After three people died on a cruise ship struck by a hantavirus, authorities are actively tracking down 29 people who had left the ship. They’re trying to trace the spread of the virus. It’s a long, arduous, global process to find and notify people who might be at risk of infection.

Hey, wasn’t there supposed to be an app for that?

Contact-tracing apps were a global effort starting in 2020 during the Covid-19 pandemic. Enabled by phone companies like Apple and Google, contact tracing was designed to use Bluetooth connections to detect when people had come in contact with someone who had or would later test positive for Covid and report as much. It didn’t do much to solve the spread of the pandemic, but tracking the virus became more effective at least. The same process wouldn’t go well for the hantavirus problem.

“There is no use of apps for this hantavirus outbreak,” Emily Gurley, an epidemiologist at Johns Hopkins University, wrote in an email response to WIRED. “The number of cases are small, and it’s important to trace all contacts exactly to stop transmission.”

On a smaller scale of infection like this, officials have to start at the source (an infected individual), then go person-by-person, confirming where they went and who they might have come into contact with. Data collected by apps from a broad swath of devices would not be anywhere close to accurate enough to give a good idea of where the virus might have hitchhiked to next.

Contact tracing on a wider scale, like, say, a global pandemic, is less about tracking the individual infections and more about understanding what parts of the population might be affected, giving people the opportunity to self-quarantine after exposure. But that depends on how people choose to respond, and how the technology is utilized by public emergency systems. During the Covid pandemic, contact-tracing via apps tended to work better in more carefully managed European countries, but did not slow the spread in the US.

Making devices accessible to that kind of proximity information has also brought all sorts of concerns about privacy, given that the technology would require always-on access to work properly. Contact tracing also struggled to maintain accuracy, and in some cases could be providing false negatives or positives that don’t help further real information about the spread of the virus.

Especially in the case of something like the Hantavirus, where every person on that cruise ship can theoretically be directly tracked and contacted, it’s better to do that process the hard way.

“During small but highly fatal outbreaks, more precision is required,” Gurley wrote.