Prediction of Past SARS-CoV-2 Infections: A Prospective Cohort Study Among Swiss Schoolchildren

Abstract

Objective: To assess the predictive value of symptoms, sociodemographic characteristics, and SARS-CoV-2 exposure in household, school, and community setting for SARS-CoV-2 seropositivity in Swiss schoolchildren at two time points in 2020.Design: Serological testing of children in primary and secondary schools (aged 6–13 and 12–16 years, respectively) took place in June–July (T1) and October–November (T2) 2020, as part of the longitudinal, school-based study Ciao Corona in the canton of Zurich, Switzerland. Information on sociodemographic characteristics and clinical history was collected with questionnaires to parents; information on school-level SARS-CoV-2 infections was collected with questionnaires to school principals. Community-level cumulative incidence was obtained from official statistics. We used logistic regression to identify individual predictors of seropositivity and assessed the predictive performance of symptom- and exposure-based prediction models.Results: A total of 2,496 children (74 seropositive) at T1 and 2,152 children (109 seropositive) at T2 were included. Except for anosmia (odds ratio 15.4, 95% confidence interval [3.4–70.7]) and headache (2.0 [1.03–3.9]) at T2, none of the individual symptoms were significantly predictive of seropositivity at either time point. Of all the exposure variables, a reported SARS-CoV-2 case in the household was the strongest predictor for seropositivity at T1 (12.4 [5.8–26.7]) and T2 (10.8 [4.5–25.8]). At both time points, area under the receiver operating characteristic curve was greater for exposure-based (T1, 0.69; T2, 0.64) than symptom-based prediction models (T1, 0.59; T2, 0.57).Conclusions: In children, retrospective identification of past SARS-CoV-2 infections based on symptoms is imprecise. SARS-CoV-2 seropositivity is better predicted by factors of SARS-CoV-2 exposure, especially reported SARS-CoV-2 cases in the household. Predicting SARS-CoV-2 seropositivity in children in general is challenging, as few reliable predictors could be identified. For an accurate retrospective identification of SARS-CoV-2 infections in children, serological tests are likely indispensable.Trial registration number: NCT04448717.

Longitudinal change in SARS-CoV-2 seroprevalence in 3-to 16-year-old children: The Augsburg Plus study

“…In our study, six of a total of twelve confirmed seropositive children (50.0%) at baseline did not know that they had undergone SARS-CoV-2 infection. The finding of an underdiagnosis of SARS-CoV-2 infection in children is in accordance with two other investigations [ 10 , 11 ] although the extent of underdiagnosis varied between studies [ 12 – 14 ].…”

Feasibility of a surveillance programme based on gargle samples and pool testing to prevent SARS-CoV-2 outbreaks in schools

“…Diverse test strategies have been implemented in schools to detect SARS-CoV-2 since the first school closures in Spring, 2020. Participation rates were notably higher when gargle 37 or saliva 38 samples were employed than when oral 30 or nasopharyngeal 39 swabs were taken. Gargle samples were provided for pool testing by 63% of pupils in a study in Austria, before renewed school closures 37 and by 83% of pupils in STACADO.…”

“…The high participation rate, at 73%, may be explained by the non-invasiveness of the sample collection. By contrast, mouth/throat swabs, taken by study personnel for PCR-analysis, were offered in Zurich, with an uptake rate of 49% 30 . The high participation rate in providing saliva samples could also be because the target population had had contact with a positive case, however 38 .…”

“…A further consideration in the choice of test is the sensitivity and specificity. A comparison was performed between the number of positive rapid antigen tests and the number of positive tests through oral swab in the school surveillance study in Zurich 30 . False positive tests were reported for 0.6% of the children and 1.7% of the teachers tested.…”

“…Regular rapid antigen testing through self-administered anterior nasal swabs was introduced into German schools on a compulsory basis following school reopening after the recent lockdown. While immediate result availability is advantageous, collecting samples in schools carries a risk of viral transmission when masks are removed, and the specificity is lower than that of PCR tests 30 . Subsequent PCR-based confirmation of positive results is thus required.…”