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In this exclusive MedPage Today video, Theodore Pak, MD, PhD, of Harvard Medical School in Boston, discusses the findings from a study that examined how changes in masking and testing policies in hospitals influenced rates of respiratory viral infections, including COVID-19, influenza, and respiratory syncytial virus (RSV), during the 2023-2024 season.

Following is a transcript of his remarks:

The impetus for this study is that policies for preventing respiratory viral infections in the hospital setting has obviously changed and evolved a lot since the start of the COVID pandemic. And because of the way the pandemic evolved, we often had to implement these changes on the fly. Many hospital systems were figuring out what to do next. It was very unpredictable.

And I think the point of this study is to look at the trend and particularly the last respiratory viral season from 2023 to 2024 and think about what does that mean for what hospitals should consider going forward in terms of masking of staff, masking of patients and visitors, and also testing all patients upon coming to the hospital.

So just to set this up, we had done a study and published it in JAMA Internal Medicine about a year ago, and that reviewed data from the National Health Service, which spans the United Kingdom, but in particular they release a lot of great public data on hospital-onset and community-onset COVID infections at a nationwide level. So it was a very large dataset.

Our health system decided to end universal testing and also universal masking around the same time in May of 2023. So that was about the time the federal public health emergency was ending as well, and general rates of community COVID and other respiratory viruses were on a downtrend at that point going into the summer. So those policy changes occurred, and we decided to do a similar study.

Now we had our own health system, we could use data where we could dig deep into individual cases if necessary, to look at why is testing being performed for this particular patient, what is the clinical background for each case? And we were looking for a very similar thing. What is the association between that policy change and subsequent rates of hospital-onset respiratory viruses? And in this case, we included COVID, influenza, and RSV before and after that policy change.

The rationale for adding more respiratory viruses like flu and RSV is that, last winter, we actually had more of those cases. Those are picking back up again. And our last winter was basically split pretty evenly between flu and COVID in particular, but with still a decent proportion of RSV cases.

So what we saw was that after this policy change occurred, when universal masking and testing ended in our health system, we saw a rise in hospital-onset respiratory and viral infections compared to the number of patients being admitted for those same kind of infections from the community. In an unadjusted model, the change in the ratio is about a doubling, but for these kinds of studies, you do want to adjust for other factors like seasonality, etc. And after doing that, it’s about a 25%, but significant, increase after ending masking and testing compared to the counterfactual of the same trends continuing from the prior period essentially.

And then we were able to add a fourth study period to this analysis because as winter happened last year, of course rates of respiratory viruses started picking back up in the community, and the health system decided to start targeted masking. And what that means is we would have all healthcare staff mask when interacting with patients. These are surgical masks, but it is at least one layer of protection there. And after that policy change, which started January 2024, we were able to collect about 3 months of data. But we did see, using the same model, a 33% drop in hospital-onset respiratory viral infections relative to community-onset infections.

And so, all this goes to show us these two associations where you pull back on precautions and you see a rise, and then you reinstitute some precautions and you see a drop, that these precautions are really tightly associated with changes in hospital-onset infections, and therefore hospitals should really carefully consider them for the coming winter as, no doubt, all these infections pick up again in the community.