# Influence of extreme temperatures on out-of-hospital cardiac arrest cases in Hungary: a national time-series analysis

## TL;DR

Extreme cold and heat in Hungary are linked to increased out-of-hospital cardiac arrests, with cold effects lasting longer than heat effects.

## Contribution

This study identifies prolonged extreme temperatures as independent cardiovascular risks with distinct temporal patterns.

## Key findings

- Sustained cold spells increased OHCA risk with delayed and persistent effects lasting over 14 days.
- Heatwaves caused acute, short-term OHCA risk peaking within 2–4 days.
- Minimum OHCA risk occurred at 19.0°C with a U-shaped temperature-risk relationship.

## Abstract

Out-of-hospital cardiac arrest (OHCA) represents a critical public health challenge, with poor survival. Our objective was to evaluate the association between extreme temperature events and OHCA incidence in Hungary, and to assess the potential influence of additional meteorological factors, including humidity and solar radiation.

We conducted a national time-series analysis of 116,579 adult OHCA cases from November 1, 2018, to December 31, 2023. Using negative binomial regression with cluster-robust standard errors, we estimated associations between daily OHCA counts and extreme temperature events, controlling for day-of-week, seasonality, and long-term trends. “Added-effect” models isolated risk attributable to sustained events while controlling for underlying non-linear temperature-health relationships through natural cubic splines. Distributed lag non-linear models (DLNM) characterized exposure-lag-response patterns over 21 days.

The temperature-OHCA relationship exhibited a characteristic U-shape with minimum risk at 19.0 °C. Sustained cold spells (≥2 days with daily minimum temperature ≤−9.2 °C, 2nd percentile) were associated with the highest risk increase (IRR 1.189; 95 % CI: 1.089–1.299; p < 0.001). Sustained heatwaves (≥3 days with daily average temperature ≥27.1 °C, 95th percentile) also significantly increased risk (IRR 1.110; 95 % CI: 1.032–1.195; p = 0.005). Single severe cold days (minimum temperature <−10 °C) carried an IRR of 1.143 (95 % CI: 1.012–1.291; p = 0.031). DLNM analysis revealed distinct temporal patterns: heat effects were acute and transient (peak at days 2–4, resolved by day 7), while cold effects were delayed and persistent (emerging at day 3, sustained beyond 14 days).

Prolonged extreme temperatures represent independent cardiovascular hazards beyond isolated daily exposures. The immediate impact of heat and the delayed, persistent effect of cold carry important implications for public health preparedness, emergency service planning, and the timing of clinical advisories.