Your Community and COVID-19: How to Make Sense of the Numbers Where You Live
A map of cumulative known cases of COVID-19 in the U.S., as of June 12th, 2020.
Have you felt a bit like an armchair epidemiologist lately? Maybe you've been poring over coronavirus statistics on your county health department's website or on the pages of your local newspaper.
If the percentage of positive tests steadily stays under 8 percent, that's generally a good sign.
You're likely to find numbers and charts but little guidance about how to interpret them, let alone use them to make day-to-day decisions about pandemic safety precautions.
Enter the gurus. We asked several experts to provide guidance for laypeople about how to navigate the numbers. Here's a look at several common COVID-19 statistics along with tips about how to understand them.
Case Counts: Consider the Context
The number of confirmed COVID-19 cases in American counties is widely available. Local and state health departments should provide them online, or you can easily look them up at The New York Times' coronavirus database. However, you need to be cautious about interpreting them.
"Case counts are the obvious numbers to look at. But they're probably the hardest thing to sort out," said Dr. Jeff Martin, an epidemiologist at the University of California at San Francisco.
That's because case counts by themselves aren't a good window into how the coronavirus is affecting your community since they rely on testing. And testing itself varies widely from day to day and community to community.
"The more testing that's done, the more infections you'll pick up," explained Dr. F. Perry Wilson, a physician at Yale University. The numbers can also be thrown off when tests are limited to certain groups of people.
"If the tests are being mostly given to people with a high probability of having been infected -- for example, they have had symptoms or work in a high-risk setting -- then we expect lots of the tests to be positive. But that doesn't tell us what proportion of the general public is likely to have been infected," said Eleanor Murray, an epidemiologist at Boston University.
These Stats Are More Meaningful
According to Dr. Wilson, it's more useful to keep two other statistics in mind: the number of COVID tests that are being performed in your community and the percentage that turn up positive, showing that people have the disease. (These numbers may or may not be available locally. Check the websites of your community's health department and local news media outlets.)
If the number of people being tested is going up, but the percentage of positive tests is going down, Dr. Wilson said, that's a good sign. But if both numbers are going up – the number of people tested and the percentage of positive results – then "that's a sign that there are more infections burning in the community."
It's especially worrisome if the percentage of positive cases is growing compared to previous days or weeks, he said. According to him, that's a warning of a "high-risk situation."
Dr. George Rutherford, an epidemiologist at University of California at San Francisco, offered this tip: If the percentage of positive tests steadily stays under 8 percent, that's generally a good sign.
There's one more caveat about case counts. It takes an average of a week for someone to be infected with COVID-19, develop symptoms, and get tested, Dr. Rutherford said. It can take an additional several days for those test results to be reported to the county health department. This means that case numbers don't represent infections happening right now, but instead are a picture of the state of the pandemic more than a week ago.
Hospitalizations: Focus on Current Statistics
You should be able to find numbers about how many people in your community are currently hospitalized – or have been hospitalized – with diagnoses of COVID-19. But experts say these numbers aren't especially revealing unless you're able to see the number of new hospitalizations over time and track whether they're rising or falling. This number often isn't publicly available, however.
If new hospitalizations are increasing, "you may want to react by being more careful yourself."
And there's an important caveat: "The problem with hospitalizations is that they do lag," UC San Francisco's Dr. Martin said, since it takes time for someone to become ill enough to need to be hospitalized. "They tell you how much virus was being transmitted in your community 2 or 2.5 weeks ago."
Also, he said, people should be cautious about comparing new hospitalization rates between communities unless they're adjusted to account for the number of more-vulnerable older people.
Still, if new hospitalizations are increasing, he said, "you may want to react by being more careful yourself."
Deaths: They're an Even More Delayed Headline
Cable news networks obsessively track the number of coronavirus deaths nationwide, and death counts for every county in the country are available online. Local health departments and media websites may provide charts tracking the growth in deaths over time in your community.
But while death rates offer insight into the disease's horrific toll, they're not useful as an instant snapshot of the pandemic in your community because severely ill patients are typically sick for weeks. Instead, think of them as a delayed headline.
"These numbers don't tell you what's happening today. They tell you how much virus was being transmitted 3-4 weeks ago," Dr. Martin said.
'Reproduction Value': It May Be Revealing
You're not likely to find an available "reproduction value" for your community, but it is available for your state and may be useful.
A reproduction value, also known as R0 or R-naught, "tells us how many people on average we expect will be infected from a single case if we don't take any measures to intervene and if no one has been infected before," said Boston University's Murray.
As The New York Times explained, "R0 is messier than it might look. It is built on hard science, forensic investigation, complex mathematical models — and often a good deal of guesswork. It can vary radically from place to place and day to day, pushed up or down by local conditions and human behavior."
It may be impossible to find the R0 for your community. However, a website created by data specialists is providing updated estimates of a related number -- effective reproduction number, or Rt – for each state. (The R0 refers to how infectious the disease is in general and if precautions aren't taken. The Rt measures its infectiousness at a specific time – the "t" in Rt.) The site is at rt.live.
"The main thing to look at is whether the number is bigger than 1, meaning the outbreak is currently growing in your area, or smaller than 1, meaning the outbreak is currently decreasing in your area," Murray said. "It's also important to remember that this number depends on the prevention measures your community is taking. If the Rt is estimated to be 0.9 in your area and you are currently under lockdown, then to keep it below 1 you may need to remain under lockdown. Relaxing the lockdown could mean that Rt increases above 1 again."
"Whether they're on the upswing or downswing, no state is safe enough to ignore the precautions about mask wearing and social distancing."
Keep in mind that you can still become infected even if an outbreak in your community appears to be slowing. Low risk doesn't mean no risk.
Putting It All Together: Why the Numbers Matter
So you've reviewed COVID-19 statistics in your community. Now what?
Dr. Wilson suggests using the data to remind yourself that the coronavirus pandemic "is still out there. You need to take it seriously and continue precautions," he said. "Whether they're on the upswing or downswing, no state is safe enough to ignore the precautions about mask wearing and social distancing. 'My state is doing well, no one I know is sick, is it time to have a dinner party?' No."
He also recommends that laypeople avoid tracking COVID-19 statistics every day. "Check in once a week or twice a month to see how things are going," he suggested. "Don't stress too much. Just let it remind you to put that mask on before you get out of your car [and are around others]."
In this week's Friday Five, an old diabetes drug finds an exciting new purpose. Plus, how to make the cities of the future less toxic, making old mice younger with EVs, a new reason for mysterious stillbirths - and much more.
The Friday Five covers five stories in research that you may have missed this week. There are plenty of controversies and troubling ethical issues in science – and we get into many of them in our online magazine – but this news roundup focuses on scientific creativity and progress to give you a therapeutic dose of inspiration headed into the weekend.
Here is the promising research covered in this week's Friday Five:
Listen on Apple | Listen on Spotify | Listen on Stitcher | Listen on Amazon | Listen on Google
- How to make cities of the future less noisy
- An old diabetes drug could have a new purpose: treating an irregular heartbeat
- A new reason for mysterious stillbirths
- Making old mice younger with EVs
- No pain - or mucus - no gain
And an honorable mention this week: How treatments for depression can change the structure of the brain
Researchers at Stanford have found that the virus that causes Covid-19 can infect fat cells, which could help explain why obesity is linked to worse outcomes for those who catch Covid-19.
Obesity is a risk factor for worse outcomes for a variety of medical conditions ranging from cancer to Covid-19. Most experts attribute it simply to underlying low-grade inflammation and added weight that make breathing more difficult.
Now researchers have found a more direct reason: SARS-CoV-2, the virus that causes Covid-19, can infect adipocytes, more commonly known as fat cells, and macrophages, immune cells that are part of the broader matrix of cells that support fat tissue. Stanford University researchers Catherine Blish and Tracey McLaughlin are senior authors of the study.
Most of us think of fat as the spare tire that can accumulate around the middle as we age, but fat also is present closer to most internal organs. McLaughlin's research has focused on epicardial fat, “which sits right on top of the heart with no physical barrier at all,” she says. So if that fat got infected and inflamed, it might directly affect the heart.” That could help explain cardiovascular problems associated with Covid-19 infections.
Looking at tissue taken from autopsy, there was evidence of SARS-CoV-2 virus inside the fat cells as well as surrounding inflammation. In fat cells and immune cells harvested from health humans, infection in the laboratory drove "an inflammatory response, particularly in the macrophages…They secreted proteins that are typically seen in a cytokine storm” where the immune response runs amok with potential life-threatening consequences. This suggests to McLaughlin “that there could be a regional and even a systemic inflammatory response following infection in fat.”
It is easy to see how the airborne SARS-CoV-2 virus infects the nose and lungs, but how does it get into fat tissue? That is a mystery and the source of ample speculation.
The macrophages studied by McLaughlin and Blish were spewing out inflammatory proteins, While the the virus within them was replicating, the new viral particles were not able to replicate within those cells. It was a different story in the fat cells. “When [the virus] gets into the fat cells, it not only replicates, it's a productive infection, which means the resulting viral particles can infect another cell,” including microphages, McLaughlin explains. It seems to be a symbiotic tango of the virus between the two cell types that keeps the cycle going.
It is easy to see how the airborne SARS-CoV-2 virus infects the nose and lungs, but how does it get into fat tissue? That is a mystery and the source of ample speculation.
Macrophages are mobile; they engulf and carry invading pathogens to lymphoid tissue in the lymph nodes, tonsils and elsewhere in the body to alert T cells of the immune system to the pathogen. Perhaps some of them also carry the virus through the bloodstream to more distant tissue.
ACE2 receptors are the means by which SARS-CoV-2 latches on to and enters most cells. They are not thought to be common on fat cells, so initially most researchers thought it unlikely they would become infected.
However, while some cell receptors always sit on the surface of the cell, other receptors are expressed on the surface only under certain conditions. Philipp Scherer, a professor of internal medicine and director of the Touchstone Diabetes Center at the University of Texas Southwestern Medical Center, suggests that, in people who have obesity, “There might be higher levels of dysfunctional [fat cells] that facilitate entry of the virus,” either through transiently expressed ACE2 or other receptors. Inflammatory proteins generated by macrophages might contribute to this process.
Another hypothesis is that viral RNA might be smuggled into fat cells as cargo in small bits of material called extracellular vesicles, or EVs, that can travel between cells. Other researchers have shown that when EVs express ACE2 receptors, they can act as decoys for SARS-CoV-2, where the virus binds to them rather than a cell. These scientists are working to create drugs that mimic this decoy effect as an approach to therapy.
Do fat cells play a role in Long Covid? “Fat cells are a great place to hide. You have all the energy you need and fat cells turn over very slowly; they have a half-life of ten years,” says Scherer. Observational studies suggest that acute Covid-19 can trigger the onset of diabetes especially in people who are overweight, and that patients taking medicines to regulate their diabetes “were actually quite protective” against acute Covid-19. Scherer has funding to study the risks and benefits of those drugs in animal models of Long Covid.
McLaughlin says there are two areas of potential concern with fat tissue and Long Covid. One is that this tissue might serve as a “big reservoir where the virus continues to replicate and is sent out” to other parts of the body. The second is that inflammation due to infected fat cells and macrophages can result in fibrosis or scar tissue forming around organs, inhibiting their function. Once scar tissue forms, the tissue damage becomes more difficult to repair.
Current Covid-19 treatments work by stopping the virus from entering cells through the ACE2 receptor, so they likely would have no effect on virus that uses a different mechanism. That means another approach will have to be developed to complement the treatments we already have. So the best advice McLaughlin can offer today is to keep current on vaccinations and boosters and lose weight to reduce the risk associated with obesity.