Lab-positive influenza cases nosedive since March 1

Social distancing, time of year cited as factors in 99 percent decrease
April 17, 2020


The jury’s still out on how well social distancing is working for COVID-19, but it appears to be working wonders against influenza in Delaware.

According to Delaware Health and Social Services flu website, there has been nearly a 99 percent decrease in week-to-week confirmed cases of the flu since the first week in March.

In the DHSS’s current weekly influenza report, issued for the week of March 29 to April 4, there were 6 confirmed cases of the flu. The report issued for the week of March 1 to March 7 showed 439 confirmed cases.

In an interview April 15, Mary Fenimore, Delaware Medical Society manager of communications, said there are a lot of possible variables in play, but she said social distancing is a significant reason for the decrease. She said COVID-19 appears to be much more contagious than influenza and the measures taken to stop the spread of COVID-19 are also working to stop the flu.

“It appears to be an example of why social distancing works,” she said.

Fenimore said closing schools, typically a petri dish for flu as sick kids bring germs to and from home, is limiting transmission. Another factor is the time of year, she said. 

“It’s pretty typical to see a drop this time of year,” she said.

Jennifer Brestel, DHSS spokesperson, confirmed the decrease of confirmed flu cases and also said COVID-19 is much more contagious than the flu. It is very plausible that social distancing measures could be contributing to a decline in flu cases in general, she said.

Brestel also agreed the typical flu season runs from October to May, so it is not surprising to see flu cases declining around this time of year.

The DHSS has weekly influenza reports available on its website dating back to 2008. According to those reports, since 2011, the average decrease in confirmed cases of the flu from week 10 to week 14 is a little more than 50 percent. That percentage does not include this year or 2015, which saw a 5 percent increase in confirmed cases – 19 in week 10; 20 in week 14.

Brestel said it’s also possible that individuals are being diagnosed with flu but are not being tested through a lab. DHSS always notes that the reported data is lab-confirmed cases only, she said.

DHSS knows that there are typically more flu cases in the community than lab-confirmed tests, but individuals may not seek treatment or doctors may diagnose but not order a lab test, said Brestel.

“The flu statistics do not specifically show that individuals are not being treated for flu; it simply shows that lab-confirmed cases of the flu have declined,” said Brestel in an email April 16. “COVID-19 certainly could play a factor in that, but it is difficult to identify a specific cause-and-effect relationship in real time.”

Fenimore said Delaware doctors continue to see patients concerned they have the flu, but she said there’s more telemedicine taking place. It’s another factor to consider, she said.

COVID-19, she said, “has changed our way of living.”

Still, even with the off-the-cliff drop in confirmed flu cases in March, this year will go down as one of the worst flu seasons in Delaware history. Those same weekly influenza reports show 7,075 confirmed cases for the 2019-20 influenza season. That’s the second-highest total behind only the 2017-18 season, which saw 9,050 confirmed cases.

Brestel urged the continued practice of everyday measures to prevent the spread of all respiratory illnesses and infections, including the flu or COVID-19. Those practices include following social-distancing recommendations, staying home if sick with mild symptoms, regular hand washing with soap and water for 20 seconds, not touching the face, and cleaning commonly used surfaces.

Annual comparison of lab-confirmed cases of the flu – week 10 vs week 14:
  • 2019 – week 10, 548 cases; week 14, 130 cases; 76.3 percent decrease
  • 2018 – week 10, 290 cases; week 14, 119 cases; 58.9 percent decrease
  • 2017 – week 10, 319 cases; week 14, 206 cases; 35.4 percent decrease
  • 2016 – week 10, 409 cases; week 14, 132 cases; 67.7 percent decrease
  • 2015 – week 10, 19 cases; week 14, 20 cases; 5.3 percent increase
  • 2014 – week 10, 57 cases; week 14, 55 cases; 3.5 percent decrease
  • 2013 – week 10, 47 cases; week 14, 26 cases; 44.7 percent decrease
  • 2012 – week 10, 35 cases; week 14, 23 cases; 34.3 percent decrease
  • 2011 – week 10, 78 cases; week 14, 15 cases; 80.8 percent decrease  

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