• Clin Chem Lab Med · Aug 2020

    Lower nasopharyngeal viral load during the latest phase of COVID-19 pandemic in a Northern Italy University Hospital.

    • Nicola Clementi, Roberto Ferrarese, Marco Tonelli, Virginia Amato, Sara Racca, Massimo Locatelli, Giuseppe Lippi, Guido Silvestri, Massimo Clementi, and Nicasio Mancini.
    • Laboratory of Medical Microbiology and Virology, University "Vita-Salute" San Raffaele, Via Olgettina 58, 20132 Milan, Italy.
    • Clin Chem Lab Med. 2020 Aug 27; 58 (9): 1573-1577.

    ObjectivesA milder clinical course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been anecdotally reported over the latest phase of COVID-19 pandemic in Italy. Several factors may contribute to this observation, including the effect of lockdown, social distancing, lower humidity, lower air pollution, and potential changes in the intrinsic pathogenicity of the virus. In this regard, the clinical severity of COVID-19 could be attenuated by mutations in SARS-CoV-2 genome that decrease its virulence, as well as by lower virus inocula.MethodsIn this pilot study, we compared the reverse transcription polymerase chain reaction (RT-PCR) amplification profile of 100 nasopharyngeal swabs consecutively collected in April, during the peak of SARS-CoV-2 epidemic, to that of 100 swabs collected using the same procedure in May.ResultsThe mean Ct value of positive samples collected in May was significantly higher than that of samples collected in the previous period (ORF 1a/b gene: 31.85 ± 0.32 vs. 28.37 ± 0.5, p<0.001; E gene: 33.76 ± 0.38 vs. 29.79 ± 0.63, p<0.001), suggesting a lower viral load at the time of sampling. No significant differences were observed between male and females in the two periods, whilst higher viral loads were found in (i) patients over 60-years old, and (ii) patients that experienced severe COVID-19 during the early stages of the pandemic.ConclusionsThis pilot study prompts further investigation on the correlation between SARS-CoV-2 load and different clinical manifestation of COVID-19 during different phases of the pandemic. Laboratories should consider reporting quantitative viral load data in the molecular diagnosis of SARS-CoV-2 infection.

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