SARS-CoV-2 viral load distribution in different patient populations and age groups reveals that viral loads increase with age.

Abstract

Objectives: To describe the SARS-CoV-2 viral load distribution in different patient groups and age categories. Methods: All SARS-CoV-2 RT-PCR results from nasopharyngeal (NP) and oropharyngeal (OP) swabs (first PCR from unique patients only) that were collected between January 1 and December 1, 2020, in the Public Health Services regions Kennemerland and Hollands Noorden, province of Northern Holland, the Netherlands were included in this study. Swabs were derived from patients with respiratory symptoms who were presented at the general practitioner (GP) or hospital, hospital health care workers (HCWs) of four regional hospitals, nursing home residents and HCWs of multiple nursing homes, and in majority (>75%) from Public Health testing facilities of the two Public Health Services. SARS-CoV-2 PCR crossing point (Cp) values were used to estimate viral loads (higher Cp-values indicate lower viral loads). Results: In total, 278.470 unique patients were tested of whom 9.1% (n=25.365) were SARS-CoV-2 positive. As there were differences in viral load distribution between tested populations, further analyses focused on PCRs performed by public health services (n=211.933) where sampling and inclusion were uniform. These data present reveal a clear relation between age and SARS-CoV-2 viral load, with especially children aged<12 years showing lower viral loads than shown in adults (β: -0.03, 95CI% -0.03 to -0.02, p<0.001), independent of sex and/or symptom duration. Interestingly, the median Cp values between the oldest (>79 years) and youngest (<12 years) population differed by over 4 PCR cycles, suggesting approximately a 16 fold difference in viral load. In addition, the proportion of children aged < 12 years with a Cp-value >30 was significantly higher compared to the other patients (31.1% vs. 16.9%, p-value<0.001). Conclusion: We observed that in patients tested by public health services, SARS-CoV2 viral load increases significantly with age. Previous studies suggest that young children (<12 years) play a limited role in SARS-CoV-2 transmission. Currently, the relation between viral load and infectivity is not yet well understood, and further studies should elucidate whether the lower viral load in children is indeed related to their suggested limited role in SARS-CoV-2 transmission. Moreover, as antigen tests are less sensitive than PCR, these results suggest that SARS-CoV-2 antigen tests could have lower sensitivity in children than in adults.