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Excess Out-Of-Hospital Mortality and Declining Oxygen Saturation Documented by EMS During the COVID-19 Crisis in Tijuana, Mexico

By Joseph Friedman, Alheli Calderon-Villarreal, Ietza Bojorquez, Carlos Vera Hernandez, David Schriger, Eva Tovar Hirashima

Posted 18 May 2020
medRxiv DOI: 10.1101/2020.05.13.20098186

Objective: Emergency medical services (EMS) may serve as a key source of rapid data about the evolving health of COVID-19 affected populations. A study in Italy reported that EMS-documented out-of-hospital cardiac arrest rose by 58% during the peak-epidemic. EMS and hospital reports from several countries have suggested that silent hypoxemia-low oxygen saturation (SpO2) in the absence of dyspnea-is associated with COVID-19 outbreaks. It is unclear, however, how these phenomena can be generalized to low-and-middle-income countries (LMICs). Tijuana is a city on the Mexico-United States border that may serve as a bellwether for cities in other LMICs. Using EMS data, we assess changes in out-of-hospital mortality and the SpO2 of respiratory patients during the COVID-19 period. Methods: We calculated numbers of weekly out-of-hospital deaths and respiratory cases seen by EMS in Tijuana, and estimate the difference between peak-epidemic rates and forecasted 2014-2019 trends. Results were compared with official COVID-19 statistics, stratified by neighborhood socioeconomic status (SES), and examined for changing demographic or clinical features, including mean (SpO2). Results: An estimated 194.7 (95%CI: 135.5-253.9) excess out-of-hospital deaths events occurred during April 14th-May 11th, representing an increase of 145% (70%-338%) compared to forecasted trends. During the same window, only 8 COVID-19-positive, out-of-hospital deaths were reported in official statistics. This corresponded with a rise in respiratory cases of 274% (119%-1142%), and a drop in mean SpO2 to 77.7%, from 90.2% at baseline. Peak respiratory cases were concentrated in high-SES neighborhoods, while the highest out-of-hospital death rates were observed in low-SES areas. Conclusions: EMS systems may play an important sentinel role in monitoring excess out-of-hospital mortality and other trends during the COVID-19 crisis in LMICs. Using EMS data, we observed increases in out-of-hospital deaths in Tijuana that were nearly threefold greater magnitude than increases reported in Italy. Furthermore, these deaths may be missing from official records describing COVID-19 patients. We also found evidence of worsening hypoxemia among respiratory patients seen by EMS, suggesting a rise in silent hypoxemia, which should be met with increased detection and clinical management efforts. Finally, we observed that social disparities in out-of-hospital death that warrant monitoring and amelioration.

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