High amounts of SARS-CoV-2 precede sickness among asymptomatic healthcare workers

Dillner, Joakim; Elfström, K Miriam; Blomqvist, Jonas; Engstrand, Lars; Uhlén, Mathias; Eklund, Carina; Boulund, Fredrik; Lagheden, Camilla; Hamsten, Marica; Nordqvist-Kleppe, Sara; Seifert, Maike; Hellström, Cecilia; Olofsson, Jennie; Andersson, Eni; Falk, August Jernbom; Bergström, Sofia; Hultin, Emilie; Pin, Elisa; Pimenoff, Ville N; Hassan, Sadaf; Månberg, Anna; Nilsson, Peter; Hedhammar, My; Hober, Sophia; Mattsson, Johan; Mühr, Laila Sara Arroyo; Lundgren, Kalle Conneryd

BACKGROUND: Whether SARS-CoV-2 positivity among symptomatic subjects reflects past or future disease may be difficult to ascertain. METHODS: We tested a cohort of 9449 employees at work at the Karolinska University Hospital, Stockholm, Sweden for SARS-CoV-2 RNA and antibodies, linked the testing results to sick leave records and determined associations with past or future sick leave using multinomial logistic regression. ClinicalTrials.gov NCT04411576. RESULTS: Subjects with high amounts of SARS-CoV-2 virus, as indicated by the Cycle threshold (Ct) value in the PCR, had the highest risk for sick leave in the two weeks after testing (OR 11.97 (CI 95% 6.29-22.80)) whereas subjects with low amounts of virus had the highest risk for sick leave in the past three weeks before testing (OR 6.31 (4.38-9.08)). Only 2.5% of employees were SARS-CoV-2 positive while 10.5% were positive by serology and 1.2% were positive in both tests. Serology-positive subjects were not at excess risk for future sick leave (OR 1.06 (95% CI, 0.71-1.57)). CONCLUSIONS: High amounts of SARS-CoV-2 virus, as determined using PCR Ct values, associates with development of sickness in the next few weeks. The results support the concept that PCR Ct may be informative when testing for SARS-CoV-2 is performed.