Ketchup, squash and fruit do not deliver positive Covid-19 results

29 June 2021
What was claimed

Ketchup, orange squash, tomatoes, strawberries and grapes all deliver positive Covid-19 lateral flow test results.

Our verdict

We know that foods high in acid can break lateral flow tests and cause it to appear “positive”. However, research has shown that they very rarely deliver a false positive result when used properly, on people.

A Facebook post suggests that a number of foods and drinks can deliver a “positive” Covid-19 result on a lateral flow test.

This is true, insofar as the acidity in some foods can break a test and cause a second line to appear, as if the test were positive. This doesn’t mean that the foods contain the Covid virus, however, or that the tests are unreliable when used correctly on people. 

The photo shows what appear to be a citrus fruit, a tomato, a grape, a strawberry, a bottle of Kia Ora squash, a bottle of Tesco orange squash and a bottle of Heinz tomato ketchup, each one beside a completed lateral flow test.

A caption says “my cousin done this and all of them are positive apart from a grapefruit.”

A positive result creates two lines next to the areas marked “C” and “T” on the lateral flow test. Any other result is either negative or invalid.

It is not easy to tell from the photo whether all the tests do have two lines, but even if they do, this doesn’t mean that the tests are not reliable for their intended purpose.

Lateral flow tests are very unlikely to give a false positive result if used correctly. However, we have checked claims in the past about how samples from a kiwi fruit, Coca-Cola and oranges have incorrectly created “positive” results.

This article is part of our work fact checking potentially false pictures, videos and stories on Facebook. You can read more about this—and find out how to report Facebook content—here. For the purposes of that scheme, we’ve rated this claim as missing context because using lateral flow tests on acidic foods can break them, causing a second line to appear. Research shows lateral flow tests rarely return false positive results when used correctly.

Full Fact fights bad information

Bad information ruins lives. It promotes hate, damages people’s health, and hurts democracy. You deserve better.