overall (78.4%) and increased over the weeks, with differences between weeks, weekdays, and time of day. Non-compliance was lower on weeks three and four of the assessment compared with week one, and higher on Sunday compared with Wednesday. Differences seen throughout the day were not statistically significant. Non-compliance with physical distancing was rarely seen. Conclusion:Most university-level students are compliant with COVID-19 preventive measures in a Québec university library: an encouraging behaviour from a public health perspective. These findings may support public health authorities or university administrators in decisions regarding different COVID-19 preventive measures directed to different universities settings, as this method can be applied to focused, rapid observational studies and can lead to data of sufficient statistical power.

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e12614 Background: Tumor infiltrating lymphocytes (TILs) have been associated with good prognosis and response to neoadjuvant chemotherapy. Several reports have shown that the heterogeneity of tumor infiltrating immune cells affects the response to chemotherapy, with for example low levels of FOXP3 expressing T cells associated with good prognosis and pathological complete response (pCR) to chemotherapy. Methods: We examined different immune cell markers on 52 pre-chemotherapy biopsy specimens obtained from triple negative breast cancer patients undergoing neo-adjuvant chemotherapy from the Q-CROC-03 trial. Slides were stained for CD8, CD3,PD-1, PDL-1, FOXP-3 and Granzyme B using multi-colour immunohistochemistry and automated cell counting of stroma and epithelial counts was conducted using the Vectra/inForm image analysis platform. We had total of 39 variables for analysis and we performed Penalized logistic regression for variable selection. Results: Nine variables were found statistically significant to predict response to chemotherapy, PD1+ stroma counts being the one with the highest probability of association with response. A tree algorithm was then used on all 9 variables to identify the best variable and threshold combination to identify patients who respond to chemotherapy. We separated our cohort in test (25% of samples n = 13) and training (75% of samples n = 39) sets for this analysis. Restricting the tree depth to 2 variables for clinical interpretability identified the combination of average counts of stromal PD1+ and average density of stromal FOXP3+ as predictors of chemo response (accuracy 0.82). Both stromal average PD1+ counts and average stromal FOXP3+ density positively correlated with the levels of TILS. Conclusions: Combining FOXP3 and PD1 protein expression in the stroma of pre-treatment biopsies of triple negative breast cancers receiving neoadjuvant chemotherapy is highly predictive of pCR.