This weekend, as it became clearer and clearer that Covid-19 has been spreading stealthily through the Pacific Northwest, the task facing health officials has become more and more monumental. To try to stop the virus’ transmission and restrain the outbreak, they need to identify every single person with whom patients have come into contact, isolate those at risk of harboring the illness, and monitor the entire network of people for symptoms.
That’s hard even if you know how each patient became infected. If you don’t, it can be downright herculean. The fact that the pathogen is passing through people without making them sick enough to seek care means that they may have unwittingly transmitted it for weeks before it came to the attention of authorities. Once a case is discovered, epidemiologists still need to figure out whom the patient might have exposed. But they also need to look in the other direction, too, to figure out by what unseen route the virus reached that person in the first place.
“The question is, what is their source of exposure?” said Laurence Burnsed, state epidemiologist for Oklahoma’s health department. “Who are we missing?”
Answering such questions requires state and county health agencies — overworked as they already are — to ramp up their efforts as fast as possible.
“Speed is critical. Speed is absolutely critical. Every country that is receiving their first cases needs to act robustly and aggressively. … Look for this virus,” said Maria Van Kerkhove, head of the emerging diseases and zoonoses unit for the World Health Organization’s global infectious hazard preparedness team, in an interview with STAT.
Controlling the outbreak means getting ahead of the virus — and that’s no mean feat in a situation shifting so rapidly.
On Friday night, there were reports of four people — two in California, one in Oregon, and one in Washington State — who’d tested positive for the virus but had neither a known history of traveling outside the U.S. nor any identified contact with previously diagnosed patients. By Saturday afternoon, officials reported an outbreak of the virus in a long-term care facility outside of Seattle as well as the first death in the U.S. due to the illness — but it wasn’t clear whether those two events were related.
“That’s the kind of thing that we’re trying to answer now,” said Jeffrey Duchin, health officer for public health for Seattle and King County in a Saturday press briefing. “We’re doing an investigation as we speak to try and understand all the potential exposures that that patient may have had and if there’s any potential commonalities … but at this point we don’t have links.”
By Saturday night virologists had sequenced samples from one of the mysteriously acquired Covid-19 cases in Washington State, and found that the pathogen looked like a descendent of the virus swabbed from the first reported case in the U.S., identified way back on January 16. But there was no known contact between the two patients.
“There are some enormous implications here,” tweeted Trevor Bedford, a researcher at Fred Hutchinson Cancer Research Center in Seattle, who studies how viruses evolve and spread. “This strongly suggests there has been cryptic transmission in Washington State for the past 6 weeks.”
But genetic sequencing data come from already diagnosed cases. That can’t help you find people whose infections have gone undetected.
For that, you need the old-fashioned detective work of contact tracing.
It begins with an in-depth interview. An official sits down with a patient, and together, they reconstruct exactly where that person has been and with whom, day by day, hour by hour, for the entire window of potential contagion. The conversation often lasts hours. “That would be having the case pull out their personal calendar, going through their phone,” Burnsed said. “They might even have to go through their social media feed to see where they were tagged and what they did, to kind of jog their memory.”
The officials try to identify every single person who might have been unwittingly exposed to the pathogen. They start with family members and close friends — but then, as Burnsed put it, “the next level is identifying all of the contacts in shared airspaces.” Did you go to restaurants? What time were you there? Did you go to work or school? Did you take your child to daycare? Did you go see a doctor?
It’s already enough work to try to identify everyone who might have been at a hospital at the same time as that person — pulling rosters of on-shift workers, asking for appointment times of other patients, trying to figure out if they were there with family members. Other public spaces can be harder, because there are less meticulous records of who was where when.
Once officials have reached everyone they can reach, they still need to monitor them, and if they are at risk of spreading the illness, make sure they isolate themselves. Even for a handful of cases, it’s an unwieldy operation: When Oklahoma identified four measles diagnoses last year, the health department had to assess 300 individuals, Burnsed said.
While Covid-19 is less contagious than measles, the effort required for contact tracing investigations last year illuminates the sort of scramble Washington state officials are facing now. In a single nursing facility alone, some 50 people —including both staff and residents — have symptoms and are undergoing testing for the virus, and those aren’t the only potential cases.
The sheer number of people to reach won’t be the only issue. “Challenges in any large outbreak involve fully identifying all contacts including those that may have been exposed in a more public setting (and who are not known by name), insufficient or incorrect contact information given that hinders finding contacts, and lack of compliance by identified contacts,” Sharon Watkins, Pennsylvania’s state epidemiologist, wrote in an email to STAT.
That issue can be especially prevalent for vulnerable groups, such a undocumented immigrants, who worry that identifying themselves to health authorities might make their situations even more precarious.
In American Samoa, for instance, during the measles outbreak that began late in 2019, some people from the nearby Independent State of Samoa, as well from Tonga, Fiji, the Philippines, China, and Korea, were worried that participating in contact investigations might jeopardize their immigration status .
“Some of these population groups are close knit and will not easily reveal who in their community are or were sick with measles,” explained American Samoa Health Department Epidemiologist Aifili John Tufa, in a text message. “They are afraid that if they tell our team they may be ‘incriminating’ their own.”
Yet, to the WHO’s Van Kerkhove, in spite of these challenges, it’s imperative that public health officials in the US and around the world race to track and control the virus’ spread. “What worries me the most is people feeling like there’s nothing that they can do and they just have to give up and surrender to this virus … and we just have to let the wave pass through,” she said.
She is hopeful that by identifying and isolating potential Covid-19 patients, health departments can restrain the outbreak. “Every single country has the possibility to contain [transmission],” she said. “I’m not suggesting that this is easy. … But it can be controlled.”
Helen Branswell contributed reporting.