All of these factors were in play in northeastern Brazil cities where the first clusters of microcephaly cases were noted, as they were in Colombia, the second major Latin American country to be affected. From there we can predict where the virus will strike next. High concentrations of the A aegypti mosquito, crowding, and poverty converge in the Central American countries of El Salvador, Guatemala, Honduras, and Nicaragua; parts of Mexico such as the Mayan villages in Yucatan; and in the Caribbean nation of Haiti, where owing to its depleted health system we can expect a humanitarian catastrophe to unfold. Poor areas of Puerto Rico will be affected, as will urban centers of the continental United States where A aegypti numbers are their highest and poverty is at its worst. Those factors combine mostly in poor neighborhoods of major Gulf Coast cities such as Houston and Galveston, Texas, and New Orleans, Louisiana, as well as Florida16 (Figure). With a combined population of approximately 60 million individuals, more than 1 million pregnancies could be at risk in US Gulf Coast states.