Real-time heat-related illness

Extreme heat is dangerous. It can cause illness, make chronic conditions worse, and even kill. Heat-related illnesses happen when the body cannot cool down enough, and include heat exhaustion, muscle cramps, fainting and heat stroke, the most serious form of heat-related illness. Heat can exacerbate chronic conditions, such as cardiovascular diseases or kidney conditions, that may not be recognized or labeled as heat-related.

The weather forecast is the best way to predict heat-related health outcomes. We can also track heat-related illness with near real-time electronic data from emergency departments at hospitals throughout NYC. These data include illnesses directly attributed to heat, not the full burden of heat-related health impacts.

These data provide a useful indicator of the health impacts of extreme heat. Typically, 10,000 people visit an emergency department (or ED, also called the emergency room) every day in NYC. When somebody visits the ED, they're examined, and asked to describe how they feel. These findings are recorded, and hospitals send these records to the Health Department. We search these records for diagnostic codes (when available) and words describing why patients are at the ED to track specific health conditions in near real-time. This is called syndromic surveillance, and it helps us track citywide trends.

Below are data on the number of heat syndrome visits to emergency departments, and the daily maximum temperature. What do we use these data for?


In NYC, an extreme heat event is two or more days with a heat index reaching 95 °F, or one or more days reaching 100 °F.

To learn more about heat and health, visit Extreme Heat and Health. To stay safe in the heat, visit Beat the Heat.

Daily data (2022)

Max daily temperature is the heat index or temperature, whichever is higher, as recorded by the National Weather Service weather station at La Guardia Airport.

Data from 2017 to 2021