In coronavirus testing, false positives are more hazardous than they might seem.

In the high-stakes world of coronavirus testing, false positives are widely considered to be benign in comparison with false negatives, which can deprive infected people of treatment and embolden them to mingle with others, hastening the spread of disease.

But false positives, which incorrectly identify a healthy person as infected by the virus, can have serious consequences as well, especially in places where the virus is scarce.

False positives are generally very rare among tests that have been vetted by the Food and Drug Administration. But any test can be plagued by contamination, mishandling or technical glitches, leading a device to spot the coronavirus where it is not.

In places where the virus is relatively scarce, false positives may even outnumber accurate positives — eroding trust in tests and, under some circumstances, prompting outbreaks of their own.

Adverse effects include:   ...