Laboratory analysis of two Delta SARS-CoV-2 variant outbreaks in the Port of Antwerp.

Introduction: The B.1.617.2 SARS-CoV-2 or Delta variant, first detected in India, has shown a rapid global spread due to its high transmissibility and now represents more than 99% of the currently circulating variants in Europe.

Methods and result: In May 2021, two ships that had recently arrived in the Port of Antwerp reported crew members with COVID-like symptoms. SARS-CoV-2 RNA was detected in nasopharyngeal swabs in 30 out of 45 skippers and the B.1.617.2 variant was identified via whole genome sequencing. Crew members were isolated or quarantined and repeatedly tested to assess the evolution of their SARS-CoV-2 viral load based on the cycle threshold (CT) values of the PCR reaction. Viral cultures were also taken at day 7 to detect viable virus and were compared with the subjects CT value at that moment. The shipper's clinical condition was closely observed using a digital home monitoring tool. Eleven crew members (37%) required hospitalization, with CT values of SARS-CoV-2 RNA being a good predictive factor for the hospitalization need. Furthermore, a clear correlation between CT values and positive viral culture was observed, hinting infectiousness even longer than 10 days after the intitial positive PCR test.

Conclusion: Our study of 2 Delta variant clusters shows that the initial CT value is a good predictor for hospitalization need and suggests that patients infected with this variant may remain infectious for a longer time period.