New study suggests SARS-CoV-2 viral load is an indicator of mortality but shows that overall viral load may be decreasing over time
As the COVID-19 pandemic has unfolded and testing technology has been rapidly developed, a new area of COVID-19 testing is emerging as more relevant for laboratorians to consider. Research presented at the end of September 2020 has indicated that SARS-CoV-2 viral load is an evolving metric that indicates disease severity and mortality.
The viral load study was conducted by researchers from Wayne State University in Detroit. Presented at the European Society of Clinical Microbiology and Infectious Diseases, the study was performed by analyzing the viral load of SARS-CoV-2 from nasal swabs taken between April 4 and June 5.
Researchers classified viral load samples as low, intermediate, or high, based on relative viral loads. The findings from early April showed that only 25.5% of the samples indicated a low viral load, however, percentages shifted over time in favor of a low viral load. The number of samples with a low viral load by the end of the study decreased significantly with 70% of the samples having a low viral load.
Low Versus High Viral Load and COVID-19 Outcomes
In addition to the decrease in viral load over time, the study found a decrease in mortality that was correlated with the viral load. Researchers also found that patients with a higher viral load were statistically less likely to survive the course of their COVID-19 infection than patients who had intermediate or low viral loads.
The authors note that their study does not address potentially confounding variables when addressing the correlation between mortality and high viral load, but they write that their data “suggests an association between initial viral load and mortality”.
Learning from a Downward Trend in SARS-CoV-2 Viral Load
“Exact reasons for a decrease in initial viral load over time are unclear,” said El Zein, MD, the study’s lead author. “A downward trend in the initial viral load may reflect a reduction in the severity of the pandemic, and trends in the viral load values over time may represent a marker to assess the progress of the pandemic. Rapid implementation of social distancing measures, lockdown, and widespread use of face masks may have contributed to a decrease in the exposure to the virus.”
Weeks before this study was published, the COVID-19 STAT Intelligence Briefings Service spoke about viral load testing with Frederick (Fritz) Kiechle, MD, PhD, Medical Director at Boca Biolistics in Pompano Beach, Florida, and a well-recognized expert within the clinical laboratory community. At the time, Kiechle suggested that viral load testing should be considered in clinical laboratories conducting SARS-CoV-2 PCR testing.
Should Clinical Laboratory Testing for Viral Load Become Routine?
“In my mind viral load is something we’ve sort of overlooked, and companies aren’t pushing,” Kiechle told STAT COVID-19. “It may be one of those tests that turns into a routine addition to the profile that we’re doing. You can actually do it with the qualitative test that we do, all you have to do is get some mathematics involved and do some additional measurements to figure out a viral load. It’s not impossible; it’s just that it’s additional steps, and not many do it.”
As new evidence emerges about viral load as an indicator of mortality—that viral load may decrease or fluctuate over time—Kiechle’s insights into the importance of this metric are timely and relevant. Clinical laboratories that do not test viral load should consider calculating viral load when performing COVID-19 PCR testing.
Evaluating viral load during COVID-19 testing will not only build upon the data from the Wayne State University study, but it may offer valuable prognostic information for patients and increase understanding of the SARS-CoV-2 coronavirus and COVID-19 disease.
—By Caleb Williams, Editor, COVID-19 STAT