NEW YORK (CBSNewYork) – There’s a health alert involving avocados.

The Food and Drug Administration is warning people to thoroughly wash the outside skin of every avocado, even though we just eat the inside.

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WEB EXTRA: FDA’s Avocado Safety Report (.pdf)

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It turns out one in five avocados tested positive for a bacteria that can cause listeria.

The two year study from 2014-2016 includes both the domestic and imported kinds of avocados.

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Listeria symptoms are flu-like, and include muscle aches, fever and vomiting.