Viral cultures, cycle threshold values and viral load estimation for assessing SARS-CoV-2 infectiousness in haematopoietic stem cell and solid organ transplant patients: a systematic review

Oro-faecal transmission of SARS-CoV-2: A systematic review of studies employing viral culture from gastrointestinal and other potential sources

“…Viral culture has been reported infrequently in respiratory samples with cycle thresholds above 25 [34], and it is likely to assume similar results within faecal samples with high Ct values. Selecting samples with a RT-PCR cycle count of higher than 25 greatly reduces the likelihood of being able to culture SARS-CoV-2 [32, 39, 42]. In the studies in this review, in general, samples with relatively high RT-PCR cycle counts were subjected to viral culture testing.…”

Analysis of two sequential SARS-CoV-2 outbreaks on a haematology-oncology ward and the role of infection prevention

“…Therefore, our HCW policy was adapted in 2022 to a non-PCR follow-up policy, as the risk of transmission after 7 days of isolation was considered low [ 25 ]. Nowadays, for immunocompromised haematological and solid transplant patients, the infectious period is generally estimated to be 14–21 days [ [29] , [30] , [31] ], but as we also have experienced, it is sometimes much longer [ 32 ].…”

Judicious ending of isolation based on reverse transcription–polymerase chain reaction (RT-PCR) cycle threshold only for patients with coronavirus disease 2019 (COVID-19) requiring in-hospital therapy for longer than 20 days after symptom onset

“…The correlation between Ct values and the isolation of viable virus has been studied [ [15] , [16] , [17] ]. A Ct value > 30 could be used for ending isolation in clinically improving patients at least 21 days after symptom onset [ 18 ].…”

“…Additionally, the presence of culturable virus despite high Ct values might contribute to the high transmission rates of the Omicron variant [ 19 ]. Considering the difference in sensitivity among several RT-PCR and variant-specific differences in viral dynamics, we adopted Ct value ≥ 38 as the cutoff for ending isolation/precaution during the Omicron wave, although values lower than or comparable to 35 were generally used as the cutoff Ct in the test-to release protocol [ 8 , 10 , [15] , [16] , [17] ]. Isolation/precaution was continued after transfer to a non-COVID-19 ward in patients with Ct values 35–37.…”