Quick Risk Communication Notes on
CDC’s February 29 COVID-19 Presser:
“Absence of Evidence” Portrayed as “Evidence of Absence”

The news peg for the presser was the recently identified U.S. cases of locally transmitted COVID-19 – especially the positive tests in Washington State. So a lot of the presser appropriately focused on details of the recent cases.

But CDC’s Nancy Messonnier explicitly talked about the very few U.S. communities with positive test results as if they were the only U.S. communities with local transmission. She spoke as if “absence of evidence” of local transmission is “evidence of absence” of local transmission. There is absolutely no reason to believe this is true. Days before the first identified community case, we were getting emails from public health officials around the U.S. decrying the test eligibility and availability scandal, and saying they were virtually certain that community transmission was occurring in their locations. Dr. Messonnier claimed repeatedly that the risk of current, ongoing COVID-19 transmission is low in any community that has no positive test results. There is no way that she could know this. And it seems unlikely that she believes it.

The pretense that “absence of evidence is evidence of absence” is profoundly misleading and disingenuous since most communities’ COVID-19 test status is zero for zero. Zero positive tests, zero negative tests, zero total tests. For nearly all U.S. cities and towns, “no positive results” is the only possible outcome because there have been no tests. The absence of positive tests in such communities should not be portrayed as reassuring. It is dishonest to do so. At any given time, most communities have people with unexplained respiratory symptoms, some of whom might have COVID-19 and might have been transmitting it to others. Eventually, some of them may be tested. CDC’s advice today made it sound as if they had already tested negative. You might as well say that the Lakers have scored no baskets so far, when the game isn’t until tomorrow.

The pretense that “absence of evidence is evidence of absence” is especially culpable coming from the federal agency most responsible (along with the FDA) for the fact that most community’s test status so far is zero for zero. The federal government that failed to provide test kits and failed to allow local testing is now saying your community’s risk is low if there are no local positive test results.

The “community transmission” meaning of a positive test result depends partly on how many tests have been conducted that came out negative. Washington State reported two positive test results today. How many negative test results does it have? Two out of two thousand would be reassuring. Two out of two would be alarming. Today’s presser did not provide this crucial information. Similarly, when Dr. Messonnier says that the risk in the rest of the country remains low, every reporter should ask: How many tests have been done in each state so far? How many turned out negative? How many positive? CDC has required every test so far (as of February 29) to be forwarded to them for confirmation – so CDC knows the answer to this question.

Public health policy in the United States is set mostly by state and local officials. But state and local officials almost always follow the advice of CDC. Usually that is good advice. Today it is questionable advice: Continue business as usual until you get your very own positive test result.

To her credit, Dr. Messonnier reiterated the warning that the U.S. may see widespread transmission. To her discredit, she discounted the likelihood that the U.S. may already have areas with widespread transmission that are not visible yet. And she advised no new immediate community precautions (banning most hospital visits, for instance) against that possibility.

At her next presser, Dr. Messonnier could say, “While communities wait for evidence about whether they have local COVID-19 transmission already, local officials should consider additional social distancing precautions to take now or soon against the possibility that the news will be bad. And they should start now to prepare their publics for that possibility, and for further social distancing precautions down the road.” That is what it looks like not to downplay the risk, or discount the near-term future.

Dr. Messonnier made evergreen business-as-usual recommendations – like staying home when you are sick – sound less urgent than they are in the face of COVID-19. Everyone knows that most people don’t stay home when they are mildly ill. “These precautions take on new urgency in the face of this new threat of unknown severity,” she might have said. “Too many of us shrug off this advice in ordinary times. We should all take it to heart now.”

As risk communicators, we obviously have no professional role in predicting the course of any outbreak. But having worked on pandemic planning with governments and international agencies all around the world, we believe that most experts think the U.S. is unlikely to avoid widespread transmission. This is the context for our generic advice: Officials should always vividly focus on the likeliest scenario (in this case, we think, widespread transmission) and the “credible worst case scenario” (the worst outcome that isn’t vanishingly unlikely). CDC spoke today as if the best case scenario – transmission in only a few communities – were the likeliest scenario. Even if they cannot force themselves to talk at all about credible worst-case scenarios, officials must proclaim the most likely scenario, not just whisper it or hint at it. After that, it’s okay to mention the best-case scenario – but only briefly, and as an expression of hope that we all share.

In moments of crisis, leadership requires messages of determination and hope, not optimism. We haven’t seen that yet from the President, and we didn’t see it today from CDC. If and when tens of thousands of U.S. tests have been conducted in communities across our land, and nearly all are negative, messages of optimism will be justified. Even then, the optimism should be tentative: “We’re not out of the woods yet.”

We laughed with a tinge of anger when Dr. Messonnier said that “from the beginning” CDC has been encouraging local clinicians to use their own discretion in deciding whom to test. Seattle/King County’s Jeff Duchin was clear in the presser that his agency was only recently able to do any testing, using very recently expanded testing eligibility. But revisionist history is a minor sin compared to over-optimistic advice to state and local officials, and over-optimistic reassurance to the public at large.

Dr. Messonnier did acknowledge public concern, which is better than not acknowledging public concern. But we would like to see officials escalate their rhetoric beyond “concern,” which sounds mealy-mouthed to frightened people. Paul Revere did not ride to every village and farm to spread the “concern” that the British were coming. Is there anyone in all of government who is not at least “alarmed” about what is happening and what may happen? More importantly, we would like to see officials show that they share the alarm. This is not a time for a calm “us” to be placating a frightened “you.” It is a time for all of us to calmly, determinedly, bear our fear together. Instead of expressing their “understanding” that others are “concerned,” officials at COVID-19 press briefings should try to talk about an inclusive “we” who are rightly alarmed and bearing our fear as we face this emergency together.

Some countries that started with a few positive tests now have widespread outbreaks. It seems likely that the U.S. will follow this path. Now is the time for CDC officials to say publicly that if we follow the path of Italy and others, here is how we will try to reduce the burden on healthcare systems, and here is what the public can do. Whatever social distancing precautions are appropriate now, warn people that these may be dramatically ramped up. Help the public prepare emotionally and logistically for the more stringent and unprecedented precautions that may be coming.

At her presser on February 25, Nancy Messonnier did the best COVID-19 risk communication we have seen from a U.S. government official so far. (Tony Fauci of NIH has had some excellent moments as well.) Hours later, HHS Secretary Azar and President Trump took U.S. COVID-19 risk communication in a different direction, toward drastic over-reassurance and downplaying of the risk. So Dr. Messonnier’s messaging today may be the best she is permitted. Our criticism is about her repeated messages to the effect that communities without positive test results have no community transmission of COVID-19 – that absence of evidence is evidence of absence. That is what she communicated. That is the impression we got. We have no idea what she really wanted to say.