ABSTRACT
Background. Congregate military populations remain at risk of SARS-CoV-2 outbreaks and the optimal surveillance approach in such settings remains unclear. We enrolled midshipmen at the United States Naval Academy (USNA) in a setting of frequent PCR screening use of prevention strategies. Methods. Dried blood spots (DBS) and saliva were collected in August 2020, December 2020, February 2021 (saliva only) and April/May 2021 to measure anti-SARS-CoV-2 spike (S) and nucleoprotein (NP) IgG. COVID-19 vaccine history and records of SARS-CoV-2 PCR tests and routine asymptomatic screening assays were obtained from the USNA Brigade Medical Clinic. Attack rates were compared with cumulative frequencies of infections. Concordance of saliva and DBS anti-NP and anti-S IgG positivity was determined using Cohen's kappa coefficient. Results. The study enrolled 181 midshipmen. COVID-19 vaccinations were administered in March/April 2021. Samples were collected for 101 participants in August, 73 in December, 57 in February (saliva only), and 63 in April/May. In August, 17 (17%) participants showed evidence of SARS-CoV-2 infection based on anti-S IgG values from DBS and/or saliva. By December 2020, anti-S seroconversion was observed for 5 more based on DBS and/or saliva. By May 2021, 100% of participants were anti-S IgG seropositive after vaccination based on DBS and/or saliva;48% of participants had seroconverted to anti-NP IgG. Among participants with both DBS and saliva samples, a coefficient of 0.64 showed substantial agreement between anti-S IgG results in August and perfect agreement in December (Table 1). DBS and saliva results for anti-NP IgG were in perfect agreement through December and in substantial agreement in May (0.68, Table 2). Prior to vaccination in March/April 2021, 4/48 of participants had at least one documented SARS-CoV-2 PCR positive result (Table 3). Cumulative PCR test positivity concordance with DBS seroconversion was 37.5% and 60% for anti-S IgG and anti-NP IgG, respectively. Conclusion. There was a substantive SARS-CoV-2 attack rate before vaccination;all vaccinees mounted an anti-S IgG response in blood. We note high agreement between DBS and saliva for IgG measurement. Serology-based surveillance identified substantially more SARS-CoV-2 infections than PCR screening.
ABSTRACT
Background. University students, including those at military service academies, are at increased risk of acute respiratory infection (ARI), including SAR-CoV-2, due to crowded living conditions, frequent social interaction and other factors that facilitate pathogen transmission. Unlike many universities, the United States Naval Academy (USNA) continued in-person instruction in Fall 2020 in the midst of the COVID-19 pandemic. The Observational Seroepidemiologic Study of COVID-19 at the United States Naval Academy (TOSCANA,) a longitudinal cohort characterizes the burden and risk factors of SARS-CoV-2 in USNA midshipmen. Methods. Midshipmen were enrolled August- October 2020. Participants were queried about their ARI risk factors, COVID-19 history, and recent receipt of medical care for any ARI at enrollment, in December 2020 and again in May 2021. Subjects were also asked to provide blood and saliva samples to assess their SARS-CoV-2 serostatus at the same three timepoints. A saliva sample was collected by a subset of subjects in February 2021. Presence of anti-SARS-CoV-2 serum IgG in dried blood spots and saliva was measured by multiplex magnetic microparticle-based immunoassays. Results. 181 midshipmen consented to the study and completed the baseline survey (Table 1). 17 (17.5%) of the 97 subjects who submitted baseline blood sample were SARS-CoV-2 seropositive. Only 4 (24%) positive individuals reported having been tested for or diagnosed with COVID-19 prior to arrival at USNA. 121 participants completed the midyear survey, of whom 61 (50%) submitted a blood sample. 16 (26%) of the midyear specimens were SARS-CoV-2 positive. Of these, 3 were new infections. 73 subjects completed the May survey, and 63 (100%) of the submitted blood samples were positive. 83 subjects provided baseline saliva samples, and ~55 submitted saliva at each successive time point. 1 (5%) was positive at enrollment, 9 (17%) were positive at midyear and 47 (96%) were positive in May. Conclusion. SAR-CoV-2 prevalence in a sample of USNA midshipmen was < 20% at enrollment. A small proportion of subjects seroconverted between the September and December visits. SARS-CoV-2 positivity rose in May, following a COVID-19 outbreak in February and COVID-19 vaccination efforts in March at USNA.
ABSTRACT
Background: Sustained molecular detection of SARS-CoV-2 RNA in the upper respiratory tract (URT) is common and confounds infection control efforts in the community. The mean duration of viral RNA detection is ∼17 days, and ∼14% of people with mild or no symptoms have detectable viral RNA for > 4 weeks. We sought to identify host and immune determinants of prolonged SARS-CoV-2 RNA detection in an intensively-sampled prospective observational cohort of outpatients with mild COVID-19 who had concomitant URT virus and mucosal IgG sampling. Methods: 95 participants ≥ 30 years old with known symptom onset date and at least two positive SARS-CoV-2 qRT-PCR results were enrolled. Participants self-collected mid-nasal, oropharyngeal, and oral crevicular fluid (OCF) samples 4-5 times within 3 weeks. 1-3 months after symptom onset, height and weight were measured and nasopharyngeal, salivary, OCF, and blood samples were collected. SARS-CoV-2 qRT-PCR was performed on samples, and positive samples were tested for propagation in virus culture. A multiplex mucosal IgG immunoassay with multiple SARS-CoV-2 antigens was performed on OCF. Plasma titers of neutralizing antibodies, SARS-CoV-2 spike (S) antibodies, and S-receptor binding domain (RBD) antibodies were obtained by microneutralization assay and indirect ELISA. Time to qRT-PCR clearance wasmeasured from symptom onset until the midpoint between the last positive qRT-PCR test and the next negative test. Associations were estimated using a Cox proportional hazard model. Hazards of viral RNA clearance were compared for different age, sex, race/ethnicity, and body mass index (BMI) groups and whether fever was one of the first three symptoms, adjusting for comorbidities and immunocompromised status. Results: See Table for participant characteristics. Of 56 participants with observed viral RNA clearance, mean time to clearance was 33.5 days. The hazard ratio for obesity vs overweight/normal weight was 0.37 (95% CI 0.18-0.78, p=0.009). Elevated mucosal SARS-CoV-2-specific IgG did not associate with faster viral RNA clearance. The maximum time from symptom onset to virus culture. positive sample was 12 days, which is just after the mean time of first positive mucosal SARS-CoV-2-specific IgG detection. Conclusion: Obesity is associated with prolonged SARS-CoV-2 RNA detection in outpatients. Mucosal SARS-CoV-2 IgG is not associated with faster clearance of viral RNA from the URT, suggesting that viral clearance is mediated by select host immune responses.