The levels of the virus that causes COVID-19 has been declining in U.S. patients over time, which could account for the lower number of ICU admissions and overall death rate compared to when the virus first arrived, researchers claim.
The study, conducted by Wayne State University researchers and presented at the European Society of Clinical Microbiology and Infectious Diseases, relied on nasal swabs taken from hospitalized patients in Detroit between April 4 and June 5. They then assessed all samples that had tested positive for SARS-CoV-2 during that time period.
In the first week, 49% of the initial viral load samples were considered intermediate, while 25.5% were considered to be low, and the other 25.5% were considered high viral loads. However, as the weeks went on the researchers started to note that the percentages started to shift in favor of the low viral load category.
“By week five of the study, 70% of the positive samples had an initial low viral load” according to a press release. “This trend in initial viral load coincided with a decrease in the percent of deaths. Almost half of the patients in the high viral load group died (45%) compared to 32% and 14% of the intermediate and low viral load categories respectively.”
The authors acknowledged that confounding variables were not accounted for in their observations, but that the findings suggest an association between initial viral load and mortality.
“Exact reasons for a decrease in initial viral load over time are unclear,” said Dr. El Zein, lead study 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 facemasks may have contributed to a decrease in the exposure to the virus."