Over the past few months, a number of Japanese health officials have praised their country’s contact tracing approach, saying it’s one of the “secrets” to their early success in containing COVID-19.
“Most other countries adopted what we call prospective tracing,” Shigeru Omi, chair of an expert panel advising the Japanese government on COVID-19, told the Financial Times in June. Instead, Japan has focused on something dubbed "retrospective contact tracing," which Omi said has allowed them to pinpoint major sources of infection.
Contact tracing typically starts with a known case and looks forward, asking, ‘Who else might the infected person have passed the virus to once they became infectious?’ This focus centers on identifying future cases. But in Japan, contact tracers have also made a habit of looking backward, asking, ‘Where did the initial case pick up the virus in the first place? And who else might have gotten it from the same person, location, or activity?’
In July, Yasutoshi Nishimura, Japan’s minister of state for economic revitalization, wrote that a "core insight" about COVID-19 led them to retrospective contact tracing.
“Early on, our health experts noticed that the disease spreads in a peculiar way. Although the coronavirus is highly contagious, it is not uniformly contagious. Most who are infected by it—about 80%—never pass it on to anyone else. The bulk of infections can be traced to a small number of ‘super-spreading events," Nishimura wrote. "Because COVID-19 is a disease that spreads along relatively small numbers of super-spreading transmission chains, if you can isolate these chains or prevent them from forming, transmission of the virus isn’t sustainable.”
Retrospective contact tracing is not a new concept, according to Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security.
“This is something that has a history in infectious disease epidemiology and it’s much more emphasized for chronic infectious diseases,” said Adalja. “Think of Typhoid Mary, for example. Looking back retrospectively may bring you back to a common source.”
It’s unclear to what extent contact tracers in the U.S. are following this more comprehensive approach. Contact tracing efforts are largely handled at the local level, and their approaches and resources vary widely.
Tair Kiphibane, who leads the contact tracing efforts in Salt Lake County, Utah, said in an email that doing both prospective and retrospective contact tracing “is ideal and the gold standard.” But, she wrote, “It takes a lot of manpower and resources to contract trace retrospectively. We had attempted this in the past, but it was too burdensome for the contact tracers and this was not a sustainable approach.”
Josh Michaud, an infectious disease epidemiologist by training who studies global health policy with the Kaiser Family Foundation, suspects Salt Lake County is not alone.
“Many public health departments and contact tracing efforts in particular are understaffed, under-resourced and under-prioritized so they have to pick and choose their battles,” said Michaud. “They’re also facing, across much of the U.S., high transmission levels, which is not the case in Japan. And it’s true: Retrospective contact tracing adds another layer of complexity and requires a little bit more legwork.”
Data isn’t available to quantify to what extent Japan’s contact tracing has interrupted chains of COVID-19 transmission there, Michaud added. But several modeling studies — still in draft form — from groups at the London School of Hygiene & Tropical Medicine, MIT and others show the potential benefits of looking backwards, if resources allow. (As Asia Times has described, Japan was already somewhat prepared for the heavy lift of retrospective contact tracing because they'd used it to quell recent outbreaks of tuberculosis).
“From the modeling results, it’s clear that when you combine the two you’re likely to be more effective than just doing the regular prospective contact tracing,” said Michaud.
Investing resources on the contact-tracing side could potentially help save resources on the other end of a COVID-19 response. As Amesh Adalja pointed out, a heavier emphasis on retrospective contact tracing could suss out exactly which activities are responsible for the most spread, allowing local health officials to focus their energies there rather than instituting heavy-handed lockdowns.
“So if it is bars, if it is waterparks, if it is hair salons, whatever it might be -- that's going to help you direct limited public health resources in a targeted manner to stop transmission,” he said. “If you can direct public health actions towards those high risk activities, you can leave the rest of the people alone to go about their lives. And I think that's what we want to get to, is precision-guided public health. The information gleaned from contact tracing both prospective and retrospective helps health departments do that.”
However, Adalja pointed out that mistrust of public health officials could continue to hamper contact tracing efforts, regardless of which approach they take.
“We know in many parts of the country,” he said, “people are not picking up the phone when the health department calls.”
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.