RESUMEN
Efficient wide-scale testing for SARS-CoV-2 is crucial for monitoring the incidence of the infection in the community. The gold standard for COVID-19 diagnosis is the molecular analysis of epithelial secretions from the upper respiratory system captured by nasopharyngeal (NP) swabs, which requires the intervention of trained personnel. Given the ease of collection, saliva has been proposed as a possible substitute to support testing at the population level. Here we describe the set-up of a laboratory, in an academic context, for the high-throughput screening of SARS-CoV-2 in the saliva from the community. A novel saliva collection device was designed to favour the safe and correct acquisition of the sample as well as the processivity of the downstream molecular analysis. To test the performance of the system,1025 paired saliva and nasopharyngeal samples were collected from individuals recruited at a public drive through testing facility and analysed in parallel. An overall moderate concordance (68%) between the two tests was found, with evidence that neither test can diagnose the infection in 100% of the cases. While the two tests performed equally well in symptomatic individuals, their discordance was mainly restricted to samples from convalescent individuals. The saliva test was at least as effective as NP swabs in asymptomatic individuals recruited for contact tracing. Our study, therefore, indicates that saliva testing can be a reliable tool for wide-scale COVID-19 screening in the community.
RESUMEN
To what extent infection with SARS-CoV-2 protects against subsequent reinfection or symptomatic reinfection is still unclear. In this cohort study, we analyzed surveillance records of COVID-19 cases identified between June 2020 and January 2021 in five Italian municipalities, where 77.7% of the entire population was screened for IgG antibodies in May 2020. We compared the risk of observing symptomatic infections in two mutually exclusive groups defined by the initial serological response. We estimated that the cumulative incidence of identified symptomatic infections in the IgG negative and positive cohorts was 2.67% (95%CI: 2.12% - 3.37%) and 0.14% (95%CI: 0.04% - 0.58%), respectively. The adjusted odd ratio of developing symptomatic infection in individuals previously exposed to SARS-CoV-2 was estimated at 0.054 (95%CI: 0.009 - 0.169). Quantifying protective immunity against COVID-19 disease elicited by natural infection with SARS-CoV-2 is essential to inform strategies for controlling the pandemic in the forthcoming months.
RESUMEN
BackgroundThere are conflicting results about the duration of antibodies induced by SARS-CoV-2, but several studies show a rapid decay in a few months after infection. To evaluate antibody decline, we re-evaluated the presence of anti-SARS-CoV-2 antibodies among individuals found seropositive in a first population survey conducted 4 months before. MethodsAll individuals above ten years of age resident in 5 municipalities of the Autonomous Province of Trento, northern Italy, who resulted IgG positive for anti-SARS-CoV-2 nucleocapsid (NC) antibodies in a serosurvey conducted on May 2020 were retested after 4 months. Anti-SARS-CoV-2 antibodies were detected using the Abbott SARS-CoV-2 IgG assay (Abbott Diagnostics, USA) detecting anti-NC antibodies. Samples that gave a negative result were re-tested using the same test plus Liaison SARS-CoV-2 IgG assay (DiaSorin, Italy) to assess anti-spike (S) S1/S2 IgG antibodies. Seroprevalence was calculated as the proportion of positive people on the total number of tested. A neutralizing assay was performed on a subgroup of formerly positives sera using fifty-percent tissue culture infective dose (TCID50) as endpoint dilution to produce a cytopathic effect in 50% of inoculated Vero E6 cells culture. In all the analyses a p value < 0.05 were considered statistically significant. Statistical analysis was performed by STATA version 16.1 (STATA Corp., College Station, Texas, USA). FindingsOverall, 1159 out of 1402 initially anti-NC seropositive participants were enrolled in the study. Of them, 480 (41.1%) became seronegative for anti-NC IgG antibodies. When 479 negative sera were tested for anti-S IgG, 373 samples (77.9%) resulted positives. A functional neutralization assay was performed on 106 sera showing high concordance with anti-S antibodies positivity. InterpretationA decline of anti-NC IgG values was recorded 4 months after the first evaluation. Worth of note, a high proportion of anti-NC seronegative individuals were positive for anti-spike IgG antibodies, which appear to persist longer and to better correlate with neutralization activity.