COVID-19 public health interventions reduced other respiratory infections

Wearing masks and being quarantined while sick has helped mitigate the spread of Coronavirus 2 (SARS-CoV-2) with severe acute respiratory syndrome. An indirect benefit of these efforts appears to be a decrease in the incidence of flu and other respiratory infections. New research, led by Lisa G. Winston of the University of California at San Francisco, confirmed that public health interventions from COVID-19 helped reduce the number of airborne viruses.

The results suggest that public health COVID guidelines like masking are non-pharmaceutical means to help reduce respiratory illnesses in the future. The researchers find that these interventions remained helpful even as people gathered more outside.

“While our results complement the evidence for effective disease reduction strategies, it is also noteworthy that the low rate of respiratory virus detection remained low during intermittent months of increased public interaction and movement in the Bay Area, including periods when companies were partially approved were reopening, periods of civil protests and periods of increased summer outdoor activities. This suggests a central role in masking and reducing the accumulation of enclosed spaces to disrupt the transmission of respiratory viruses. “

The study “Significant and sustained decrease in non-SARS-CoV-2 viral infections of the respiratory tract during COVID-19 public health interventions” is available as a preprint on the medRxiv * server while the article was peer-reviewed becomes.

How they did it

In San Francisco Bay, a protection ordinance was issued on March 16, 2020 with a mask mandate implemented on April 17, 2020. The researchers collected information on airborne viruses in the area from January 2019 to December 2020 to compare the prevalence of respiratory viruses a year before and during the pandemic.

They used a respiratory pathogen panel assay – for the detection of infectious respiratory viruses – from the Zuckerberg San Francisco General Hospital’s clinical laboratory information system to screen 17 viral pathogens and 4 bacterial organisms. The researchers analyzed monthly trends of positive results for non-SARS-CoV-2 respiratory pathogens.

Proportion of positive respiratory pathogen tests per month in 2019 compared to 2020. Proportion of positive tests in 2019 and 2020 by month.  The diagnosis of viral diseases of the respiratory tract became significantly less frequent from March to April 2020, and from April to December 2020 the percentage of positive tests was consistently lower compared to the corresponding month in 2019.  NS, not significant;  *, P <0.05;  **, P <0.01;  ***, P <0.001;  ****, p <0.0001.  a Shelter-in-Place came into force on March 16, 2020.  b The Masking Ordinance came into force on April 17, 2020.

Proportion of positive respiratory pathogen tests per month in 2019 compared to 2020. Proportion of positive tests in 2019 and 2020 by month. The diagnosis of viral respiratory diseases became significantly rarer from March to April 2020, and from April to December 2020 the percentage of positive tests was consistently lower compared to the corresponding month in 2019. NS, not significant; *, P <0.05; **, P <0.01; ***, P <0.001; ****, p <0.0001. a Shelter-in-Place came into force on March 16, 2020. b The Masking Ordinance came into force on April 17, 2020.

Decrease in non-COVID respiratory infections

The researchers rated 1,484 tests in 2019 and 2,037 tests in 2020. The tests between January 2019 and March 2020 were between 13.6% and 39.1% positive for a respiratory infection.

April to December 2020 was the period during the COVID-19 pandemic. Respiratory infections decreased with a positivity rate of 0 to 11.1% for non-SARS-CoV-2 infections.

“The proportion of overall positive tests was not significantly different in January, February and March 2019 compared to the same months in 2020. However, the percentage of positive tests was lower during the COVID-19 restrictions for each month from April to December 2020 compared to 2019, “the researchers wrote.

The human rhinoviruses / enteroviruses were detected most frequently of all respiratory viruses. Approximately 89.6% of positive test results for respiratory infections were from human rhinovirus / enterovirus during the pandemic compared to 55% in 2019.

The San Francisco data showed no cases of influenza for the 2020-2021 flu season.

Study restrictions

Certain study restrictions could have affected the results. The research design involved examining 2-year data from a single health system that may not be transferable to other parts of the city with varying degrees of respiratory infections. There may be other confusions too, such as: E.g. a person’s population or masking compliance, which can affect the results. In addition, changes in indoor policy restrictions in response to rising cases or increased vaccinations can result in significant fluctuations in monthly airway transmission.

People may also have experienced respiratory infections like the flu but were too anxious to seek medical help during the pandemic. “Nonetheless, our focus should be on inpatients who have been tested for respiratory infections, rather than the larger number of outpatients, which should reduce the differences in testing practices that can arise in dealing with a mild and undifferentiated disease.”

It remains unclear which guideline or combination of guidelines was most effective at reducing the number of respiratory infections. The researchers conclude that finding the answer to this question could help develop public health strategies to reduce breath droplet transmission at home, in public, or even at work.

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

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