Since the emergence of SARS-CoV-2 pandemic, clinical laboratories worldwide are overwhelmed with SARS-CoV-2 testing using the current gold standard: real-time reverse-transcription polymerase chain reaction (RT-PCR) assays. The large numbers of suspected cases led to shortages in numerous reagents such as specimen transport and RNA extraction buffers. We try to provide some answers on how strongly preanalytical issues affect RT-PCR results by reviewing the utility of different transport buffer media and virus inactivation procedures and comparing the literature data with our own recent findings. We show that various viral inactivation procedures and transport buffers are available and are less of a bottleneck for PCR-based methods. However, efficient alternative lysis buffers remain more difficult to find, and several fast RT-PCR assays are not compatible with guanidine-containing media, making this aspect more of a challenge in the current crisis. Furthermore, the availability of different SARS-CoV-2-specific RT-PCR kits with different sensitivities makes the definition of a general cutoff level for the cycle threshold (Ct) value challenging. Only a few studies have considered how Ct values relate to viral infectivity and how preanalytical issues might affect viral infectivity and RNA detection. We review the current data on the correlation between Ct values and viral infectivity. The presence of the SARS-CoV-2 viral genome in its own is not sufficient proof of infectivity and caution is needed in evaluation of the infectivity of samples. The correlation between Ct values and viral infectivity revealed an RT-PCR cutoff value of 34 cycles for SARS-CoV-2 infectivity using a laboratory-developed RT-PCR assay targeting the RdRp gene. While ideally each clinical laboratory should perform its own correlation, we believe this perspective article could be a reference point for others, in particular medical doctors and researchers interested in COVID-19 diagnostics, and a first step toward harmonization.

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The ongoing outbreak of monkeypox virus (MPXV) is the largest one in historically non‐endemic countries. Early reports described atypical epidemiological and clinical presentations. We investigated MPXV DNA detection in oropharyngeal samples (OPS), and compared the viral load to that in lesion samples at diagnosis in patients infected with MPXV. We retrospectively included patients suspected to have monkeypox in Northern France, who underwent a MPXV PCR in the Virology Laboratory, University Hospital of Lille, from May 23 to August 18, 2022. Overall, a total of 228 patients (376 samples) were included. A positive result in at least one sample was found in 138 patients (60.5%). We compared PCR results between OPS and lesion samples (i.e., cutaneous or anal/rectal samples) in patients with both samples. A positive result in OPS was observed in 54 out of 60 patients (90%). The viral load in OPS (median Ct value = 29.5; interquartile range [IQR] = 24.7−34) was significantly lower than that in lesion samples (median Ct value = 17.8; IQR = 16.3 and 19.7) (p < 0.0001). This report shows that pharyngeal sampling does not bring additional information for the initial diagnosis in patients presenting with typical lesions.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused an ongoing pandemic. Reverse transcription polymerase chain reaction (RT-PCR) is the gold standard for the detection of SARS-CoV-2 and has been applied to different specimen types. Understanding the virus load and virus detection frequency in different specimen types is important to improve diagnosis and estimate the duration of potential infectivity. We conducted a retrospective single-center cohort study on hospitalized and outpatients with SARS-CoV-2 infection. We analyzed the frequency of virus detection, virus load, and duration of the virus excretion in upper and lower respiratory specimens as well as stool and plasma. We found that the frequency of SARS-CoV-2 detection, the virus load, and duration of virus excretion was higher in lower respiratory tract (LRT) than in upper respiratory tract (URT) specimens. The duration of virus excretion was longer in patients requiring intensive care unit (ICU) admission. In conclusion, LRT specimens are the most appropriate specimen type for the detection and follow-up of SARS-CoV-2 infection. Duration of virus excretion is longer in severe cases of SARS-CoV-2 infection.