If you look at this distribution map from the CDC (https://www.cdc.gov/malaria/about/distribution.html https://www.cdc.gov/malaria/about/distribution.html) you

If you look at this distribution map from the CDC (https://www.cdc.gov/malaria/about/distribution.html https://www.cdc.gov/malaria/about/distribution.html) you can see that Mexico and Central America as well most of South America are in yellow with malaria known to occur in some places and the US, Canada, and Europe with Malaria not known to occur in blue, I think my question is valid. How many of the 80 million legal visitors are from Africa and SE Asia or yellow or orange areas? I lived in Macau for 7 years and Indonesia for a year and spent a lot of time in remote areas with dengue fever and malaria present, and even with a non-stop flight you are 16 hours from JFK from Hong Kong not including the 2 hours at the airport and the travel to the airport. In the past few years there are now increasing numbers of Venezuelan, Cuban, and Haitian immigrants (small orange area is Haiti on CDC map) and people from Ukraine, India, and Turkey. My guess is your healthcare is not on par with those flying in legally (look at the blue areas from overseas) too, so I don't think this is an unreasonable factor to consider especially since illegal immigration is not as easy to track or control given you only count who you catch and some statistical estimates based on that sample.