Hot and Crowded: Temperature, Healthcare Utilization and Patient Outcomes

Extreme heat raises emergency demand and may increase mortality through hospital congestion when shocks hit many people at once. Using administrative records from Mexico’s largest public health system, we separate direct heat effects from congestion spillovers. Days with maximum temperature above 34°C increase ED visits by 6.9 percent and hospitalizations by 4.2 percent, with sicker ED patients discharged home more often. In-hospital deaths rise for already-admitted patients, suggesting important spillover effects, and deaths disproportionately increase outside hospitals. These results identify health-system capacity as an important margin of adaptation to extreme heat.