The Ruby Princess cruise ship. (Image: AAP/Dean Lewins)

Luxury cruise ships the Ruby Princess, the Diamond Princess, the Grand Princess and the Costa Luminosa have a few things in common: for one, they are all owned by US giant Carnival Cruises; and they have all carried COVID-19 infected passengers.

In February, in one of the world's first large outbreaks of coronavirus, the Diamond Princess remained moored in waters off Japan with hundreds of infected passengers on board. 

In March, nearly 2000 passengers had to be quarantined on US military bases after infected passengers were found on the Grand Princess.