Nationwide decline in other respiratory pathogens

An interesting but predictable side effect of the coronavirus epidemic is a decline in the prevalence of other respiratory pathogens.

Veteran virus trackers say they are chronicling something never before seen — the suppression of virtually every common respiratory and gastrointestinal virus besides the novel coronavirus. They theorize that is largely due to global shutdowns, mask-wearing and a host of other health protocols aimed at stemming the spread of the coronavirus.

These other viruses — including influenza A, influenza B, parainfluenza, norovirus, respiratory syncytial virus (RSV), human metapneumovirus — all appear to be circulating at or near levels lower than ever previously measured. The same is true for the respiratory bacteria that cause pertussis, better known as whooping cough, and pneumonia...

A year ago at this time, nearly 60 percent of samples taken from patients with flu-like symptoms came back positive for one of the pathogens. But beginning in March of this year, when the coronavirus prompted shutdowns and school closings, the percent of samples positive for any other pathogen took a Grand Canyon-worthy plunge, bottoming out in May at about 6 percent. Even now, at the time of year when respiratory infections typically begin to peak, just 18 percent of samples are positive for any respiratory virus or bacteria...

This decline in prevalence extends beyond the respiratory viruses to include intestinal enteroviruses that are preventable by handwashing.

But there is a downside:

As welcome as the absence of these other viruses is during a pandemic, epidemiologists say they see a potentially dangerous consequence after coronavirus cases eventually decline — a rebound that could be frightfully large given the relaxation of social distancing and lowered immunity to other pathogens.

“The best analogy is to a forest fire,” said Bryan Grenfell, an epidemiologist and population biologist at Princeton. “For the fire to spread, it needs to have unburned wood. For epidemics to spread, they require people who haven’t previously been infected. So if people don’t get infected this year by these viruses, they likely will at some point later on.”..

“It’s a real possibility that we’re going to see increased outbreaks of the endemic infections,” said Ben Lopman, an epidemiologist in Emory University’s Rollins School of Public Health. “If people haven’t gotten infected this year, because of actions taken to prevent covid-19, there’s a real risk of bigger outbreaks when we go back to normal.”

Besides larger-than-normal numbers of endemic infections, Lopman added, some of those infections could be more severe than normal, again because of waning immunity.

More at The Washington Post and chart from BioFire.  It's important not to oversimplify these matters; viral epidemiology is a complex science, and it's easy for people to come to erroneous decisions when they cherry-pick data to support prior assumptions.