Screening for Severe Acute Respiratory Syndrome Coronavirus 2 in Close Contacts of Individuals With Confirmed Infection: Performance and Operational Considerations

Abstract

Background Point-of-care and decentralized testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical to inform public health responses. Performance evaluations in priority use cases such as contact tracing can highlight trade-offs in test selection and testing strategies. Methods A prospective diagnostic accuracy study was conducted among close contacts of coronavirus disease 2019 (COVID-19) cases in Brazil. Two anterior nares swabs (ANS), a nasopharyngeal swab (NPS), and saliva were collected at all visits. Vaccination history and symptoms were assessed. Household contacts were followed longitudinally. Three rapid antigen tests and 1 molecular method were evaluated for usability and performance against reference reverse-transcription polymerase chain reaction (RT-PCR) on nasopharyngeal swab specimens. Results Fifty index cases and 214 contacts (64 household) were enrolled. Sixty-five contacts were RT-PCR positive during ≥1 visit. Vaccination did not influence viral load. Gamma variants were most prevalent; Delta variants emerged increasingly during implementation. The overall sensitivity of evaluated tests ranged from 33% to 76%. Performance was higher among symptomatic cases and those with cycle threshold (Ct) values <34 and lower among oligosymptomatic or asymptomatic cases. Assuming a 24-hour time to results for RT-PCR, the cumulative sensitivity of an anterior nares swab rapid antigen test was >70% and almost 90% after 4 days. Conclusions The near-immediate time to results for antigen tests significantly offsets lower analytical sensitivity in settings where RT-PCR results are delayed or unavailable.

Antigen concentration, viral load, and test performance for SARS-CoV-2 in multiple specimen types

“…This study investigated the relationship between antigen concentration and diagnostic test performance on different types of samples collected in a study conducted in Porto Velho, Brazil, in 2021 [ 8 ]. The study shows that antigen concentration is closely related to viral load when measured from the same specimen type.…”

“…The design of this clinical study has been described previously [ 8 ]. Briefly, between July and September 2021, a prospective diagnostic accuracy study was conducted among close contacts of 50 confirmed COVID-19-positive index cases in Porto Velho, Brazil.…”

“…Additionally, at each visit, two paired ANS, one NPS, and one saliva sample, from passive saliva that pools naturally in the mouth, were collected. The details of specimen collection have been previously published (supplementary materials in Zobrist et al, 2022 [ 8 ]). The STANDARD Q COVID-19 Ag Nasal Test was run on one ANS during the visit.…”

“…Specimens with cycle threshold (Ct) values <30 underwent genomic sequencing [ 8 ]. Genomic sequencing for this study was conducted using Illumina COVIDSeq® Test (Illumina Inc., United States), with some modifications [ 12 ], on Illumina’s MiSeq® or NextSeq 1000® sequencers.…”

“…In 2021, a prospective diagnostic accuracy study was conducted among close contacts of COVID-19-positive index cases in Porto Velho, Brazil [ 8 ]. This study evaluated the performance of four tests for SARS-CoV-2—including three rapid antigen tests (STANDARD Q COVID-19 Ag Nasal and Saliva tests [SD Biosensor, Republic of Korea] and the SARS-CoV-2 Ag Test [LumiraDx™ Limited, United Kingdom]), as well as one dual-plexed RT-PCR method that uses minimally processed saliva [ 9 , 10 ] (SalivaDirect™ protocol [Yale University, United States])—against a regulatory-approved RT-PCR assay run on NPS specimens.…”