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International audience; This article analyzes the consequences of the increasing reference to scientific expertise in the decision and implementation process of occupational health policy. Based on examples (exposure limits and attributable fractions) taken from an interdisciplinary seminar conducted in 2014 to 2015 in France, it shows how the measurement or regulation of a problem through biomedicine-based tools produces blind spots. It also uses a case study to show the contradictions between scientific and academic aims and public health intervention. Other indirect implications are also examined, such as the limitation of trade unions’ scope for action. Finally, the article suggests launching a broad political debate accessible to nonspecialists about collective occupational health issues—a dialogue made difficult by the rise of the afore-mentioned techno-scientific perspective.

This study aims to describe the socio-demographic profile of so-called “key workers” during the first lockdown in France and to assess their potential occupational exposure to SARS-CoV-2 under routine, pre-pandemic working conditions. We used the French list of essential jobs that was issued during the first lockdown to identify three subgroups of key workers (hospital healthcare, non-hospital healthcare, non-healthcare). Based on the population-based “Conditions de travail-2019” survey, we described the socio-demographic composition of key workers and their potential work-related exposures (to “infectious agents,” “face-to-face contact with the public,” and “working with colleagues”) using modified Poisson regression. In general, women, clerical and manual workers, workers on temporary contracts, those with lower education and income, and non-European immigrants were more likely to be key workers, who accounted for 22% of the active population. Non-healthcare essential workers (57%) were the most socially disadvantaged, while non-hospital healthcare workers (19%) were polarized at both extremes of the social scale; hospital healthcare workers (24%) were intermediate. Compared to non-key workers, all subgroups had greater exposure to infectious agents and more physical contact with the public. This study provides evidence of accumulated disadvantages among key workers concerning their social background, geographical origin, and potential SARS-CoV-2 exposure.

ObjectiveAlthough social inequalities in COVID-19 mortality by race, gender and socioeconomic status are well documented, less is known about social disparities in infection rates and their shift over time. We aim to study the evolution of social disparities in infection at the early stage of the epidemic in France with regard to the policies implemented.DesignRandom population-based prospective cohort.SettingFrom May to June 2020 in France.ParticipantsAdults included in the Epidémiologie et Conditions de Vie cohort (n=77 588).Main outcome measuresSelf-reported anosmia and/or ageusia in three categories: no symptom, during the first epidemic peak (in March 2020) or thereafter (during lockdown).ResultsIn all, 2052 participants (1.53%) reported anosmia/ageusia. The social distribution of exposure factors (density of place of residence, overcrowded housing and working outside the home) was described. Multinomial regressions were used to identify changes in social variables (gender, class and race) associated with symptoms of anosmia/ageusia. Women were more likely to report symptoms during the peak and after. Racialised minorities accumulated more exposure risk factors than the mainstream population and were at higher risk of anosmia/ageusia during the peak and after. By contrast, senior executive professionals were the least exposed to the virus with the lower rate of working outside the home during lockdown. They were more affected than lower social classes at the peak of the epidemic, but this effect disappeared after the peak.ConclusionThe shift in the social profile of the epidemic was related to a shift in exposure factors under the implementation of a stringent stay-at-home order. Our study shows the importance to consider in a dynamic way the gender, socioeconomic and race direct and indirect effects of the COVID-19 pandemic, notably to implement policies that do not widen health inequalities.

Background There is a dearth of evidence on what should be the optimal criteria for discharging children from severe acute malnutrition (SAM) treatment. Programs discharging children while they are still presenting varying levels of weight-for-height (WHZ) or mid-upper-arm circumference (MUAC) deficits, such as those implemented under the current national protocol in Nepal, are opportunities to fill this evidence gap. Methods We followed a cohort of children discharged as cured from SAM treatment in Parasi district, Nepal. Relapse as SAM, defined as the occurrence of WHZ Results Relapse as SAM during follow-up was observed in 33 % of the cohort (35/108). Being discharged before reaching the internationally recommended criteria was overall associated with a large increase in the risk of relapse (HR = 3.3; p = 0.006). Among all anthropometric indicators at discharge, WHZp = 0.003), while MUAC p = 0.01), even among children with a MUAC ≥ 125 mm. Of note, more than 80 % of the events of relapse as SAM would have been missed if WHZ had not been monitored and used in the definition of relapse. Conclusions Our results suggest that the priority for SAM management programs should be to ensure that children reach a high level of WHZ at discharge, at least above or equal to the WHO recommended cut-off. The validity of using a single MUAC cut-off such as 125 mm as a suitable discharge criterion for all age groups is questioned. Further follow-up studies providing a complete assessment of nutritional status at discharge and not based on a restricted MUAC-only definition of relapse as SAM would be urgently needed to set evidence-based discharge criteria. These studies are also required to assess programs currently discounting or omitting WHZ for identification and management of SAM.

International audience; Background - In occupational epidemiology, a male-centered perspective often predominates. We aimed to describe current research practices in terms of gender consideration at different stages of epidemiological studies. Methods - A systematic review of occupational lung cancer publications indexed in PubMed was conducted over the period 2003-2014. Articles were described according to the sex composition of their study sample. Results - In 243 studies, 7 (3%) were women-only, 101 (41%) were mixed, with a disproportionate men-to-women ratio (P50 = 3.5; P75 = 12.4). A shift was observed from mixed and unspecified source populations to men-only final samples. Our results also suggest implicit generalization of results from men-only studies, a lack of tests of interaction and often unjustified sex-adjustment for mixed studies. Conclusions - The lower proportion of women in studies cannot be fully explained by their under-representation in the target populations, since there were large numbers of women among both potentially exposed workers and patients diagnosed with lung cancer.

International audience; Complex exposure situations are frequent at the workplace, but few studies have characterized multiple occupational carcinogenic exposures (MOCE) and their gendered differences across jobs’ characteristics. We assessed MOCE separately in male and female jobs and identified patterns of MOCE at job level. Participants (834 men and 183 women) were cancer patients recruited between March 2002 and December 2010 in the ongoing SCOP93 cohort study, Seine-Saint-Denis department, France. Job histories were collected through personal interviews, and carcinogenic exposures were assessed by a multidisciplinary expert committee using a list of 53 carcinogens. Proportion of MOCE (i.e. ≥2 carcinogens) was assessed for male and female jobs separately. Principal component analysis combined with hierarchical ascendant classification was used to identify patterns of MOCE. Among the 5202 male jobs and 885 female jobs, respectively 42 and 9% were multi-exposed. Blue-collar workers and jobs in the construction and industry sectors had the highest rates of MOCE, contrasting with jobs held in recent periods (≥1997) and by patients aged ≥45 years at job start. A gradient of MOCE was also observed according to occupational segregation for both men and women. Eight patterns of MOCE were identified among male jobs: widespread carcinogens, mixed silica dust, heavy metals/combustion products, organic compounds/radiation, metal working, solvents/heavy metals, wood dust/formaldehyde/pesticides, and fuel exhausts. Three patterns of MOCE were found among female jobs: biological/organic compounds, industrial working, and fuel exhausts. Some patterns of MOCE were job-specific, whereas other patterns were found across different occupations. These results suggest that patterns of MOCE partly differ between men and women. They stress the importance of gendering multiple exposure assessment studies and point out the inadequacy of occupational disease compensation systems based on a single factor and non-gendered approach of carcinogenesis, ignoring differences between men and women in complex occupational exposure situations.

To analyze the associations between marine n-3 polyunsaturated fatty acids (PUFAs) and blood pressure (BP), resting heart rate (HR), and heart rate variability (HRV) in a population highly exposed to methylmercury through the diet.Concentrations of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in erythrocytes membranes were measured in 180 French Polynesian adults (≥18 years) residing in Tubuai, which is a community with a traditional lifestyle, or Papeete, which has a modern lifestyle. HRV was measured using a 2-hour ambulatory electrocardiogram (Holter). Resting HR and BP were measured using standardized protocols and pulse pressure (PP) was calculated as systolic BP - diastolic BP. The associations between n-3 PUFAs and the dependent variables were studied using simple and multiple linear regressions.Increasing DHA concentration was associated with lower resting HR (β = -2.57, p = 0.005) and diastolic BP (β = -1.96, p = 0.05) and higher HRV in multivariable models. Specifically, DHA was associated with high frequency (HF; β = 0.19, p = 0.02) and the square root of the mean squared differences of successive R-R intervals (difference between two consecutive R waves; rMSSD; β = 0.08, p = 0.03), which are specific indices of the parasympathetic activity of the autonomic nervous system.DHA was associated with lower BP and resting HR and higher HRV among French Polynesians who are also exposed to high methylmercury levels.

Objectives. Because of their recent adoption of a Westernized lifestyle, an increased risk of developing hypertension (HTN) is suspected among Inuit populations. This study aimed to assess the exact prevalence of HTN in Nunavik Inuit and to examine its association with other major risk factors of cardiovascular disease. Study design. A cross-sectional population-based study. Methods. We analysed biological and anthropometric data and the medical history of 832 Inuit. Results. The overall prevalence of HTN (≥140/90 mmHg or the use of medication) was 19% with no gender difference. Obesity (body mass index [BMI] ≥30 kg/m2) was the highest prevalent cardiovascular risk factor (23%), and was significantly associated with HTN (OR for BMI

Background The Inuit are commonly portrayed to be somehow protected from cardiovascular diseases (CVDs) through their traditional lifestyle and diet. However, actual sociocultural transition and related major, modifiable risk factors have scarcely been quantified in the Inuit population. Such knowledge is extremely valuable in terms of public health intervention. Methods A total of 887 Inuit residents from Nunavik, Quebec, participated in a cohort study. The estimates presented were derived from anthropometric and biological measurements gathered at the time of recruitment and enhanced by information collected in the medical file of each participant. All estimates were corrected for a complex sampling strategy and bootstrapped to ensure the representativeness of the general Nunavik population. Results Overall, 19% of Inuit had a disease of the circulatory system according to the International Statistical Classification of Diseases and Related Health Problems, 10th revision . Among all disorders, peripheral circulatory system disease was the most prevalent (9%). Prevalences of ischemic heart disease and cerebrovascular disease were of similar magnitude (2.5%). No significant difference in disease prevalence was noted between sexes. The major modifiable CVD risk factors were smoking (84%), obesity (49%) (body mass index of greater than 30kg/m 2 ) and elevated blood pressure (130/85mmHg or greater) (18%). Prevalences were globally higher among women. Conclusion The current belief that the Inuit are protected from CVD is seriously questioned by the results of the present study. Considering the extremely high prevalence of CVD risk factors, a population-based intervention reinforced for women is urgently needed to reduce their risk.

As part of the rapid socio-cultural transition observed in Arctic populations, the Inuit diet is changing. We present original data derived from the baseline Inuit Health in Transition cohort study regarding biological levels ofn-3 fatty acids andtrans-fatty acids (TFA), lipids with opposite health effects found respectively in traditional marine diets and recently introduced low-quality imported foods. A total of 524 Inuit from the Disko Bay area (Greenland) and 888 Inuit from the fourteen communities of Northern Québec (Nunavik) participated in the study. We measured the fatty acid profile of erythrocyte (RBC) membrane phospholipids (PL) as a surrogate for individual intakes. Moreover, the contribution of store-bought foods to energy intakes was assessed through dietary questionnaires. Our results show that whilen-3 fatty acid levels were slightly lower in Nunavik (9·4 % of RBC membrane PL) than in Greenland (12·1 %), TFA levels were on average nearly thrice as high in Nunavik Inuit (1·20 %) as they were in Greenlanders (0·43 %). Moreover, younger Nunavik Inuit accumulated higher intakes of TFA and lower intakes ofn-3 fatty acids. Finally, the average proportion of energy derived from store-bought foods was high in both groups (77·5 % and 83·5 %), especially in youth. Our results call for action to rehabilitate and recover access to country foods and point to the importance for Nunavik and the entire circumpolar world to follow the example of Denmark and Greenland, which imposed a maximum content of 2 g/100 g fat on industrially producedtrans-fats in 2003.

The contamination of foods dedicated to human consumption varies over space and time. In exposure assessment, this is usually addressed through probabilistic modelling. The present work explores how the variability and uncertainty of exposures estimated at the population level are affected by: (a) the (non-)parametric nature of input contamination distributions; (b) the time-window used to sample contamination values within those distributions. Focusing on exposure of the French population to food mycotoxin ochratoxin A, we implement a range of second-order Monte-Carlo simulations that allow distinguishing variability of exposures from uncertainty of distributional parameters estimates. A simulation runs 10,000 iterations. Overall estimates of parameters are given by the median across iterations and 95%CI by 2.5th and 97.5th percentiles. Our results show that: (a) parametric (log-normal) input distributions may lead to over-estimation of variability and greater uncertainty as compared to non-parametric ones (P97.5 [95%CI] of 7.1 [6.6; 7.7] for Parametric-Occasion, 4.6 [4.3; 5.0] for Non-Parametric-Occasion), and that (b) the ‘Occasion’ time-window combines better estimate of variability and lower uncertainty when exposure modelling is applied to populations living in developed countries with complex agri-food systems (P97.5 [95%CI]: 7.3 [6.2; 8.9] for Non-Parametric-Week, 4.6 [4.3; 5.0] for Non-Parametric-Occasion). A deterministic approach is nevertheless preferred to probabilistic modelling every time input data quality is questionable.

Following our results, based on population studies conducted in Greenland and Northern Canada, that Nunavik Inuit were thrice as highly exposed to dietary trans -fat as were Greenlandic Inuit, and that the biological levels found in Nunavik were already associated with deleterious blood lipid profiles, we decided to engage in translational activities. Our goal was to support Inuit communities in the practical implementation of a reduction of the trans -fat content of food sold in Nunavik. We carried out a preliminary feasibility study in Kuujjuaq and participated in several meetings. This translational phase involved an Inuk leader, an Inuk student, a southern student, a southern nutritionist and a southern researcher in the framework of a public health project. In the present article, we recount the different phases of the process, from research implementation to results dissemination and institutional commitment to implement a primary prevention program of reduction in trans -fat exposure in Nunavik. This is the occasion to draw broader conclusions on the factors that could either act in favour of or, on the contrary, would likely compromise the implementation of primary prevention interventions dealing with food and nutrition in the Arctic. Finally, we share some reflections on future translational activities dealing with trans -fat as well as other junk food issues. The analytical framework we propose integrates a range of factors, from geo-climatic to socio-economic, ethnocultural, and even political, that we think should be examined while identifying and building preventive recommendations and strategies related to the Northern diet. Keywords: trans -fat; translational research; intervention; Inuit diet (Published: 20 July 2012) Citation: Int J Circumpolar Health 2012, 71 : 18833 - http://dx.doi.org/10.3402/ijch.v71i0.18833

Background Populations which diet is rich in seafood are highly exposed to contaminants such as mercury, which could affect cardiovascular risk factors Objective To assess the associations between mercury and blood pressure (BP), resting heart rate (HR) and HR variability (HRV) among French Polynesians Methods Data were collected among 180 adults (≥ 18 years) and 101 teenagers (12-17 years). HRV was measured using a two-hour ambulatory electrocardiogram (Holter) and BP was measured using a standardized protocol. The association between mercury and HRV and BP parameters was studied using analysis of variance (ANOVA) and analysis of covariance (ANCOVA) Results Among teenagers, the high frequency (HF) decreased between the 2nd and 3rd tertile (380 vs. 204 ms2, p = 0.03) and a similar pattern was observed for the square root of the mean squared differences of successive R-R intervals (rMSSD) (43 vs. 30 ms, p = 0.005) after adjusting for confounders. In addition, the ratio low/high frequency (LF/HF) increased between the 2nd and 3rd tertile (2.3 vs. 3.0, p = 0.04). Among adults, the standard deviation of R-R intervals (SDNN) tended to decrease between the 1st and 2nd tertile (84 vs. 75 ms, p = 0.069) after adjusting for confounders. Furthermore, diastolic BP tended to increase between the 2nd and 3rd tertile (86 vs. 91 mm Hg, p = 0.09). No significant difference was observed in resting HR or pulse pressure (PP) Conclusions Mercury was associated with decreased HRV among French Polynesian teenagers while no significant association was observed with resting HR, BP, or PP among teenagers or adults

To evaluate subclinical atherosclerosis in Nunavik Inuit and its correlation to traditional cardiovascular disease risk factor.The intima-media thickness (IMT) of 12 segments of the carotid arteries (IMT(12_seg)) free of plaque were assessed in randomly selected 40 years old and older Inuit from. Clinical assessment was performed which included fasting plasma glucose, fasting insulin, systemic blood pressure, body mass index, smoking, circulating blood lipids and oral glucose tolerance test. In addition, documented presence of ischemic heart disease (IHD), stroke, diabetes mellitus, hypertension and dyslipidemia were determined from medical files.The average age of the 287 participants was 51.2 ± 0.6 years (56.8% women). Mean IMT(12_seg) was 0.80 ± 0.17 mm (range: 0.55-1.47 mm). Compared with disease free Inuit, individuals with history of stroke showed greater carotid internal IMT (0.68 ± 0.01 mm vs. 0.96 ± 0.15 mm respectively; p0.005) but no difference was observed for IHD. Hypertensive and dyslipidemic Inuit had higher IMT(12_seg) compared to risk factor free individuals but no difference was observed in diabetics. None of the clinical assessments were associated with IMT(12_seg). In a multivariate backward elimination model, only age, gender, and medically documented history of hypertension were found to be predictors of IMT(12_seg) (adjusted r-square of 0.54; p0.0001).Compared with disease free Nunavik Inuit, subclinical signs of atherosclerosis determined by IMT was higher in individual diagnosed with stroke. Independent predictors of IMT(12_seg) in our group were age, gender and history of hypertension. No other traditional risk factors imparted IMT.

Higher dairy product intake has shown beneficial effects on body weight, blood pressure, type 2 diabetes, and cardiovascular disease (CVD) risk factors in Caucasian populations. This study evaluated dairy product intake and its association with body weight and CVD risk profile among a population undergoing a dietary transition in Canada, the Nunavik Inuit.Data were collected from August 27 to October 1, 2004, in the 14 villages of Nunavik on a Canadian research icebreaker (Canadian Coast Guard ship Amundsen). Dairy product intake and calcium intake were evaluated in 543 Inuit using a food frequency questionnaire. Physiological (lipid profile, fasting glucose, and insulin) and anthropometrical measurements were also obtained.The range of median dairy product intake extended from 120 g/d in the lowest tertile to 290 g/d in the highest tertile. The median of calcium intake was 524 mg/d. Participants in the highest tertile of dairy product consumption had higher body weight, fat-free mass, waist circumference, waist-to-hip ratio, and fasting glucose concentrations than participants in the lowest tertile (all p0.01). After adjustments for potential cofactors, no significant association was observed. A higher prevalence of Inuit participants with metabolic syndrome was observed in the higher tertile compared with the first tertile (10.3% vs 1.6%; p0.001).Higher dairy product intake in Nunavik Inuit is not related to protective effects on body weight and CVD. The consumption of dairy products in Nunavik Inuit is probably not sufficient to withdraw beneficial effects on body weight or CVD risk factors, as observed in North American populations.

Dietary exposure totrans-fatty acids (TFA) is likely to be high among Canadian Inuit; yet no data are available on the physiological effects of TFA in this population. The purpose of the present study was to assess the association between TFA and plasma lipid profiles in Inuit men and women living in Nunavik (Québec, Canada). In a cross-sectional, population-based survey, a total of 795 Nunavik Inuit eligible participants gave a blood sample. Exposure to TFA was assessed by their relative proportion in erythrocyte membrane. We performed multiple regression analysis using plasma lipids or their linear combinations as the dependent variables and TFA as the main predictor, adjusting for potential confounders. The associations varied markedly between the sexes and according to age. In men (n357, aged 36·3 (sd14·3) years, TFA 1·24 (sd0·54) %), TFA tended to be negatively associated with HDL-cholesterol (HDL-C), apoA1 and LDL particle size, and positively associated with non-HDL-C, LDL-cholesterol (LDL-C), apoB100, the apoB100:apoA1 ratio and the ratios of total cholesterol (TC), LDL-C and TAG to HDL-C. No such trends were observed in women (n438, aged 37·0 (sd14·1) years, TFA 1·16 (sd0·54) %), except for HDL-C and apoA1 in women aged 50 years and more. These results suggest that TFA could raise the risk of CHD in Inuit men at least through their physiological effects on plasma lipids. The differential associations reported in pre- and postmenopausal women need to be reproduced in other populations and in experimental studies addressing the influence of sex hormones in response to dietary fats.

The duration of food consumption survey may have a marked effect on estimates of usual nutrient intakes in individuals and groups. This arises from a high degree of within-person variability in food intakes, primarily on a day-to-day basis. Both the level of observation-populations versus individuals-and the desirable level of precision decide upon the 'fitness-for-purpose' of dietary survey duration. Though similar from a methodological standpoint, the question was rarely addressed in the case of non-nutrients. Our work aims at estimating the number of days of food records needed for the assessment of usual intakes of food chemicals as a function of research purpose. Focusing on the French population exposure to food mycotoxin ochratoxin A, we implement a range of well-established methods borrowed from the field of nutrient intakes assessment. Our results on OTA show that: (a) at the population level, as low as three days give satisfactory distributional estimates; yet, the implementation of variance reduction methods is of particular relevance when higher percentiles of exposure are at stake; (b) the estimation of individual usual intakes based on food records is behind practical possibilities, which calls for alternative options such as biomarkers of exposure. (c) 2005 Elsevier Ltd. All rights reserved.

Workshop on Ochratoxin A in Food - Recent Developments and SignificanceBaden, AUSTRIAJUN 29-JUL 01, 2005; One of the key questions when assessing the exposure to contaminants is the choice of the method and the impact of this choice on the result to be compared with the toxicological reference value. This problem is particularly significant in the case of ochratoxin A (OTA) for which the use of crude estimates can provide results close to the current provisional tolerable weekly intake (PTWI). This paper compares different exposure assessment models for OTA using the same data set for food consumption (i.e. French INCA survey 1999) for the same groups of the population (i.e. adults excluding under-reporters and children 3-14 years-old) but with various ways of handling the occurrence of OTA in food. The consumption and contamination data were combined through 11 different scenarios based on parametric and non-parametric modelling and on the use of analytical results obtained on raw commodities or on foodstuffs ready-to-eat. In order to assess exposure to OTA using data on consumption of processed and composite foods it was necessary to use recipe information in order to utilize available contamination data which only exists for raw materials. The impact of such an adjustment appears to be essential to avoid an overestimation of the exposure. The impact of the other assumptions and the choice of mathematical models influence the results less but should be considered and detailed carefully in future dietary exposure assessments.

Traditional cereal-based fermented foods are frequently used as complementary foods for infants and young children in Africa. This is the case for ben-saalga, a popular fermented gruel produced from pearl millet (Pennisetum glaucunt) in Burkina Faso. Detailed knowledge of traditional processing is a prerequisite for investigating ways to improve both the nutritional and sanitary qualities of the corresponding foodstuff. In this work, the traditional processing of pearl millet into ben-saalga was investigated in 24 production units, and fermentation kinetics were studied in pilot scale experiments. Processing steps include: washing (optional), soaking of the grains (first fermentation step), grinding and sieving of the wet flour, settling (second fermentation step), and cooking. The soaking step was mainly characterized by alcoholic fermentation whereas lactic acid fermentation occurred during the settling step. Fermentation kinetics during settling indicates a temporal variation of metabolic activity. Initially, both homofermentative and heterofermentative pathways were simultaneously active, and later only a homofermentative pathway was active. The paste produced at the end of settling had a low pH (4.0 +/- 0.4) and its microflora was dominated by lactic acid bacteria (LAB) with an amylolytic LAB/LAB ratio of 12%. Sucrose disappeared in the grains during soaking but was not detected in the soaking water, whereas glucose, fructose and maltose appeared transiently. Glucose and fructose were the main substrates observed for lactic acid fermentation during the settling step; however unbalanced fermentation led to the hypothesis that starch hydrolysis products may also serve as substrates for lactic acid formation. At the end of the processing, a 75% and 83% decrease was observed in phytate (IP6) and raffinose, respectively. The sour gruel ben-saalga resulting from cooking the sour paste had inadequate nutritional characteristics with respect to infants' and young children's requirements; it was characterized by fluid consistency (Bostwick flow: 137 mm/30 s) and low energy density (about 30 kcal/100 g of gruel). (c) 2005 Elsevier B.V. All rights reserved.

Background We aimed to estimate the seroprevalence of SARS-CoV-2 infection in France and to identify the populations most exposed during the first epidemic wave. Methods Random selection of individuals aged 15 years or over, from the national tax register (96% coverage). Socio-economic data, migration history, and living conditions were collected via self-computer-assisted-web or computer-assisted-telephone interviews. Home self-sampling was performed for a random subsample, to detect IgG antibodies against spike protein (Euroimmun), and neutralizing antibodies with in-house assays, in dried blood spots (DBS). Results The questionnaire was completed by 134,391 participants from May 2nd to June 2st, 2020, including 17,441 eligible for DBS 12,114 of whom were tested. ELISA-S seroprevalence was 4.5% [95% CI 3.9–5.0] overall, reaching up to 10% in the two most affected areas. High-density residences, larger household size, having reported a suspected COVID-19 case in the household, working in healthcare, being of intermediate age and non-daily tobacco smoking were independently associated with seropositivity, whereas living with children or adolescents did not remain associated after adjustment for household size. Adjustment for both residential density and household size accounted for much of the higher seroprevalence in immigrants born outside Europe, twice that in French natives in univariate analysis. Conclusion The EPICOV cohort is one of the largest national representative population-based seroprevalence surveys for COVID-19. It shows the major role of contextual living conditions in the initial spread of COVID-19 in France, during which the availability of masks and virological tests was limited. Supplementary Information The online version contains supplementary material available at 10.1186/s12879-021-06973-0.