35 days at sea and still testing positive?

Argentinian health officials are scrambling to understand how nearly every crew member of a ship which spent 35 days at sea were found to have contracted coronavirus upon returning to land.

All 61 sailors aboard the trawler, Echizen Maru, tested negative for the virus upon departure from Buenos Aires in late May.

They were then flown to the Ushuaia, a typical jumping-off point for Antarctic voyages nicknamed “the end of the world”, where they were quarantined in a hotel for two weeks before setting sail... More here.

The kind of story that sends a shiver until you think about it. Presumably one of them already had Covid and it was a slow burner or one of the surfaces was infected on the ship just before they left. Or, I don't want to think about any other possibility.