Contact tracing has long been used to combat the spread of sexually transmitted diseases like syphilis in the 1930s, and HIV in the 1980s. But the practice has raised privacy concerns.

Contract tracing was a crucial public health tool in stopping the spread of the deadly Ebola virus in 2014. Over 150 people who came into contact with Ebola victim Thomas Duncan in Texas were tracked and monitored. Above, a contact tracer in Sierra Leone spoke to the family of an Ebola victim.

A year ago, public health workers contacted people who had been exposed to measles, a nearly-eradicated disease that has been gaining an occasional foothold among those who aren’t vaccinated against the virus.

Now with the coronavirus, contact tracing is going digital. Apple and Google are creating phone software that will alert users who have been near someone who has tested positive for the virus.

Other countries have used surveillance systems to track infections among citizens. Israel and Singapore have used cellphone geolocation data; South Korea has monitored credit card transactions and closed-circuit video footage.

There are potential pitfalls for privacy and accuracy. In South Korea, government surveillance data revealed enough information about a woman with Covid-19 that she was identified and harassed online. A woman in Israel was quarantined after merely waving to an infected person from outside his apartment.

“Exposure notification” apps using phone data are being tested in the United States as concerns grow about what personal information will be gathered and how it will be used and stored. States are hiring thousands of workers to do person-to-person outreach to anyone exposed to the virus.

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