COVID-19 restrictions tied to lower rates of respiratory viruses in the community

Shelter-in-place orders at the start of the COVID-19 pandemic in the U.S. appear to be associated with significantly lower rates of common community respiratory viruses, including influenza and rhinovirus.

“The end of the 2019-2020 respiratory virus season presented a unique opportunity to evaluate the outcome of public health interventions in response to SARS-CoV-2 for the epidemiologic characteristics of other circulating respiratory viruses,” Elizabeth Partridge, MD, pediatrics specialist in the department of infectious diseases and assistant clinical professor at UC Davis School of Medicine in Sacramento, California, and colleagues wrote in JAMA Network Open. “Public health initiatives that include shelter-in-place orders are expensive and unpopular. Demonstrating their success is essential to justify their systemic or individual cost.”

The researchers conducted a cohort study to evaluate positivity rates of common respiratory viruses in the community served by UC Davis Health from August 2014 to July 2020. Partridge and colleagues examined 46,128 test results for viral respiratory pathogens during the 6-year period performed at UC Davis Health.

The researchers then evaluated test results before and after the statewide stay-at-home order began in March 2020.

During the postexposure period from March to July 2020, there were 168 positive test results for viral respiratory pathogens, with a positivity rate of 9.88 positive results per 100 tests, which was lower than the positivity rate of 29.9 positive results per 100 tests during the previous five respiratory virus seasons. Positivity rates were similar in the preexposure period of August to March 2020 and for the respiratory virus seasons in the previous 5 years (30.4 vs. 33.68 positive results per 100 tests).

Researchers observed significant decreases in respiratory viral activity in the postexposure period, with a 93% decrease in influenza cases (incidence rate ratio [IRR] = 0.07; 95% CI, 0.02-0.33; P = .001) and an 81% decrease in rhinovirus or enterovirus cases (IRR = 0.19; 95% CI, 0.09-0.39; P < .001). The researchers also reported lower rates of respiratory syncytial virus (67% reduction; IRR = 0.33; 95% CI, 0.1-1.1; P = .07), parainfluenza virus (91% reduction; IRR = 0.9; 95% CI, 0.01-1.25; P = .07), coronavirus (IRR = 0.37; 95% CI, 0.06-2.52; P = .3) and adenovirus (IRR = 0.23; 95% CI, 0.04-1.23; P = .08) during the postexposure viral activity period.

“The restrictions on travel, mandated mask wearing and physical distancing that are embedded in the California shelter-in-place order have been controversial because of their substantial social and economic costs,” the researchers wrote. “However, this cohort study shows that public health strategies have been associated with lower rates of respiratory viruses in the community served by UC Davis Health.”