Whether contact tracing is referred to as a tool, a strategy, a method or a measure makes no difference; public health officials agree it’s a process with the goal of identifying, tracking, tracing, and, ideally, ending a communicable disease’s chain of transmission.
But its success depends on a number of factors, including testing for the disease and participation.
Local and state health departments have employed contact tracing for decades but have never faced a virus like SARS-CoV-2, or the disease it causes, Covid-19. It is truly unprecedented, according to numerous public health experts and officials.
Contact tracing is considered a tool for "containment" of disease spread and is different from the most recently and widely used tool for "mitigation," the now-expired statewide stay at home order.
With the order now lifted the Pima County Health Department is preparing to increase contact tracing in the coming weeks, according to its new director, Dr. Theresa Cullen.
It's in the process of hiring 127 contact tracing investigators.
How it works
The way contact tracing works is fairly straightforward; whether it is effective is another matter.
“It really starts with that positive test result,” Dr. Crystal Watson, an assistant professor at the Bloomberg School of Public Health at Johns Hopkins University, said during an online livestream panel on contact tracing May 28.
“You take that test and then you take the next step which is to notify the person that they are positive, [then] a health official will reach out to them to see how they are doing, how their illness is progressing, offer them resources and connections to healthcare if they need it, but then also ask who they’ve been around during the time that they have been infectious,” Watson said.
The most recent CDC guidance suggests contact tracing investigators, or contact tracers, gather the names and numbers of contacts a Covid-19 patient may have made in the preceding two days since the onset of symptoms. PCHD will seek contacts made from two days before the viral test was administered, according to Cullen.
A contact is considered someone an infected person, or a "case," has been within six feet of for a duration of at least 15 minutes.
“[This] allows public health to notify those contacts that they may have been exposed and ask them to stay at home and self-quarantine for 14 days, and if those contacts are indeed infected and they are quarantined, the hope is that they are not infecting others and we can stop chains of transmission there,” Watson said.
When an investigator informs a contact they may have been exposed to the virus, they do not share the personal information of the infected individual for privacy reasons and, ideally, links the contact with resources they may need to effectively quarantine.
As contacts self-quarantine, they are asked to monitor their symptoms and regularly report them to case investigators.
The Arizona Department of Health Services is piloting a 14-day monitoring and reporting system in two counties for contacts to report symptoms during quarantine via phone, text or online. ADHS would not indicate whether Pima County is participating in the pilot.
In the event a contact turns out to be infected after getting tested themselves, an investigation may then begin into any contacts they made. This is known as second-order tracing, but this is likely determined based on the approach of the local health agency.
Eric D. Perakslis, a data scientist and Rubenstein Fellow at Duke University, told the Green Valley News that there are multiple ways to approach contact tracing but anyone experienced in it will likely take a targeted approach.
“I do believe contact tracing that’s done right can be an intervention that saves lives. Which is a further reason to do it in a targeted fashion.
“If I’m just doing everybody with no discretion at all, I’m not looking out for people that are at extra risk for disease. I’m not looking out, for instance, for people that may be the guy on the list who happens to be a UPS driver who might be a super-spreader," Perakslis said.
“People that have been doing this a long time learned to do it primarily in low-resource settings. For me it was 2014 and Ebola in West Africa.
“We didn’t have all the testing that we needed and it took days to get a test result back, and so you actually figure out ways to do it in a targeted way very, very quickly," Perakslis said.
“You can target it based on what the priorities or limitations are in your system.”
Testing informs tracing
An important part of successful contact tracing is widespread virus testing, according to Dr. Jennifer Nuzzo, an associate professor from Bloomberg School of Public Health.
“Tests can tell us who is infected and capable of transmitting their infections to others, even if they don’t have symptoms or are just early in their course of illness,” Nuzzo said during a recent panel on contact tracing.
Nuzzo said there is a range of metrics to assess whether testing is adequate, but “testing positivity” is one of the most important.
Testing positivity refers to the percentage of positive viral PCR tests out of all that have been administered.
Nuzzo said ideally it should be a small number. If the number is high then it is likely not enough people are being tested, that only the sickest of the sick, those we are otherwise sure are infected, are being tested.
“We want to make sure we’re casting a wide enough net to make sure we are finding as many Covid cases as possible,” Nuzzo said.
The county’s current testing strategy prioritizes those most vulnerable to being infected by the virus including senior citizens living in congregate care settings such as skilled nursing facilities and nursing homes, and the staff taking care of them.
The county aims to test the estimated 18,000 individuals who make up this group, having tested about 8,000 so far, but its testing stockpile sat at around 5,500 as of May 29, according to a department spokesperson.
The World Health Organization recommends that testing positivity be "less than five percent" in a given population for 14 consecutive days before considering lifting mitigation restrictions like stay at home orders.
The Johns Hopkins Covid-19 Testing Insights Initiative tracks testing positivity and indicates Arizona’s rate has not reached the suggested less than five percent threshold since the start of the pandemic. Two weeks ago Arizona was at 9.6% testing positivity and has since risen to 14.3%, according to the initiative’s website.
“ADHS is monitoring the percent positivity for COVID-19 testing being performed, as this is a valuable metric in assessing the current status of the pandemic in Arizona,” Holly Poynter, a public information officer at ADHS said in an emailed response to questions.
“Throughout the COVID-19 response, ADHS has been working with partner laboratories in order to increase access to testing for Arizonans.
“Testing Blitzes were held on the weekends through May. This has supported a dramatic increase in COVID-19 testing in Arizona,” Poynter said.
“If you’ve got 50 tests today, use them smartly,” Perakslis said.
“This ‘we’re going to test everyone, we’re going to trace everyone approach’ isn’t always realistic. In an ideal world with lots of money and infinite resources and time, fine. The reality is that people that know how to do this well learned how to do it without those luxuries. And figured out how to do it very very quickly, you know, how to think about this.”
Another aspect of testing that may influence the effectiveness of contact tracing is how long it takes to get a test result from the lab.
County Administrator Chuck Huckelberry pointed out in a May 29 memo that it took nine days for a “high-ranking member of county management” to get a test result, which is an “example of either a failed, or an overwhelmed system.”
“We indicated one of the pitfalls associated with successful contact tracing was the timely receipt of active viral PCR test results,” the memo said. “Ideally, these results would be provided within 24 hours of the test, but no later than 48 hours in order to be effective in assisting...contact tracing.”
A memo Huckelberry released Friday said the county "continues to emphasize the use of Paradigm Laboratories," which has been able to meet the desired time frame.
Pick up the phone
Another crucial factor in the success of contact tracing is participation by those who’ve tested positive for the virus and any contacts they provide to the contact tracer.
“Contacts are critical, it’s how we believe we can change the epidemic,” Cullen said in a recent health update.
“This might be for many of you the first contact you’ve had with PCHD, trust me, we’ll try to make it informative for you. The important thing for us is we need you to pick up the phone.
“If we contact you it means we have educational materials for you, we want to share with you information we know about the Covid-19 infection,” Cullen said.
“The effectiveness of contact tracing, culturally, is really tied to community. The most effective programs I’ve seen have been community-run,” Perakslis said.
In his experience, trust is an important part of the tracing process and having tracers that reflect the community helps to develop it.
Will ramped up efforts to track and contain the virus through contact tracing at the local level be successful? If anything it’ll be interesting according to Perakslis.
“I think the fact that we have a lot of people running around collecting a lot of data, you know you went from having zero contact tracers to [a] state hiring 500 people that have never done it before and it’s being managed by 50 people who have never done it before.
“I expect we’re going to see some really interesting things going on with all of this being scaled up at once,” he said.