[Note: This item comes from friend David Rosenthal. DLH]
What We Need to Understand About Asymptomatic Carriers if We’re Going to Beat Coronavirus
ProPublica’s health reporter Caroline Chen explains what the conversation around asymptomatic coronavirus carriers is missing, and what we need to understand if we’re going to beat this nefarious virus together.
By Caroline Chen
Apr 2 2020
https://www.propublica.org/article/what-we-need-to-understand-about-asymptomatic-carriers-if-were-going-to-beat-coronavirus
In the early days of the coronavirus outbreak in the U.S., around the last week of February, I joked to a colleague that maybe now, finally, people would learn how to wash their hands properly. My remark revealed a naive assumption I had at the time, which was that all we needed to do to keep the novel coronavirus contained was follow a few simple guidelines: stay home when symptomatic and maintain good personal hygiene. The problem, I thought, was that nobody was following the rules.
In the past few weeks, however, more and more reports have emerged to challenge my neat assumptions. Seven out of 14 NBA players, coaches and staff who tested positive didn’t have symptoms when they were diagnosed, The Wall Street Journal reported. The U.S. Centers for Disease Control and Prevention issued a case study on a nursing facility in King County, Washington, where 23 residents tested positive for COVID-19, and it found that 13 reported no symptoms initially. Sixty singers went to rehearsal and followed all the rules, according to the Los Angeles Times — nobody hugged, shook hands or appeared ill — yet three weeks later, 45 were diagnosed with COVID-19 or had symptoms of the disease, and two have died.
With articles about “silent spreaders” and “stealth transmission” flying across the internet, friends were starting to text me: Was it still OK to go for a walk with a friend, even 6 feet apart? Or should all interaction be avoided? Should we start wearing masks to the grocery store? At the same time, my colleagues were scrutinizing guidelines at various workplaces and agencies we cover: The New York City Fire Department told workers on March 19 they were to come to work, so long as they had no symptoms, even if they had had “close contact with someone who is a known positive COVID-19 patient,” according to a document obtained by ProPublica. Was that policy wise?
I decided to dive into the available data. What I discovered is that not only can people be infected and experience no symptoms or very mild symptoms for the first few days, but this coincides with when the so-called viral load — the amount of virus being emitted from an infected person’s cells — may be the highest. That makes the virus a truly formidable opponent in our densely packed, globally connected world. We’re going to have to be smarter than this virus to stay on top of it.
What does asymptomatic really mean?
Let’s start with the basics. Dr. Maria Van Kerkhove, head of the emerging diseases and zoonoses unit at the World Health Organization, told me that the WHO so far has found few truly asymptomatic cases, in which a patient tests positive and has zero symptoms for the entire course of the disease. However, there are many cases where people are “pre-symptomatic,” where they have no symptoms at the time when they test positive but go on to develop symptoms later.
“Most of the people who were thought to be asymptomatic aren’t truly asymptomatic,” said Van Kerkhove. “When we went back and interviewed them, most of them said, actually I didn’t feel well but I didn’t think it was an important thing to mention. I had a low-grade temperature, or aches, but I didn’t think that counted.”
The WHO sent a team to China and visited community centers, clinics and hospitals, and transportation hubs. Through their data collection, the team found that about 75% of people who were initially classified as “asymptomatic” went on to develop symptoms, she said. This matches up with the CDC’s findings at the nursing facility in Washington. Of the 13 positive patients who initially reported no symptoms during testing,10 later developed symptoms.
But ultimately, the only way to really find out how many asymptomatic COVID-19 carriers are out there would be to conduct blood tests across large swaths of the population to look for antibodies, which are a type of protein that provide evidence that a person’s immune system did battle with the coronavirus. Tests that can look for these antibodies are now being developed in several countries.
For the purposes of containing the outbreak right now, however, Jeffrey Shaman, a professor of environmental health sciences at Columbia University’s Mailman School of Public Health, says the focus on asymptomatics is a bit of a red herring.
“In some sense, symptomatic versus asymptomatic isn’t really the appropriate dividing line” for us to be focusing on, he said. “The appropriate dividing line is documented versus undocumented infection.”
What Shaman means by “documented” is people who are identified as being infected, either because they were sick enough to go seek care or were tested through contact tracing, which is when public health officials track down all the contacts of someone who tested positive. The “undocumented” could be people who have symptoms but didn’t get tested, because of lack of access to testing, dislike of doctors or sheer stoicism — or more concerningly, people who had no symptoms or such mild symptoms that they decided to just carry on with their daily lives.
“Maybe they pop some ibuprofen, but still go to work, still get on public transportation, still do all the things we normally do, and the consequence of that is those people with mild infections — as well as if they’re truly asymptomatic — are taking the virus out into the community, and they’re spreading it far and wide,” Shaman said.
Shaman and colleagues published a study in the journal Science on March 16 in which, using a statistical model, they estimated that 86% of all infections in China were “undocumented” prior to Jan. 23, when Chinese authorities cut off Wuhan, canceling all planes and trains leaving the city. This would help explain the rapid spread of the virus across the country, they said, concluding that their findings “indicate containment of this virus will be particularly challenging.”
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