Large-Scale Screening of Asymptomatic Persons for SARS-CoV-2 Variants of Concern and Gamma Takeover, Brazil

Abstract

We performed a large-scale severe acute respiratory syndrome coronavirus 2 screening campaign using 2 PCR-based approaches, coupled with variant genotyping, aiming to provide a safer environment for employees of Federal University in Curitiba, Brazil. We observed the rapid spread of the Gamma variant of concern, which replaced other variants in <3 months.

Keywords: Brazil; COVID-19; SARS-CoV-2; coronavirus disease; diagnosis; diagnostic techniques and procedures; environment and public health; respiratory infections; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

COVID-19 diagnoses, asymptomatic and variant frequency, and lethality, Paraná state, Brazil. A) COVID-19 diagnoses in Paraná and Federal University of Paraná (Curitiba, Brazil) mass testing program positivity rates by epidemiologic week. Blue bars summarize positive cases in Paraná by diagnosis day notified to state surveillance system through February 15, 2021. Red dots represent the fraction of positive cases in all samples from mass screening collection at Federal University of Paraná, smoothed by locally estimated scatterplot smoothing in the red line; pink shading indicates SE from locally estimated scatterplot smoothing fit. B) Overall lethality of COVID-19 in Paraná (purple line) and variant prevalence among asymptomatic and mildly symptomatic cases, by epidemiologic week. Numbers represent the absolute quantity of cases for each variant. Scales for the y-axes differ substantially to underscore patterns but do not permit direct comparisons. COVID-19, coronavirus disease; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 2

Violin plots of diagnostic C_t values for severe acute respiratory syndrome coronavirus 2–positive cases in Paraná state, Brazil, and detection performance for singleplex (A) and multiplex (B) genotyping methods. Violin plots are made by kernel-smoothed density plots from the actual data (represented by the dots). Horizonal lines within boxes indicate medians; upper and lower box limits indicate interquartile ranges. C_t, cycle threshold.