The incidence of tropical sprue among North Americans living temporarily in Puerto Rico was found to be approximately 8% annually. Preliminary surveys of returnees from certain parts of Southeast Asia suggest that the incidence may be even higher in that part of the world.
Sheehy TW, Cohen WC, Wallace DK, Legters LJ. Tropical Sprue in North Americans. JAMA. 1965;194(10):1069-1076. doi:10.1001/jama.1965.03090230037009