Narrow transmission bottlenecks and limited within-host viral diversity during a SARS-CoV-2 outbreak on a fishing boat.

The long-term evolution of viruses is ultimately due to viral mutants that arise within infected individuals and transmit to other individuals. Here, we use deep sequencing to investigate the transmission of viral genetic variation among individuals during a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak that infected the vast majority of crew members on a fishing boat. We deep-sequenced nasal swabs to characterize the within-host viral population of infected crew members, using experimental duplicates and strict computational filters to ensure accurate variant calling. We find that within-host viral diversity is low in infected crew members. The mutations that did fix in some crew members during the outbreak are not observed at detectable frequencies in any of the sampled crew members in which they are not fixed, suggesting that viral evolution involves occasional fixation of low-frequency mutations during transmission rather than persistent maintenance of within-host viral diversity. Overall, our results show that strong transmission bottlenecks dominate viral evolution even during a superspreading event with a very high attack rate.

Clinical Performance Characteristics of the Swift Normalase Amplicon Panel for Sensitive Recovery of Severe Acute Respiratory Syndrome Coronavirus 2 Genomes.

Amplicon-based sequencing methods are central in characterizing the diversity, transmission, and evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but need to be rigorously assessed for clinical utility. Herein, we validated the Swift Biosciences' SARS-CoV-2 Swift Normalase Amplicon Panels using remnant clinical specimens. High-quality genomes meeting our established library and sequence quality criteria were recovered from positive specimens, with 95% limit of detection of 40.08 SARS-CoV-2 copies/PCR. Breadth of genome recovery was evaluated across a range of CT values (11.3 to 36.7; median, 21.6). Of 428 positive samples, 413 (96.5%) generated genomes with <10% unknown bases, with a mean genome coverage of 13,545× ± SD 8382×. No genomes were recovered from PCR-negative specimens (n = 30) or from specimens positive for non-SARS-CoV-2 respiratory viruses (n = 20). Compared with whole-genome shotgun metagenomic sequencing (n = 14) or Sanger sequencing for the spike gene (n = 11), pairwise identity between consensus sequences was 100% in all cases, with highly concordant allele frequencies (R2 = 0.99) between Swift and shotgun libraries. When samples from different clades were mixed at varying ratios, expected variants were detected even in 1:99 mixtures. When deployed as a clinical test, 268 tests were performed in the first 23 weeks, with a median turnaround time of 11 days, ordered primarily for outbreak investigations and infection control.

Host-pathogen dynamics in longitudinal clinical specimens from patients with COVID-19.

Rapid dissemination of SARS-CoV-2 sequencing data to public repositories has enabled widespread study of viral genomes, but studies of longitudinal specimens from infected persons are relatively limited. Analysis of longitudinal specimens enables understanding of how host immune pressures drive viral evolution in vivo. Here we performed sequencing of 49 longitudinal SARS-CoV-2-positive samples from 20 patients in Washington State collected between March and September of 2020. Viral loads declined over time with an average increase in RT-QPCR cycle threshold of 0.87 per day. We found that there was negligible change in SARS-CoV-2 consensus sequences over time, but identified a number of nonsynonymous variants at low frequencies across the genome. We observed enrichment for a relatively small number of these variants, all of which are now seen in consensus genomes across the globe at low prevalence. In one patient, we saw rapid emergence of various low-level deletion variants at the N-terminal domain of the spike glycoprotein, some of which have previously been shown to be associated with reduced neutralization potency from sera. In a subset of samples that were sequenced using metagenomic methods, differential gene expression analysis showed a downregulation of cytoskeletal genes that was consistent with a loss of ciliated epithelium during infection and recovery. We also identified co-occurrence of bacterial species in samples from multiple hospitalized individuals. These results demonstrate that the intrahost genetic composition of SARS-CoV-2 is dynamic during the course of COVID-19, and highlight the need for continued surveillance and deep sequencing of minor variants.

Narrow transmission bottlenecks and limited within-host viral diversity during a SARS-CoV-2 outbreak on a fishing boat.

The long-term evolution of viruses is ultimately due to viral mutants that arise within infected individuals and transmit to other individuals. Here we use deep sequencing to investigate the transmission of viral genetic variation among individuals during a SARS-CoV-2 outbreak that infected the vast majority of crew members on a fishing boat. We deep-sequenced nasal swabs to characterize the within-host viral population of infected crew members, using experimental duplicates and strict computational filters to ensure accurate variant calling. We find that within-host viral diversity is low in infected crew members. The mutations that did fix in some crew members during the outbreak are not observed at detectable frequencies in any of the sampled crew members in which they are not fixed, suggesting viral evolution involves occasional fixation of low-frequency mutations during transmission rather than persistent maintenance of within-host viral diversity. Overall, our results show that strong transmission bottlenecks dominate viral evolution even during a superspreading event with a very high attack rate.

Cytomegalovirus Viremia Predicts Postdischarge Mortality in Kenyan HIV-Exposed Uninfected Children.

BACKGROUND: Cytomegalovirus (CMV) viremia is associated with mortality in severely ill immunocompetent adults and hospitalized children with HIV (CWH). We measured CMV viremia in HIV-exposed and -unexposed Kenyan children aged 1-59 months discharged from hospital and determined its relationship with postdischarge mortality. METHODS: CMV DNA levels were measured in plasma from 1024 children (97 of which were HIV exposed uninfected [HEU], and 15 CWH). Poisson and Cox proportional hazards regression models were used to identify correlates of CMV viremia ≥ 1000 IU/mL and estimate associations with 6-month mortality, respectively. RESULTS: CMV viremia was detected in 31% of children, with levels ≥ 1000 IU/mL in 5.8%. HIV infection, age < 2 years, breastfeeding, and midupper arm circumference < 12.5 cm were associated with CMV viremia ≥ 1000 IU/mL. Among HEU children, CMV ≥ 1000 IU/mL (hazard ratio [HR] = 32.0; 95% confidence interval [CI], 2.9-354.0; P = .005) and each 1-log increase in CMV viral load (HR = 5.04; 95% CI, 1.7-14.6; P = .003) were associated with increased risk of mortality. CMV viremia was not significantly associated with mortality in HIV-unexposed children. CONCLUSIONS: CMV levels at hospital postdischarge predict increased risk of 6-month mortality in Kenyan HEU children. CMV suppression may be a novel target to reduce mortality in HEU children. CLINICAL TRIAL REGISTRATION: NCT02414399.

Retrospective Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Symptomatic Patients Prior to Widespread Diagnostic Testing in Southern California.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused one of the worst pandemics in recent history. Few reports have revealed that SARS-CoV-2 was spreading in the United States as early as the end of January. In this study, we aimed to determine if SARS-CoV-2 had been circulating in the Los Angeles (LA) area at a time when access to diagnostic testing for coronavirus disease 2019 (COVID-19) was severely limited. METHODS: We used a pooling strategy to look for SARS-CoV-2 in remnant respiratory samples submitted for regular respiratory pathogen testing from symptomatic patients from November 2019 to early March 2020. We then performed sequencing on the positive samples. RESULTS: We detected SARS-CoV-2 in 7 specimens from 6 patients, dating back to mid-January. The earliest positive patient, with a sample collected on January 13, 2020 had no relevant travel history but did have a sibling with similar symptoms. Sequencing of these SARS-CoV-2 genomes revealed that the virus was introduced into the LA area from both domestic and international sources as early as January. CONCLUSIONS: We present strong evidence of community spread of SARS-CoV-2 in the LA area well before widespread diagnostic testing was being performed in early 2020. These genomic data demonstrate that SARS-CoV-2 was being introduced into Los Angeles County from both international and domestic sources in January 2020.

Treponema pallidum genome sequencing from six continents reveals variability in vaccine candidate genes and dominance of Nichols clade strains in Madagascar.

In spite of its immutable susceptibility to penicillin, Treponema pallidum (T. pallidum) subsp. pallidum continues to cause millions of cases of syphilis each year worldwide, resulting in significant morbidity and mortality and underscoring the urgency of developing an effective vaccine to curtail the spread of the infection. Several technical challenges, including absence of an in vitro culture system until very recently, have hampered efforts to catalog the diversity of strains collected worldwide. Here, we provide near-complete genomes from 196 T. pallidum strains-including 191 T. pallidum subsp. pallidum-sequenced directly from patient samples collected from 8 countries and 6 continents. Maximum likelihood phylogeny revealed that samples from most sites were predominantly SS14 clade. However, 99% (84/85) of the samples from Madagascar formed two of the five distinct Nichols subclades. Although recombination was uncommon in the evolution of modern circulating strains, we found multiple putative recombination events between T. pallidum subsp. pallidum and subsp. endemicum, shaping the genomes of several subclades. Temporal analysis dated the most recent common ancestor of Nichols and SS14 clades to 1717 (95% HPD: 1543-1869), in agreement with other recent studies. Rates of SNP accumulation varied significantly among subclades, particularly among different Nichols subclades, and was associated in the Nichols A subclade with a C394F substitution in TP0380, a ERCC3-like DNA repair helicase. Our data highlight the role played by variation in genes encoding putative surface-exposed outer membrane proteins in defining separate lineages, and provide a critical resource for the design of broadly protective syphilis vaccines targeting surface antigens.

Biotransformation of Daidzein, Genistein, and Naringenin by Streptomyces Species Isolated from High-Altitude Soil of Nepal.

Flavonoids have achieved widespread importance in pharmaceutical, food, and cosmetics industries. Furthermore, modification of these naturally occurring flavonoids to structurally diverse compounds through whole cell biotransformation with enhanced biological activities has numerous biotechnological applications. The present study investigated the biotransformation potential of Streptomyces species isolated from a high-altitude-soil sample towards selected flavonoid molecules. The biotransformed metabolites were confirmed by comparing the HPLC chromatogram with authentic compounds and LC-MS/MS analysis. Of these isolates, Streptomyces species G-18 (Accession number: MW663767.1) catalyzed isoflavone molecules daidzein and genistein to produce hydroxylated products at 24 h of reaction condition in a whole cell system. The hydroxylation of daidzein (4',7-dihydroxyisoflavone) was confirmed at 3'-position of the B ring to produce 3',4',7-trihydroxyisoflavone. In addition, Streptomyces species G-14 (Accession number: MW663770.1) and Streptomyces species S4L (Accession number: MW663769.1) also revealed the transformation of daidzein (4',7-dihydroxyisoflavone) to hydroxy daidzein at a distinct position than that of G-18 isolates, whereas thee Streptomyces species S4L reaction mixture with naringenin as a substrate also revealed the hydroxylated product. Our results demonstrated that microorganisms isolated from different ecological niches have broad application.

Specific allelic discrimination of N501Y and other SARS-CoV-2 mutations by ddPCR detects B.1.1.7 lineage in Washington State.

Real-time epidemiological tracking of variants of concern (VOCs) can help limit the spread of more contagious forms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), such as those containing the N501Y mutation. Typically, genetic sequencing is required to be able to track VOCs in real-time. However, sequencing can take time and may not be accessible in all laboratories. Genotyping by RT-ddPCR offers an alternative to rapidly detect VOCs through discrimination of specific alleles such as N501Y, which is associated with increased transmissibility and virulence. Here we describe the first cases of the B.1.1.7 lineage of SARS-CoV-2 detected in Washington State by using a combination of reverse-transcription polymerase chain reaction (RT-PCR), RT-ddPCR, and next-generation sequencing. We initially screened 1035 samples positive for SARS-CoV-2 by our CDC-based laboratory-developed assay using ThermoFisher's multiplex RT-PCR COVID-19 assay over four weeks from late December 2020 to early January 2021. S gene target failures (SGTF) were subsequently assayed by RT-ddPCR to confirm four mutations within the S gene associated with the B.1.1.7 lineage: a deletion at amino acid (AA) 69-70 (ACATGT), deletion at AA 145, (TTA), N501Y mutation (TAT), and S982A mutation (GCA). All four targets were detected in two specimens; follow-up sequencing revealed a total of 9 mutations in the S gene and phylogenetic clustering within the B.1.1.7 lineage. Next, we continued screening samples for SGTF detecting 23 additional B.1.1.7 variants by RT-ddPCR and confirmed by sequencing. As VOCs become increasingly prevalent, molecular diagnostic tools like RT-ddPCR can be utilized to quickly, accurately, and sensitively distinguish more contagious lineages of SARS-CoV-2.

Performance characteristics of the Abbott Alinity m SARS-CoV-2 assay.

Mass molecular diagnostic testing for the SARS-CoV-2 pandemic has drawn on laboratory developed tests, commercial assays, and fully-automated platforms to accommodate widespread demand. The Alinity m instrument by Abbott is capable of detecting several clinically relevant pathogens and has recently received FDA emergency use authorization for SARS-CoV-2 molecular testing. The Alinity m performs automatic sample preparation, RT-PCR assembly, amplification, detection, and result calculation in under two hours. Here, we validate the performance characteristics of the Alinity m SARS-CoV-2 assay in comparison with the Roche cobas 6800 and Hologic Panther Fusion platforms. Across 178 positive and 195 negative nasopharyngeal swab specimens (CT range 14.30-38.84), the Alinity m detected one additional positive specimen that was found to be negative on the Roche cobas 6800 (PPA 100%, NPA 99.5%). Across a separate set of 30 positive and 174 negative nasopharyngeal swab specimens (CT range 14.1-38.5), the Alinity m had 100% positive and negative agreement with the Hologic Panther Fusion. Using SeraCare SARS-CoV-2 RNA standards, the assay limit of detection was verified to be two-fold more sensitive than the parameters stated by the SARS-CoV-2 AMP kit package insert, at 50 virus copies/mL. Assay specificity was 100% over 20 specimens positive for other respiratory viruses and intraday precision was 100% concordant with <2% CV. These data illst u illustrate the Abbott Alinity m system's high concordance with reference assays and analyti high analytical for SARS-CoV-2 molecular detection.

Viral genomes reveal patterns of the SARS-CoV-2 outbreak in Washington State.

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has gravely affected societies around the world. Outbreaks in different parts of the globe have been shaped by repeated introductions of new viral lineages and subsequent local transmission of those lineages. Here, we sequenced 3940 SARS-CoV-2 viral genomes from Washington State (USA) to characterize how the spread of SARS-CoV-2 in Washington State in early 2020 was shaped by differences in timing of mitigation strategies across counties and by repeated introductions of viral lineages into the state. In addition, we show that the increase in frequency of a potentially more transmissible viral variant (614G) over time can potentially be explained by regional mobility differences and multiple introductions of 614G but not the other variant (614D) into the state. At an individual level, we observed evidence of higher viral loads in patients infected with the 614G variant. However, using clinical records data, we did not find any evidence that the 614G variant affects clinical severity or patient outcomes. Overall, this suggests that with regard to D614G, the behavior of individuals has been more important in shaping the course of the pandemic in Washington State than this variant of the virus.

SARS-CoV-2 ORF6 Disrupts Bidirectional Nucleocytoplasmic Transport through Interactions with Rae1 and Nup98.

RNA viruses that replicate in the cytoplasm often disrupt nucleocytoplasmic transport to preferentially translate their own transcripts and prevent host antiviral responses. The Sarbecovirus accessory protein ORF6 has previously been shown to be a major inhibitor of interferon production in both severe acute respiratory syndrome coronavirus (SARS-CoV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we show SARS-CoV-2-infected cells display an elevated level of nuclear mRNA accumulation compared to mock-infected cells. We demonstrate that ORF6 is responsible for this nuclear imprisonment of host mRNA, and using a cotransfected reporter assay, we show this nuclear retention of mRNA blocks expression of newly transcribed mRNAs. ORF6's nuclear entrapment of host mRNA is associated with its ability to copurify with the mRNA export factors, Rae1 and Nup98. These protein-protein interactions map to the C terminus of ORF6 and can be abolished by a single amino acid mutation in Met58. Overexpression of Rae1 restores reporter expression in the presence of SARS-CoV-2 ORF6. SARS-CoV ORF6 also interacts with Rae1 and Nup98. However, SARS-CoV-2 ORF6 more strongly copurifies with Rae1 and Nup98 and results in significantly reduced expression of reporter proteins compared to SARS-CoV ORF6, a potential mechanism for the delayed symptom onset and presymptomatic transmission uniquely associated with the SARS-CoV-2 pandemic. We also show that both SARS-CoV and SARS-CoV-2 ORF6 block nuclear import of a broad range of host proteins. Together, these data support a model in which ORF6 clogs the nuclear pore through its interactions with Rae1 and Nup98 to prevent both nuclear import and export, rendering host cells incapable of responding to SARS-CoV-2 infection.IMPORTANCE SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19), is an RNA virus with a large genome that encodes multiple accessory proteins. While these accessory proteins are not required for growth in vitro, they can contribute to the pathogenicity of the virus. We demonstrate that SARS-CoV-2-infected cells accumulate poly(A) mRNA in the nucleus, which is attributed to the accessory protein ORF6. Nuclear entrapment of mRNA and reduced expression of newly transcribed reporter proteins are associated with ORF6's interactions with the mRNA export proteins Rae1 and Nup98. SARS-CoV ORF6 also shows the same interactions with Rae1 and Nup98. However, SARS-CoV-2 ORF6 more strongly represses reporter expression and copurifies with Rae1 and Nup98 compared to SARS-CoV ORF6. Both SARS-CoV ORF6 and SARS-CoV-2 ORF6 block nuclear import of a wide range of host factors through interactions with Rae1 and Nup98. Together, our results suggest ORF6's disruption of nucleocytoplasmic transport prevents infected cells from responding to the invading virus.

Phylogenetic estimates of SARS-CoV-2 introductions into Washington State.

BACKGROUND: The first confirmed case of SARS-CoV-2 in North America was identified in Washington state on January 21, 2020. We aimed to quantify the number and temporal trends of out-of-state introductions of SARS-CoV-2 into Washington. METHODS: We conducted a phylogenetic analysis of 11,422 publicly available whole genome SARS-CoV-2 sequences from GISAID sampled between December 2019 and September 2020. We used maximum parsimony ancestral state reconstruction methods on time-calibrated phylogenies to enumerate introductions/exports, their likely geographic source (e.g. US, non-US, and between eastern and western Washington), and estimated date of introduction. To incorporate phylogenetic uncertainty into our estimates, we conducted 5,000 replicate analyses by generating 25 random time-stratified samples of non-Washington reference sequences, 20 random polytomy resolutions, and 10 random resolutions of the reconstructed ancestral state. RESULTS: We estimated a minimum 287 separate introductions (median, range 244-320) into Washington and 204 exported lineages (range 188-227) of SARS-CoV-2 out of Washington. Introductions began in mid-January and peaked on March 29, 2020. Lineages with the Spike D614G variant accounted for the majority (88%) of introductions. Overall, 61% (range 55-65%) of introductions into Washington likely originated from a source elsewhere within the US, while the remaining 39% (range 35-45%) likely originated from outside of the US. Intra-state transmission accounted for 65% and 28% of introductions into eastern and western Washington, respectively. CONCLUSIONS: There is phylogenetic evidence that the SARS-CoV-2 epidemic in Washington is continually seeded by a large number of introductions, and that there was significant inter- and intra-state transmission. Due to incomplete sampling our data underestimate the true number of introductions.

Phylogenetic estimates of SARS-CoV-2 introductions into Washington State.

BACKGROUND: The first confirmed case of SARS-CoV-2 in North America was identified in Washington state on January 21, 2020. We aimed to quantify the number and temporal trends of out-of-state introductions of SARS-CoV-2 into Washington. METHODS: We conducted a molecular epidemiologic analysis of 11,422 publicly available whole genome SARS-CoV-2 sequences from GISAID sampled between December 2019 and September 2020. We used maximum parsimony ancestral state reconstruction methods on time-calibrated phylogenies to enumerate introductions/exports, their likely geographic source (US, non-US, and between eastern and western Washington), and estimated date of introduction. To incorporate phylogenetic uncertainty into our estimates, we conducted 5,000 replicate analyses by generating 25 random time-stratified samples of non-Washington reference sequences, 20 random polytomy resolutions, and 10 random resolutions of the reconstructed ancestral state. FINDINGS: We estimated a minimum 287 introductions (range 244-320) into Washington and 204 exported lineages (range 188-227) of SARS-CoV-2 out of Washington. Introductions began in mid-January and peaked on March 29, 2020. Lineages with the Spike D614G variant accounted for the majority (88%) of introductions. Overall, 61% (range 55-65%) of introductions into Washington likely originated from a source elsewhere within the US, while the remaining 39% (range 35-45%) likely originated from outside of the US. Intra-state transmission accounted for 65% and 28% of introductions into eastern and western Washington, respectively. INTERPRETATION: The SARS-CoV-2 epidemic in Washington was continually seeded by a large number of introductions. Our findings highlight the importance of genomic surveillance to monitor for emerging variants due to high levels of inter- and intra-state transmission of SARS-CoV-2. FUNDING SOURCE: None.

Viral genomes reveal patterns of the SARS-CoV-2 outbreak in Washington State.

The rapid spread of SARS-CoV-2 has gravely impacted societies around the world. Outbreaks in different parts of the globe are shaped by repeated introductions of new lineages and subsequent local transmission of those lineages. Here, we sequenced 3940 SARS-CoV-2 viral genomes from Washington State to characterize how the spread of SARS-CoV-2 in Washington State (USA) was shaped by differences in timing of mitigation strategies across counties, as well as by repeated introductions of viral lineages into the state. Additionally, we show that the increase in frequency of a potentially more transmissible viral variant (614G) over time can potentially be explained by regional mobility differences and multiple introductions of 614G, but not the other variant (614D) into the state. At an individual level, we see evidence of higher viral loads in patients infected with the 614G variant. However, using clinical records data, we do not find any evidence that the 614G variant impacts clinical severity or patient outcomes. Overall, this suggests that at least to date, the behavior of individuals has been more important in shaping the course of the pandemic than changes in the virus.

In vivo antiviral host transcriptional response to SARS-CoV-2 by viral load, sex, and age.

Despite limited genomic diversity, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has shown a wide range of clinical manifestations in different patient populations. The mechanisms behind these host differences are still unclear. Here, we examined host response gene expression across infection status, viral load, age, and sex among shotgun RNA sequencing profiles of nasopharyngeal (NP) swabs from 430 individuals with PCR-confirmed SARS-CoV-2 and 54 negative controls. SARS-CoV-2 induced a strong antiviral response with up-regulation of antiviral factors such as OAS1-3 and IFIT1-3 and T helper type 1 (Th1) chemokines CXCL9/10/11, as well as a reduction in transcription of ribosomal proteins. SARS-CoV-2 culture in human airway epithelial (HAE) cultures replicated the in vivo antiviral host response 7 days post infection, with no induction of interferon-stimulated genes after 3 days. Patient-matched longitudinal specimens (mean elapsed time = 6.3 days) demonstrated reduction in interferon-induced transcription, recovery of transcription of ribosomal proteins, and initiation of wound healing and humoral immune responses. Expression of interferon-responsive genes, including ACE2, increased as a function of viral load, while transcripts for B cell-specific proteins and neutrophil chemokines were elevated in patients with lower viral load. Older individuals had reduced expression of the Th1 chemokines CXCL9/10/11 and their cognate receptor CXCR3, as well as CD8A and granzyme B, suggesting deficiencies in trafficking and/or function of cytotoxic T cells and natural killer (NK) cells. Relative to females, males had reduced B cell-specific and NK cell-specific transcripts and an increase in inhibitors of nuclear factor kappa-B (NF-κB) signaling, possibly inappropriately throttling antiviral responses. Collectively, our data demonstrate that host responses to SARS-CoV-2 are dependent on viral load and infection time course, with observed differences due to age and sex that may contribute to disease severity.

Cryptic transmission of SARS-CoV-2 in Washington state.

After its emergence in Wuhan, China, in late November or early December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus rapidly spread globally. Genome sequencing of SARS-CoV-2 allows the reconstruction of its transmission history, although this is contingent on sampling. We analyzed 453 SARS-CoV-2 genomes collected between 20 February and 15 March 2020 from infected patients in Washington state in the United States. We find that most SARS-CoV-2 infections sampled during this time derive from a single introduction in late January or early February 2020, which subsequently spread locally before active community surveillance was implemented.

In vivo antiviral host response to SARS-CoV-2 by viral load, sex, and age.

Despite limited genomic diversity, SARS-CoV-2 has shown a wide range of clinical manifestations in different patient populations. The mechanisms behind these host differences are still unclear. Here, we examined host response gene expression across infection status, viral load, age, and sex among shotgun RNA-sequencing profiles of nasopharyngeal swabs from 430 individuals with PCR-confirmed SARS-CoV-2 and 54 negative controls. SARS-CoV-2 induced a strong antiviral response with upregulation of antiviral factors such as OAS1-3 and IFIT1-3 , and Th1 chemokines CXCL9/10/11 , as well as a reduction in transcription of ribosomal proteins. SARS-CoV-2 culture in human airway epithelial cultures replicated the in vivo antiviral host response. Patient-matched longitudinal specimens (mean elapsed time = 6.3 days) demonstrated reduction in interferon-induced transcription, recovery of transcription of ribosomal proteins, and initiation of wound healing and humoral immune responses. Expression of interferon-responsive genes, including ACE2 , increased as a function of viral load, while transcripts for B cell-specific proteins and neutrophil chemokines were elevated in patients with lower viral load. Older individuals had reduced expression of Th1 chemokines CXCL9/10/11 and their cognate receptor, CXCR3 , as well as CD8A and granzyme B, suggesting deficiencies in trafficking and/or function of cytotoxic T cells and natural killer (NK) cells. Relative to females, males had reduced B and NK cell-specific transcripts and an increase in inhibitors of NF-κB signaling, possibly inappropriately throttling antiviral responses. Collectively, our data demonstrate that host responses to SARS-CoV-2 are dependent on viral load and infection time course, with observed differences due to age and sex that may contribute to disease severity.

Comparative Performance of SARS-CoV-2 Detection Assays using Seven Different Primer/Probe Sets and One Assay Kit.

More than 100,000 people worldwide are known to have been infected with SARS-CoV-2 beginning in December 2019. The virus has now spread to over 93 countries including the United States, with the largest cluster of US cases to date in the Seattle metropolitan area in Washington. Given the rapid increase in the number of local cases, the availability of accurate, high-throughput SARS-CoV-2 testing is vital to efforts to manage the current public health crisis. In the course of optimizing SARS-CoV-2 testing performed by the University of Washington Clinical Virology Lab (UW Virology Lab), we tested assays using seven different primer/probe sets and one assay kit. We found that the most sensitive assays were those the used the E-gene primer/probe set described by Corman et al. (Eurosurveillance 25(3), 2020, https://doi.org/10.2807/1560-7917.ES.2020.25.3.2000045) and the N2 set described by the CDC (Division of Viral Diseases, Centers for Disease Control and Prevention, 2020, https://www.cdc.gov/coronavirus/2019-ncov/downloads/rt-pcr-panel-primer-probes.pdf). All assays tested were found to be highly specific for SARS-CoV-2, with no cross-reactivity with other respiratory viruses observed in our analyses regardless of the primer/probe set or kit used. These results will provide invaluable information to other clinical laboratories who are actively developing SARS-CoV-2 testing protocols at a time when increased testing capacity is urgently needed worldwide.