Retrospective analysis of seroprevalence in a cohort of university students of Rome (Italy) between September 2020 and July 2021.

Background: the reopening of Universities in a COVID-19 pandemic context represented a potential source of virus transmission among students.

Objectives: to measure the SARS-CoV-2 real circulation among university students attending the University of Rome 'Niccolò Cusano' by seroprevalence analysis.

Design: retrospective study based on a point-of-care (POC) SARS-CoV-2 rapid qualitative serological screening performed on asymptomatic students attending the University.

Setting And Participants: between September 2020 to July 2021 at Niccolò Cusano University, 9,588 SARS-CoV-2 lateral-flow rapid qualitative antibody assays were performed on a total of 2,423 asymptomatic students. Among them, 389 individuals with compulsory attendance were tested every 10 days for a minimum observational period of 7 months.

Main Outcome Measures: the prevalence of SARS-CoV-2 IgM/IgG antibodies was estimated at more levels. It was calculated: 1. the number of positive cases detected among the total number of students tested during the screening period; 2. the cumulative seroprevalence over the time, and the seroprevalence distribution over the months; 3. the duration of seropositivity after SARS-CoV-2 infection in the known previous infected students repeatedly tested.

Results: a total of 112 participants had a SARS-CoV-2 positive IgG and/or IgM antibodies test, 39 of them with a documented history of previous infection. In the remaining 73 cases, 24 were confirmed with an external quantitative serological analysis and identified as individuals with unknown previous SARS-CoV-2 exposure, 17 resulted false positive and 32 subjects were excluded. The total seroprevalence was 2.6% (95%CI 2.0%-3.3%) and among the 63 confirmed seropositive cases, 75% had detectable IgG antibodies, 3% had IgM antibodies, and 22% were positive for both IgM and IgG antibodies. In the 389 repeatedly-tested students, 36 students were positive to SARS-CoV-2 antibodies, 14 with unknown previous infection, and 22 with known previous infection. Among these, 50% retained immune memory up to 4 months post infection and 27% of cases retained seropositivity up to 7 months.

Conclusions: the data collected has been useful to measure a real epidemiological rate of the virus spread in a cohort of students in Italy as well as to obtain information on the antibodies seropositivity duration in individuals with previous infection.