Frequency of Symptoms and Asymptomatic SARS-CoV-2 Infection in Louisiana, USA

Background: While many surveillance studies of seroprevalence to SARS-CoV-2 rely on remnant blood samples obtained as medical waste, representative, prospective collection allows for analysis of a representative cross-section of symptomatic and asymptomatic presentation of infection in the community. Louisiana, and particularly New Orleans, were hard-hit in the early phase of the pandemic, and an ongoing outbreak was occurring in Baton Rouge throughout July. Methods: A representative, cross-sectional sample of subjects from two cities in Louisiana were sent to testing sites to complete a verbal consent, survey, nasopharyngeal swab, and blood draw. Swabs were tested for active viral shedding (PCR) and blood was tested for immunoglobulin G (IgG) specific to SARS-CoV-2. Findings: Anosmia was extremely predictive for a positive test (40·6% of those with anosmia tested positive, OR: 13·6; CI 10·1, 18·3) and 47·3% of the sample experienced no symptoms at all. A lower quantity of virus was noted during the contagious phase of infection in asymptomatic compared to symptomatic individuals. Symptom presentation clustered into three groups; low/no symptoms (0·4±0·9 symptoms on average), highly symptomatic (7·5±1·9) or moderately symptomatic (4·0±1·5). The probability of reporting symptoms changed with age; those under age 60 had a >50% probability of reporting symptoms while those 60 years and older had <50% probability of reporting symptoms in a non-linear relationship. Interpretation: Anosmia should be used as a screening criterion to differentiate from other illnesses, and, given the high ratio of asymptomatic individuals, mask mandates should be enforced. Asymptomatic individuals should be tested with cause. Funding: This study was funded by ReNOLA, Ochsner Health, the Baton Rouge Area Foundation, Louisiana COVID-19 Health Equity Task Force, and The Humana Foundation, the Blue Cross and Blue Shield of Louisiana Foundation, Healthy Blue, the Huey and Angelina Wilson Foundation, and the Irene W. and C.B. Pennington Foundation. Declaration of Interests: The authors have no other conflicts of interest to report. Ethics Approval Statement: This study was approved by the Ochsner Clinic Foundation Institutional Review Board #2020·163.