Relevance of cycle threshold values in mass screening by reverse-transcription-PCR during COVID-19 pandemic in Belgium: a decision-making support?

Abstract

Aim: The Belgium's strategy against COVID-19 was partly based on mass screening. Here, we reported the results observed in a Belgian mass screening center. Materials & methods: Between October 2020 and February 2021, 32,089 samples were collected analyzed with reverse-transcription PCR (Thermo Fisher Scientific kits and apparatus). Patients were categorized according to their contagiousness (extrapolated from the cycle threshold [Ct] values and the recommendation of Sciensano). Results: We observed association between Ct values and age, with higher Ct observed in extreme age groups (<6 years and >75 years). Conclusion: The analysis of the evolution of the contagiousness of these patients tested twice within a 7-day period showed the relevancy of the recommendation edited by Sciensano.

Keywords: COVID-19; epidemiology; mass screening; reverse-transcription PCR.

Figure 1.. Algorithm for the management of patient tested by reverse-transcription PCR according to the Sciensano’s recommendations.

Figure 2.. Cycle threshold value distribution among the studied population.

Figure 3.. Cycle threshold values according to age group.

Pairwise comparisons between groups were performed by using Kruskal–Wallis test. Significant differences were highlighted in bold (p < 0.05).

Figure 4.. Cycle threshold value distribution according to age.

Red represents the curve (95% CI in grey) of the polynomial model computed to assess relation between Ct values and individual age. Ct: Cycle threshold.

Figure 5.. Alluvial plot illustrating the dynamics of contagiousness of patients tested twice within 7 days and with at least one positive test during this 7-day period.