SARS-CoV-2 immunoassays in a predominantly vaccinated population: Performances and qualitative agreements obtained with two analytical approaches and four immunoassays.

BACKGROUND AND OBJECTIVES: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serosurveys are typically analysed by applying a fixed threshold for seropositivity ('conventional approach'). However, this approach underestimates the seroprevalence of anti-nucleocapsid (N) in vaccinated individuals-who often exhibit a difficult-to-detect anti-N response. This limitation is compounded by delays between the onset of infection and sample collection. To address this issue, we compared the performance of four immunoassays using a new analytical approach ('ratio-based approach'), which determines seropositivity based on an increase in anti-N levels. MATERIALS AND METHODS: Two groups of plasma donors and four immunoassays (Elecsys total anti-N, VITROS total anti-N, Architect anti-N Immunoglobulin G (IgG) and in-house total anti-N) were evaluated. First-group donors (N = 145) had one positive SARS-CoV-2 polymerase chain reaction (PCR) test result and had made two plasma donations, including one before and one after the PCR test (median = 27 days post-PCR). Second-group donors (N = 100) had made two plasma donations early in the Omicron wave. RESULTS: Among first-group donors (97.9% vaccinated), sensitivity estimates ranged from 60.0% to 89.0% with the conventional approach, compared with 94.5% to 98.6% with the ratio-based approach. Among second-group donors, Fleiss's κ ranged from 0.56 to 0.83 with the conventional approach, compared with 0.90 to 1.00 with the ratio-based approach. CONCLUSION: With the conventional approach, the sensitivity of four immunoassays-measured in a predominantly vaccinated population based on samples collected ~1 month after a positive test result-fell below regulatory agencies requirement of ≥95%. The ratio-based approach significantly improved the sensitivities and qualitative agreement among immunoassays, to the point where all would meet this requirement.

Viral Respiratory Infections in Hospitalized Children With Symptomatic Caregivers.

OBJECTIVES: The burden of healthcare-associated viral respiratory infections (HAVRIs) among children is significant. While healthcare workers are often the focus for infection prevention strategies, little is known about the impact of sick caregivers and hospital visitors on the incidence of pediatric HAVRIs. The objective of this descriptive study was to determine the proportion of pediatric HAVRIs following contact with a sick caregiver or visitor. METHODS: A retrospective chart review was performed of all HAVRIs that occurred between December 2017 and July 2019 in a pediatric tertiary care center. A HAVRI was defined as a laboratory-confirmed respiratory viral illness occurring more than 72 hours after admission. RESULTS: Forty-four HAVRIs occurred in 37 patients during the study, predominantly among patients aged <24 months (n = 32, 72.7%) and with comorbidities (n = 42, 95.5%). For 9 HAVRIs (20.5%), contact with a sick caregiver (n = 8, 18.2%) or visitor (n = 2, 4.5%) in the 7 days before diagnosis was documented. In the 72 hours before HAVRI onset, 18 of the 44 patients (40.9%) were in a single-bed room and 6 of them (33.3%) were under additional precautions. Twelve patients (27.3%) had new or increased oxygen requirements and 4 (9.1%) were transferred to the ICU. There were no associated deaths. CONCLUSIONS: Contact with a sick caregiver or visitor is a potential risk factor for acquiring a HAVRI. Our study reinforces the importance of engaging family caregivers in infection prevention and control strategies in pediatric care settings.