Weather data could help predict up to three days in advance when the number of out-of-hospital cardiac arrests (OHCA) is likely to rise above average, according to a nationwide study of more than 114,000 cases by researchers from Semmelweis University, the Budapest University of Technology and Economics, and the Hungarian National Ambulance Service. Published in Public Health, the study found that lower temperatures were among the most important weather-related risk factors.

Researchers compared out-of-hospital cardiac arrests recorded between November 2018 and December 2023 with daily meteorological indicators, including temperature, wind speed, atmospheric pressure, humidity and air quality. Their goal was not only to identify weather conditions associated with cardiac arrest, but also to determine whether these factors could be used to predict periods when case numbers would rise above average.

Out-of-hospital cardiac arrest is a major cause of death in developed countries. In Europe, an estimated 67–170 cases occur per 100,000 people each year, while survival remains below 10%. Being able to anticipate increases in cases could help emergency medical services and hospitals prepare for higher demand, while raising public awareness about the importance of rapid intervention and resuscitation.

Temperature emerged as a particularly important factor. Every 1°C decrease in average temperature was associated with a 1.4% increase in the daily number of out-of-hospital cardiac arrests. Nearly 18% more events occurred in winter than in summer, suggesting that lower temperatures generally—not only extreme cold—may increase risk. A daily temperature drop of more than 5°C could also provide a useful warning signal.

Importantly, the effects of weather changes were not always immediate. Cardiac arrest numbers could increase up to three days after certain weather conditions, creating an opportunity for early warning systems to forecast periods of increased healthcare demand.

“In a previous study, we examined how extreme cold and heat affect the incidence of out-of-hospital cardiac arrest. This time, we went one step further and investigated whether weather patterns could be used to predict when higher-than-average numbers of cases are likely to occur,” said Dr. Endre Zima, Professor at Semmelweis University’s Heart and Vascular Center and lead researcher.

The researchers developed a predictive model combining meteorological and ambulance service data. According to first author Dr. Ádám Pál-Jakab, the model could identify one to three days in advance when nationwide cardiac arrest numbers were likely to exceed average levels. Importantly, the model predicts population-level case numbers rather than a person’s risk.

The findings could eventually support an early warning system using weather forecasts to help ambulance services and hospitals plan staffing and capacity. Such systems might also alert people with cardiovascular disease and their families to higher-risk periods, encouraging greater attention to warning symptoms and earlier medical care when necessary.

More information: Ádám Pál-Jakab et al, Meteorological associations with out-of-hospital cardiac arrest: A national population-based time-series analysis, Public Health. DOI: 10.1016/j.puhe.2026.106145

Journal information: Public Health Provided by Semmelweis University