High Amounts of SARS-CoV-2 Precede Sickness Among Asymptomatic Health Care Workers

J Infect Dis. 2021 Jul 2;224(1):14-20. doi: 10.1093/infdis/jiab099.


Background: Whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positivity among asymptomatic subjects reflects past or future disease may be difficult to ascertain.

Methods: We tested 9449 employees at Karolinska University Hospital, Stockholm, Sweden for SARS-CoV-2 RNA and antibodies, linked the results to sick leave records, and determined associations with past or future sick leave using multinomial logistic regression.

Results: Subjects with high amounts of SARS-CoV-2 virus, indicated by polymerase chain reaction (PCR) cycle threshold (Ct) value, had the highest risk for sick leave in the 2 weeks after testing (odds ratio [OR], 11.97; 95% confidence interval [CI], 6.29-22.80) whereas subjects with low amounts of virus had the highest risk for sick leave in the 3 weeks before testing (OR, 6.31; 95% CI, 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, .71-1.57).

Conclusions: High amounts of SARS-CoV-2 virus, as determined using PCR Ct values, was associated with development of sickness in the next few weeks. Results support the concept that PCR Ct may be informative when testing for SARS-CoV-2. Clinical Trials Registration. NCT04411576.

Keywords: SARS-CoV-2; antibodies; coronavirus; health care workers; sick leave.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Antibodies, Viral
  • Asymptomatic Diseases*
  • COVID-19 / diagnosis
  • COVID-19 / epidemiology*
  • COVID-19 / virology*
  • Disease Progression
  • Female
  • Health Personnel*
  • Hospitals, University
  • Humans
  • Male
  • Mass Screening
  • Middle Aged
  • Polymerase Chain Reaction
  • RNA, Viral
  • SARS-CoV-2* / genetics
  • Serologic Tests
  • Sick Leave / statistics & numerical data
  • Sweden / epidemiology
  • Young Adult


  • Antibodies, Viral
  • RNA, Viral

Associated data

  • ClinicalTrials.gov/NCT04411576