Higher viral loads in asymptomatic COVID-19 patients might be the invisible part of the iceberg

Infection. 2021 Feb;49(1):117-126. doi: 10.1007/s15010-020-01548-8. Epub 2020 Nov 24.


Purpose: SARS-CoV-2 virus dynamics in different hosts and different samples and their relationship with disease severity have not been clearly revealed. The aim of this study is to evaluate the viral loads of 6 different sample types (nasopharyngeal/oropharyngeal combined, oral cavity, saliva, rectal, urine, and blood) of patients with different ages and clinics, to reveal the relationship between disease course and SARS-CoV-2 viral load, and differences in viral loads of asymptomatic and symptomatic patients.

Methods: Nasopharyngeal/oropharyngeal, oral cavity, saliva, rectal, urine, and blood samples are collected from patients who were hospitalized with diagnosis of COVID-19 on admission. Laboratory analysis were carried out at Public Health Institute of Turkey Virology Reference and Research Laboratory.

Results: A total of 360 samples from 60 patients were obtained on admission. Fifteen (25%) of the patients were asymptomatic while 45 (75%) were symptomatic. A significant difference was found between mean ages of asymptomatic vs symptomatic patients (26.4 and 36.4, respectively, p = 0.0248). No PCR positivity were found in blood. Only one asymptomatic patient had positive PCR result for urine sample. Viral loads of asymptomatic patients were found to be significantly higher (p = 0.0141) when compared with symptomatic patients. Viral load had a significant negative trend with increasing age. A significant decrease in viral load was observed with increasing disease severity.

Conclusion: In conclusion, this study demonstrates that asymptomatic patients have higher SARSCoV-2 viral loads than symptomatic patients and unlike in the few study in the literature, a significant decrease in viral load of nasopharyngeal/oropharyngeal samples was observed with increasing disease severity. Factors associated with poor prognosis are found to be significantly correlated with low viral load.

Keywords: Anal swab; Asymptomatic; COVID-19; Oral cavity; Saliva; Severity; Urine; Viral load.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Asymptomatic Diseases*
  • COVID-19 / diagnosis*
  • COVID-19 / pathology
  • COVID-19 / virology*
  • COVID-19 Testing
  • Child
  • Child, Preschool
  • Cohort Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mouth / virology
  • Nasopharynx / virology
  • Oropharynx / virology
  • Prognosis
  • RNA, Viral / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • SARS-CoV-2 / genetics
  • SARS-CoV-2 / pathogenicity*
  • Saliva / virology
  • Severity of Illness Index
  • Viral Load*


  • RNA, Viral