We Still Need to Go Backwards on Contract Tracing

Last November, some asshole with a blog noted this about the absence of backwards contract tracing in D.C.:

Regular followers of my cataloging the COVID-19 statistics for D.C. will know that I routinely argue that we still don’t understand the specifics of COVID-19 transmission in D.C…

In other words, D.C.’s contact tracing isn’t finding these superspreader events. For example, consider this example of an adult who infected multiple family members at a child’s birthday party…

The real question isn’t what happened within the family–that’s obvious. These also are the cases that are easy for D.C. to detect because the focus is on close contacts, not deep investigation. What we need to ask is how the person who brought COVID-19 to the party (literally) contracted it in the first place. Was it work? Dining out with friends? Because the good news, if it can be called that, is that we typically don’t have to go too many links back to find the superspreading event. Once we understand those, we can make better policy.

But until we reallocate some of our resources to really understanding how spread occurs, we’re left with broad brush generalities–which means our responses have to be broad too, even if not truly necessary. That leads to a political problem, since the city (and in fairness, no other states too) doesn’t want to have broad rollbacks. But broad rollbacks are the only policy option right now–or letting people get seriously sickened or die, since we don’t have the evidence to put any other policy options* on the table.

We need to move backwards.

Cue William Hanage and K.J. Seung about the Provincetown, MA outbreak (boldface mine):

What happened next is instructive. Noticing an uptick in cases, investigators in Massachusetts tried to identify clusters of transmission and where they happened. Where you find one transmission event, you are likely to find more. This approach is called “source investigation,” or “backward contact tracing.” When a case is reported, investigators look back at a person’s activities to identify where they might have been infected, and then determine whether others may have been infected at the same time. The technique has proved useful for analyzing disease clusters in countries like Australia and New Zealand, where every case of unknown origin is considered an emergency because it could mean that a potential superspreading event has not been found.

…But contact tracing protocols in many states are not well suited for superspreader outbreaks outside of those controlled settings, because they often focus on who the case might have infected, not on the location where the infection occurred. Patrons at restaurants and bars are largely anonymous; each person typically knows only a handful of others.

Source investigation complements standard contact tracing; it’s not a substitute. When outbreaks are detected, people need to be informed immediately, so they can get tested and ensure they are not unknowingly spreading the virus. Once a cluster is detected, venues should re-evaluate their Covid mitigation measures and ensure that staff are vaccinated and ventilation systems refresh indoor air at least four to six times per hour. High-risk venues should keep lists of patrons, and outreach to customers through social media can be very effective. Mandating that customers are vaccinated, as New York, San Francisco and New Orleans have done, may not suffice to prevent outbreaks. Some European countries are requiring evidence of a negative coronavirus test for unvaccinated people entering indoor entertainment venues….

The tools and techniques that the Massachusetts Department of Public Health used in Provincetown are not special and should be used much more widely. All over the country, large groups are gathering, often in poorly ventilated spaces. Nightclubs and bars are packed in many cities, and most have much lower vaccination rates than Provincetown. Just because we are not looking for outbreaks in these locations does not mean that they are not happening. Are Florida’s rocketing hospitalizations being driven by myriad little Provincetowns? Are contact tracers looking?

…While vaccination is the single most effective tool we have to fight Delta, it does not reduce transmission to zero. So we must also employ other weapons in our arsenal: source investigation, masks indoors when cases are surging and readily available testing. Our pandemic future may remain unwritten, but fatalism in the face of Delta will only lead to yet more unnecessary illness and death.

It has been months, and our policy makers still haven’t learned from experience. In Florida’s case, it doesn’t help that the governor is a Great Barrington Declaration ideologue, but it’s not like D.C., a Democratic stronghold, is kicking ass on backwards contract tracing either–which is why I regularly argue most elected officials, based on their pandemic response, shouldn’t be returned to office*.

Given that most public officials are still in the ‘vaccinate and pray’ mode, even as they (other than New York City’s DeBlasio) don’t go hard on vaccination requirements, I don’t see policy makers listening to either Hanage’s and Seung’s (or my) advice.

Anger is the appropriate emotion.

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