Risk factors for SARS-CoV-2 infection: A test-negative case-control study with additional population controls (preprint)

ABSTRACT Objectives: To assess risk factors for SARS-CoV-2 infection by first comparing positive cases with negative controls as determined by polymerase chain reaction (PCR) testing and then comparing these two groups with an additional population control group. Design and setting: Test-negative design (TND), multicentre case-control study with additional population controls in South Eastern Norway. Participants: Adults who underwent SARS-CoV-2 PCR testing between February and December 2020. PCR-positive cases, PCR-negative controls, and additional age-matched population controls. Primary outcome measures: The associations between various risk factors based on self- reported questionnaire and SARS-CoV-2 infection comparing PCR positive cases and PCR- negative controls. Using subgroup analysis, the risk factors were then compared with a population control group. Univariate and multivariate regression analyses were performed. Results: In total, 400 SARS-CoV-2 PCR-positive cases, 719 PCR-negative controls, and 14,509 population controls were included. Male sex was associated with the risk of SARS- CoV-2 infection when PCR-positive cases were compared with PCR-negative controls (OR 1.9, 95% CI 1.4 to 2.6). Age, education level, comorbidities (asthma, diabetes, hypertension), an exercise were not associated with the risk of SARS-CoV-2 infection when PCR-positive cases were compared with PCR-negative controls. In the subgroup analysis comparing PCR- positive cases with age-matched population controls, asthma was associated with the risk of SARS-CoV-2 infection (OR 1.6, 95% CI 1.1 to 2.1). Daily or occasional smoking was negatively associated with the risk of SARS-CoV-2 infection in both analyses (OR 0.5, 95% CI 0.3 to 0.8 and OR 0.55, 95% CI 0.35, to 0.82, respectively). Conclusions: Male sex was a possible risk factor, whereas smoking was negatively associated with the risk of SARS-CoV-2 infection, when comparing PCR-positive cases and PCR- negative controls. Asthma was associated with the risk of SARS-CoV-2 infection when PCR- positive cases were compared with population controls.

SARS-CoV-2 antibody persistence after five and twelve months: A cohort study from South-Eastern Norway (preprint)

Objectives: To assess total antibody levels against Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS CoV-2) spike protein up to 12 months after Coronavirus Disease (COVID-19) infection in non-vaccinated individuals and the possible predictors of antibody persistence. Methods: This is a prospective multi-centre longitudinal cohort study. Participants The study included SARS-CoV-2 real-time polymerase chain reaction (RT-PCR) positive and negative participants in South-Eastern Norway from February to December 2020. Possible predictors of SARS-CoV-2 total antibody persistence was assessed. The SARS-CoV-2 total antibody levels against spike protein were measured three to five months after PCR in 391 PCR-positive and 703 PCR-negative participants; 212 PCR-positive participants were included in follow-up measurements at 10 to 12 months. The participants completed a questionnaire including information about symptoms, comorbidities, allergies, body mass index (BMI), and hospitalisation. Primary outcome The SARS-CoV-2 total antibody levels against spike protein three to five and 10 to 12 months after PCR positive tests. Results: SARS-CoV-2 total antibodies against spike protein were present in 366 (94%) non-vaccinated PCR-positive participants after three to five months, compared with nine (1%) PCR-negative participants. After 10 to 12 months, antibodies were present in 204 (96%) non-vaccinated PCR-positive participants. Of the PCR-positive participants, 369 (94%) were not hospitalised. The mean age of the PCR-positive participants was 48 years (SD 15, range 20-85) and 50% of them were male. BMI [≥] 25 kg/m 2 was positively associated with decreased antibody levels (OR 2.34, 95% CI 1.06 to 5.42). Participants with higher age and self-reported initial fever with chills or sweating were less likely to have decreased antibody levels (age: OR 0.97, 95% CI 0.94 to 0.99; fever: OR 0.33, 95% CI 0.13 to 0.75). Conclusion Our results indicate that the level of SARS-CoV-2 total antibodies against spike protein persists for the vast majority of non-vaccinated PCR-positive persons at least 10 to 12 months after mild COVID-19.