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Effectiveness of Physical Distancing: Staying 6 Feet Over to Put Respiratory Viruses 6 Feet Under

      Abstract

      Community transmission of severe acute respiratory illness Coronavirus-2 (SARS-CoV-2) in Arizona was noted in March 2020. It was our hypothesis that the associated implementation of physical distancing and masking led to a decline in circulation and detection of common respiratory viruses. Nasopharyngeal swabs processed with the Biofire, Film Array respiratory panel at Mayo Clinic Arizona were reviewed from January 1, 2017, to July 31, 2020. A total of 13,324 nasopharyngeal swabs were analyzed. Between April and July 2017- 2019 (Period A) a mean of 262 tests were performed monthly, falling to 128 for the corresponding months of 2020 (Period B). A reduction in the monthly mean number of positive tests (Period A 71.5; Period B 2.8) and mean positivity rate (Period A 25.04%; Period B 2.07%) was observed. Rhinovirus/enterovirus was the most prevalent virus, with a monthly mean of 21.6 cases (30.2% of positives) for Period A and 2 cases (72.7% of positives) for Period B. Positivity for a second virus occurred in a mean of 2.1 positive tests (3.3%) in Period A but was absent in Period B. Implementation of distancing and masking coincides with a marked reduction in respiratory virus detection and likely circulation. Data from the fall/winter of 2020 will help clarify the potential role for distancing and masking as a mitigation strategy, not only for SARS-CoV-2 but also in the seasonal battle against common respiratory viruses.

      Abbreviations and Acronyms:

      CDC (Centers for Disease Control and Prevention), HCoV (human coronavirus), RP (respiratory panel), SARS-CoV-2 (severe acute respiratory illness coronavirus-2)
      National patterns of circulation of the common respiratory viruses, including human coronaviruses (HCoV), influenza, and parainfluenza, are well established. The 4 common HCoV species show peak prevalence between December and March, whereas human parainfluenza viruses show increased prevalence during April to June and October to November each year.
      • Killerby M.E.
      • Biggs H.M.
      • Haynes A.
      • et al.
      Human coronavirus circulation in the United States 2014-2017.
      ,
      • Fry A.M.
      • Curns A.T.
      • Harbour K.
      • Hutwagner L.
      • Holman R.C.
      • Anderson L.J.
      Seasonal trends of human parainfluenza viral infections: United States, 1990-2004.
      Longitudinal studies have shown a consistent, largely predictable pattern of year-on-year disease prevalence.
      • Killerby M.E.
      • Biggs H.M.
      • Haynes A.
      • et al.
      Human coronavirus circulation in the United States 2014-2017.
      The Biofire, FilmArray respiratory (RP) panel (Biofire Diagnostics, Salt Lake City, UT) is performed at Mayo Clinic, Arizona, for detection of respiratory viral pathogens. A pattern of positivity similar to that seen at other testing facilities has been reported previously, with seasonal variation in the circulation of respiratory viral pathogens dropping to a nadir in summer with a predictable increase in positivity thereafter, peaking in the winter months.

      Bolster LaSalle CM, Grys TG. Three year accumulated experience of the BioFire FilmArray Respiratory Panel at a tertiary hospital. Poster presented at: Annual Meeting of the Pan American Society for Clinical Virology and Clinical Virology Symposium, May 19-22, 2016. Daytona Beach, FL.

      Since severe acute respiratory illness coronavirus-2 (SARS-CoV-2) was first reported in December 2019 and later declared a global pandemic, novel measures have been taken to mitigate virus transmission, with physical distancing as a central tenant of these measures. In the United States, the Centers for Disease Control and Prevention (CDC) recommends frequent handwashing, physical distancing of at least 6 feet, and the use of face masks to cover the mouth and nose.
      Centers for Disease Control and Prevention
      How to protect yourself and others.
      The utility of these interventions to reduce the spread of SARS-CoV-2 has been confirmed. However, the influence of these measures on the circulating prevalence of common seasonal respiratory virus pathogens has not been reported in the United States to date.
      It was our hypothesis that the arrival of SARS-CoV-2 community transmission in Arizona and implementation of statewide physical distancing measures coincided with a decline in circulation of the common respiratory viruses. Results obtained from the Biofire, Film Array RP panel performed on nasopharyngeal swabs at Mayo Clinic Arizona were analyzed from January 1, 2017, to July 31, 2020. Three bacteria reported as part of the FilmArray assay were excluded: Chlamydia pneumonia (n = 6), Bordetella pertussis (n = 7), and Mycoplasma pneumonia (n = 22). Indeterminate results were also removed from further analysis (n = 6). A total of 13,324 nasopharyngeal swabs remained available for analysis. Serotypes of influenza A (H1, H1 2009, and H3), non–SARS-CoV-2 coronaviruses (229E, HKU1, NL63, and OC43), and parainfluenza (1-4) were grouped together. For the years 2017 to 2019, the mean number of monthly tests performed between April and July was 262 (range, 137-414). Between April and July 2020, the mean number of tests performed reduced to 128 (range, 92-158). This change was accompanied by an anticipated reduction in the number of positive tests (71.5 for April to July 2017 to 2019 monthly mean versus 2.8 for April to July 2020; Figure 1). During this interval, there was also a marked reduction in the percentage of tests reported positive. The average monthly positivity rate for months between April and July declined from 25.04% for 2017-2019 to 2.07% in the corresponding period of 2020 (Figure 2). Rhinovirus/enterovirus was the most prevalent circulating respiratory virus, detected consistently every month between January 2017 and March 2020, with a mean of 29.9 cases per month (range, 8-68). In 2020, a similar pattern was seen in the first 3 months of the year (mean monthly cases = 36), but only 8 cases of rhinovirus/enterovirus have been detected since the end of March 2020 (Figure 3). A mean of 3.3% of positive test results included positivity for a second viral pathogen in the months April-July from 2017 to 2019. From April of this year onwards, no double positive tests have been reported.
      Figure thumbnail gr1
      Figure 1January 2020 to July 2020 monthly number of positive nasopharyngeal swabs, separated by viral pathogen identified.
      Figure thumbnail gr2
      Figure 2Monthly percentage positive nasopharyngeal swabs from January to July for 2017 to 2020 at Mayo Clinic Arizona. Positivity rates were calculated by dividing the number of positive tests per month by the total number of tests performed each month.
      Figure thumbnail gr3
      Figure 3Monthly number of positive rhinovirus/enterovirus tests between January and July each year, 2017 to 2020 inclusive.
      Our findings are contrary to those reported by Sberna et al in Rome, Italy, who reported similar prevalence levels of seasonal respiratory viruses from February to April 2020, when SARS-CoV-2 community transmission was high, as compared with the corresponding interval of previous years. It should be noted that a different assay was used for viral detection (QIAstat-DX Respiratory Panel; Qiagen).
      • Sberna G.
      • Amendola A.
      • Valli M.B.
      • et al.
      Trend of respiratory pathogens during the COVID-19 epidemic.
      In Taiwan, where physical distancing and mask wearing was swiftly implemented in January 2020, a similar observation to ours has been made in the context of influenzas A and B. The nationwide surveillance data portal for infectious diseases, maintained by the Taiwan Centers for Disease Control, was analyzed for the first 12 weeks of 2020. The analysis demonstrated a significant reduction in the positivity rate for 2020 as compared with the same 12 week interval of 2019.
      • Kuo S.C.
      • Shih S.M.
      • Chien L.H.
      • Hsiung C.A.
      Collateral benefit of COVID-19 control measures on influenza activity, Taiwan.
      Likewise in Singapore, markers of influenza activity (number of daily visits to government primary care clinics with influenza-like illness, number of influenza-like illness samples tested per week, and the percentage of influenza positivity) were markedly lower for epidemiological weeks 5-9 of 2020, when distancing measures were introduced, as compared with the corresponding interval of the preceding 3 years.
      • Soo R.J.J.
      • Chiew C.J.
      • Ma S.
      • Pung R.
      • Lee V.
      Decreased influenza incidence under COVID-19 control measures, Singapore.
      It is worth noting that our laboratory also offered the Focus Simplexa Flu A/B and RSV assay (Focus Diagnostics, Cypress, CA) before January 2019. The use and performance of this assay in tandem with the Biofire RP panel has been reported previously. Outside of influenza season (winter months), the Focus panel was not routinely ordered, with fewer than 20 tests per week. Compared with the BioFire panel, the Focus panel had greater sensitivity for the detection of influenza viruses and lower sensitivity for the detection of RSV.

      Bolster LaSalle CM, Grys TG. Three year accumulated experience of the BioFire FilmArray Respiratory Panel at a tertiary hospital. Poster presented at: Annual Meeting of the Pan American Society for Clinical Virology and Clinical Virology Symposium, May 19-22, 2016. Daytona Beach, FL.

      In January 2019, the Focus panel was replaced, first solely by the COBAS Liat Influenza A/B and RSV assay (Roche Molecular Systems, Pleasanton, CA) and later combined with the Xpert Xpress Flu/RSV assay (Cepheid, Sunnyvale, CA). Both tests have been unavailable at our institution since March 24, 2020. Although detection rates with these 2 assays had not been compared directly with the Biofire RP assay, the use of these assays might have identified additional cases of Influenza A and RSV from March 2020 onwards. Similar to previous years, the use of these tests is anticipated to have been low for the months of interest in 2020 (April-July), given that they fall outside of peak influenza season.
      There are several possible explanations for the decline in the number of tests performed since March of this year. This decline can likely be attributed partly to a reluctance to seek medical care since the onset of the pandemic, with a consequent reduction in health care utilization.
      • Hartnett K.P.
      • Kite-Powell A.
      • DeVies J.
      • et al.
      Impact of the COVID-19 Pandemic on Emergency Department Visits - United States, January 1, 2019-May 30, 2020.
      With the accompanying decline in positivity rate, it is also plausible that physical distancing and face coverings are reducing the transmissibility of the typical seasonal respiratory viruses. Our data are limited to just 4 months (April-July) since community transmission of SARS-CoV-2 became widespread in Arizona in late March 2020. It is anticipated that the respiratory viruses circulate at lower levels during these months, albeit normally higher than what we have seen for 2020 thus far.

      Conclusion

      Clinical laboratory data collected since the arrival of widespread community transmission in Arizona of SARS-CoV-2 demonstrates a reduction in the number of nasopharyngeal swabs being requested and the percentage of positive tests reported. Furthermore, this interval has been characterized by a complete absence of double viral infection and a dramatic reduction in our most consistently prevalent viral pathogen, rhinovirus/enterovirus. The reduction in transmission of these viruses with physical distancing bodes well for the impending fall influenza season. Further analysis of laboratory data as we proceed through the fall and winter of 2020, when an upswing of circulating virus numbers would normally be expected, will help to clarify the potential long-term role for physical distancing and face coverings as a mitigation strategy, not only for SARS-CoV-2 but also in the seasonal battle against common respiratory viral pathogens.

      Supplemental Online Material

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