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Seroprevalence of SARS-CoV-2 and Infection Fatality Ratio, Orleans and Jefferson Parishes, Louisiana, USA, May 2020

Our take —

In a representative sample of 2,640 individuals from two parishes in Louisiana from May 9 to 15, 2020, 7.8% of individuals tested positive for SARS-CoV-2. There were disparities in seroprevalence by race, with Black participants experiencing a seroprevalence of 9.7% compared with 4.5% among white participants. The overall infection fatality ratio was 1.63%, and there were no significant differences by race. The infection fatality rate was higher than that observed in other settings, and should be interpreted carefully given the limited data; these data warrant further examination to better understand what may be leading to this high infection fatality ratio.

Study design

Case Series

Study population and setting

A representative community sample of 2,640 persons participated in a study designed to estimate the seroprevalence and the infection fatality ratio in Orleans and Jefferson parishes, Louisiana, USA. The study was conducted at 10 sites from May 9 to 15, 2020. The recruitment method ensured representation within the sample across more than 50 characteristics, including social determinants of health and demographics. Both real-time RT-PCR of nasopharyngeal swabs and qualitative IgG antibody blood tests were conducted. Participants were considered to be infected with SARS-CoV-2 if they tested positive on either est. Early-stage infections were excluded from the calculation of the infection fatality ratio.

Summary of Main Findings

Overall, 183 participants tested positive for SARS-CoV-2 (6.9% unadjusted, 7.8% census-weighted). Seroprevalence ranged from 4.5% among white participants to 9.8% among Black participants. There was significant geographic heterogeneity in seroprevalence. The overall infection fatality ratio (IFR) was 1.63%, and statistically similar for white, Black, and multiracial participants.

Study Strengths

The sample is reflective of the demographics and a range of characteristics of the target population (the populations of Orleans and Jefferson Parishes). Additionally, to ensure representativeness, the final estimates were weighted to account for any remaining differences between the sample and target population.


While this is a representative sample, the results of this study are primarily relevant for two parishes in Louisiana in May, 2020. In the current analysis, data presented were not disaggregated by symptom status or presented by testing results (e.g. PCR-positive only vs. PCR-positive and IgG-positive vs. IgG-positive only); the case fatality ratio was similarly not reported among those who had been symptomatic.

Value added

This study provides estimates of seroprevalence, and infection fatality ratio for two parishes in Louisiana.

This review was posted on: 21 August 2020