Researchers who tested 68 respiratory specimens from 35 COVID-19 patients, of whom 32 had mild illness, found that live virus and evidence of viral replication were rarely detectable beyond eight days after symptom onset but that viral RNA was detectable for many weeks using RT-PCR, according to a news report from the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota.
The study, published in Emerging Infectious Diseases, involved isolating viable coronavirus in culture, detecting viral replication on subgenomic RNA (sgRNA), and identifying COVID-19 RNA on RT-PCR. The researchers isolated live virus from 16 specimens from 16 patients with high median viral loads, while specimens with low viral loads tended to culture negative.
In addition to virus culture, specimens with a moderate to high viral load were also assessed for sgRNA to detect viral replication. Twelve of the 33 specimens (36.4 percent) were positive on both tests, while 12 were negative on both. Seven of 33 (21.2 percent) were positive for sgRNA but negative on culture, and 2 (6.1 percent) were positive on culture but negative for sgRNA.
The researchers detected virus sgRNA in 18 of 22 specimens (81.8 percent) collected within eight days after symptom onset and in 1 of 11 (9.1 percent) collected 9 or more days after illness onset. A subset analysis of 42 specimens from patients who were not treated with antiviral drugs or whose specimens had been collected before they received the therapy produced similar results. RT-PCR detected coronavirus RNA in 10 of 35 patients (29 percent) for longer than 30 days.
