One hot day last summer, Clarisa Lugo was inspecting and counting corn and soybean plants in the middle of a 300-acre farm field in Illinois when she started throwing up and panting. Her heart raced, she stopped sweating and a pounding headache didn’t go away for hours.

The heat index — a blend of temperature and humidity — had hit 105 F (40.56 C), and Lugo, who was eight months pregnant, was suffering from heat illness.

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