SCIENTIFIC
COVID-19 Pandemic Effects on Seasonal Influenza Patterns in West Virginia
AUTHORS : Ryan Demkowicz , MD 1
P . Rocco LaSala , MD 1 Peter Stoilov , PhD 1 James Denvir , PhD 2 Jonathan Moddle 1 Peter L . Perrotta , MD 1
1
Department of Pathology , Anatomy and Laboratory Medicine , West Virginia University School of Medicine
2
The Department of Biomedical Sciences , Marshall University Joan C . Edwards School of Medicine
INTRODUCTION
SARS-CoV-2 and influenza A and B viruses produce respiratory illness and are similarly transmitted through droplets and contact with surfaces harboring virus . West Virginia ( WV ) experiences influenza illnesses that vary in number and severity year by year while generally maintaining a stable seasonal pattern . Influenza cases typically peak during winter months , and epidemics last from 20 to 30 weeks with an incidence historically being estimated at 5-20 %, although recent studies suggest the lower end of this range may be more accurate . 1 , 2
WV was the last state in the United States ( US ) to report a case of SARS-CoV-2 infection at the onset of the COVID-19 pandemic on March 17 , 2020 . 3 Since then , the state has gone through fluctuations of COVID-19 cases as the population was vaccinated and the virus evolved through mutation . Influenza virus activity was reduced in most parts of the world during the COVID-19 pandemic . 4 The reasons for the reduced activity are unclear but may be due to enhanced public health precautions taken to limit the spread of SARS-CoV-2 , including social distancing , wearing of face masks , remote work , and reduced travel .
ABSTRACT
INTRODUCTION The COVID-19 pandemic began in West Virginia ( WV ) in March 2020 at the end of the seasonal increase in influenza virus infections . Diagnostic and surveillance testing for influenza continued throughout the pandemic because these viruses cause similar diseases and the effects of SARS-CoV-2 on seasonal influenza patterns were unpredictable .
METHODS Positivity rates for SARS-CoV-2 and influenza viruses were studied using test results obtained from samples collected across an academic health system from July 2018 through June 2022 . Trends in COVID-19 variants were assessed using data obtained from national and local databases . Data were analyzed to detect differences in and correlations between SARS-CoV-2 and influenza positivity rates .
RESULTS Test positivity rates were higher for the 602,109 SARS-CoV-2 tests than the 186,563
This retrospective study was conducted to examine patterns of SARS-CoV-2 and influenza test positivity across an academic health system centered in a rural state . The effects of the COVID-19 pandemic on seasonal influenza patterns were studied throughout different phases of the pandemic dominated by the different SARS-CoV-2 variants . We hypothesize an inverse relationship between SARS-CoV-2 and influenza virus positivity rates .
METHODS
With local institutional Review Board approval , the daily number of positive and negative tests for SARS-CoV-2 and influenza virus were extracted from the West Virginia University ( WVU ) Medicine integrated electronic health record ( Epic , Madison , WI ) from July 1 , 2018 , through June 17 , 2022 . This time period was chosen to include one pre-pandemic influenza season . Samples were collected influenza tests performed during the study period ( 13.7 % vs . 3.5 %, p < 0.0001 ). SARS-CoV-2 test positivity rose and fell with the emergence of SARS-CoV-2 variants of differing infectivity , being highest when the omicron variant predominated . Significant negative correlations between the number of SARS-CoV-2 and influenza positive tests were seen throughout stages of the pandemic . The normally expected influenza season did not occur during winter 2020 through spring 2021 , and there were essentially no influenza cases during the delta surge . A more typical pattern of seasonal influenza was observed in late 2021 to early 2022 during the omicron surge .
CONCLUSION There was an inverse correlation between SARS-CoV-2 and influenza test positivity rates observed throughout several COVID-19 surges in WV . The reasons for these correlations are unclear .
from across the health system that is predominantly located in WV but extends to Maryland , Pennsylvania , and Ohio .
Testing for SARS-CoV-2 and influenza virus was conducted either in system medical laboratories or at a reference laboratory . Most of the testing was performed at reference laboratories during the first four weeks of the pandemic onset in WV , after which local testing increased to the point where greater than 95 % of testing was performed within the WVU Health System . All viral testing for SARS-CoV-2 was performed using molecular techniques ( e . g ., polymerase chain reaction [ PCR ]); the data does not include testing performed by immunoassays ( i . e ., antigen testing ) or antibody testing ( e . g ., anti-spike or antinucleocapsid ). Most ( 93.4 %) of the influenza tests were performed by molecular techniques , and the remaining were performed using “ rapid ” immunoassays . The
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