There was a positive rate of 9.88 positive results per 100 tests during a 4 month period in 2020, significantly lower than the positivity rate of 29.90 positive results per 100 tests observed for the same date range during the previous 5 virus years.
While some of the public health measures taken by local, state, and federal governments have been unpopular and controversial, shelter-in-place and other public restrictions in the wake of the coronavirus disease 2019 (COVID-19) pandemic may have contributed to less community spread respiratory viruses.
A team, led by Elizabeth Partridge, MD, MPH, Department of Pediatrics, University of California at Davis School of Medicine, examined the association of shelter-in-place orders with lower rates of seasonal respiratory viral activity.
In the cohort study with interrupted time series analysis, the researchers obtained monthly counts of respiratory virus testing results at UC Davis Health between August 2014 and July 2020.
The tests used in the cohort included a respiratory pathogen panel, which tests for influenza A subtypes H1, H1 2019, and H3; influenza B; respiratory syncytial virus (RSV) A and B; parainfluenzavirus 1 to 4; human coronaviruses 229E, HKU1, NL63, and OC43; human metapneumovirus; rhinovirus or enterovirus; and adenovirus.
Patients of all ages underwent testing at the UC Davis Health referral center, which covers a 65,000 square-mile area that includes 33 counties and more than 6 million residents in Northern California.
The statewide shelter-in-place order was instituted in California on March 19, 2020. This order required all residents to be restricted to their homes with the exception of traveling for essential activities. Large social gatherings were banned, with schools and nonessential employment required to occur remotely.
If an individual had to leave their homes they were mandated to wear face masks, engage in frequent handwashing, and maintain physical distancing.
The investigators sought main outcomes of the positivity rates of common respiratory viruses within the community served by UC Davis Health.
A Decrease in Respiratory Viruses
There was a total of 46,128 tests for viral respiratory pathogens over the six-year study, 168 of which occurred during the postexposure period of March 25-July 31, 2020. There was a positive rate of 9.88 positive results per 100 tests during this period, significantly lower than the positivity rate of 29.90 positive results per 100 tests observed for the same date range during the previous 5 virus years.
In addition, the investigators found the positivity rates were similar for the preexposure time frame of August 1, 2019-March 24, 2020 and for the same time periods in the 5 previous years (30.40 vs. 33.68 positive results per 100 tests).
After performing a regression analysis, the investigators found statically significant decreases in viral activity in the postexposure period (93% decrease; incidence rate ratio [IRR], 0.07; 95% CI, 0.02-0.33) and for rhinovirus or enterovirus (81% decrease; IRR, 0.19; 95% CI, 0.09-0.39) infections.
There were also lower rates of postexposure viral activity for respiratory syncytial virus, parainfluenzavirus, coronaviruses, and adenoviruses, but these associations were not deemed to be statistically significant.
“Using interrupted time series analysis of testing for viral respiratory pathogens, this study found that statistically significant lower rates of common community respiratory viruses appeared to be associated with a shelter-in-place order during the coronavirus disease 2019 pandemic,” the authors wrote.
The study, “Evaluation of Seasonal Respiratory Virus Activity Before and After the Statewide COVID-19 Shelter-in-Place Order in Northern California,” was published online in JAMA Network Open.