Caution in interpretation of SARS-CoV-2 quantification based on RT-PCR cycle threshold value.

RT-PCR is the reference method for diagnosis of a Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) infection. During the setting up of 6 SARS-CoV-2 RT-PCR assays in our laboratory, comparative evaluations were systematically undertaken and allowed to evidence major discrepancies on cycle threshold RT-PCR results between techniques. These tendencies were confirmed in routine application when analyzing sequential samples from the same patients. Our aim was to examine the impact of the technique among factors influencing RT-PCR result, a far surrogate of 'viral load' in the heterogeneous environment of respiratory specimens.

Genetic diversity within human erythroviruses: identification of three genotypes.

B19 virus is a human virus belonging to the genus Erythrovirus: The genetic diversity among B19 virus isolates has been reported to be very low, with less than 2% nucleotide divergence in the whole genome sequence. We have previously reported the isolation of a human erythrovirus isolate, termed V9, whose sequence was markedly distinct (>11% nucleotide divergence) from that of B19 virus. To date, the V9 isolate remains the unique representative of a new variant in the genus Erythrovirus, and its taxonomic position is unclear. We report here the isolation of 11 V9-related viruses. A prospective study conducted in France between 1999 and 2001 indicates that V9-related viruses actually circulate at a significant frequency (11.4%) along with B19 viruses. Analysis of the nearly full-length genome sequence of one V9-related isolate (D91.1) indicates that the D91.1 sequence clusters together with but is notably distant from the V9 sequence (5.3% divergence) and is distantly related to B19 virus sequences (13.8 to 14.2% divergence). Additional phylogenetic analysis of partial sequences from the V9-related isolates combined with erythrovirus sequences available in GenBank indicates that the erythrovirus group is more diverse than thought previously and can be divided into three well-individualized genotypes, with B19 viruses corresponding to genotype 1 and V9-related viruses being distributed into genotypes 2 and 3.