COVID-19 epidemic in the Seine-Saint-Denis Department of Greater Paris: one month and three waves for a tsunami

Abstract

Introduction 

Worldwide, the COVID-19 epidemic has put health systems to the test. The excess mortality is partly due to the influx of patients requiring hospitalization and intensive care. We propose that the chronology of epidemic spread gives a window of time in which hospitals can act to prevent reaching capacity.

Methods 

The out-of-hospital SAMU Emergency Medical System in an entry point into the French health care system. We recorded the number of patients managed, of patients transferred to emergency departments (ED), and of mobile intensive care units (MICUs) dispatched. Each criterion was compared to the mean of the same criterion over the previous 5 years. The alert threshold which indicated a public health crisis was defined as a 20% increase compared to the 5-year mean.

Results 

The reference period, from January 2015 to December 2019, included 3 381 611 calls, and 1 137 856 patients. The study period, from 17 February to 28 March 2020, included 166 888 calls, and 56 708 patients. The daily numbers of patients managed crossed the threshold on February 25, and increased until the end of the study period. The daily number of patients transferred to ED crossed the threshold on March 16, and increased until the end of the period. The daily number of MICUs dispatched crossed the threshold on March 15, and increased until the end of the period.

Conclusion 

The COVID-19 epidemic reached our department in three consecutive waves which overwhelmed the health care system. The first wave preceded by 30 days the massive arrival of critical patients. Health care systems must take advantage of this delay to prepare for the third wave.

Introduction

Having migrated from China a couple of months ago, the COVID-19 wave has reached Europe and continues to spread throughout the world [^1,2]. The epicenter moved progressively from China to Europe, then from Europe to the USA [^3–5]. The death toll is already catastrophic, with over 90 000 deaths worldwide reported to date. In every nation affected (185 countries have reported cases as of April 22), health systems have been put to the test [⁶]. The excess mortality associated with COVID-19 is partly due to inadequate medical resources, in particular human or material resources in intensive care units (ICUs), and other needs related to the treatment of severe forms of the disease [^5,7,8]. This phenomenon is caused by the influx of patients, and is exacerbated by the exponential growth in the number of critical patients requiring hospitalization and intensive care [^9,10]. We analyzed the evolution of the COVID-19 epidemic and the chronology of its spread in the Seine-Saint-Denis Department of the Greater Paris region in order to evaluate the ways in which we could have prevented hospitals from reaching admissions capacity in ICUs and other departments. Our goal was to determine the lapse of time between the first signs of pressure on the emergency medical system and the influx of critical patients in the hospitals.

Methods

EMS organization

The French health care system is based on a multi-level organizational model, beginning outside the hospital. Patients requiring urgent care may dial ‘15’, a single, nationwide, toll-free telephone number [¹¹]. The number is for the Service d’Aide Médicale Urgente (SAMU, or Emergency Medical Service). Callers are then put in contact with a doctor who, after a clinical interview conducted over the phone, decides on the type of care to be given. This may include medical advice, hospital transfer by a non-emergency transport ambulance, dispatch of a rescue vehicle (generally operated by the fire department) or of a general practitioner to the patient’s home or, in severe cases and/or when rapid prehospital care is required, a mobile ICU (MICU), with an emergency physician, nurse, and specialized paramedic on board. In contrast to the 911 system in the USA, the SAMU is specific to medical care. The Fire and the Police Departments are not part of the same system and cannot be reached directly by dialing ‘15’. We have previously shown that an increase in calls received by the SAMU EMS is a sensitive marker of a public health crisis. An increase of over 20% in the number of patients managed has been defined as the alert threshold during an influenza pandemic or during a heat wave; inversely, a decrease of over 20% was observed during major media events such as televised soccer games [^12,13].

Early on in the unfolding of the epidemic, beginning in the month of January, health authorities encouraged patients to call this number in the event that they displayed COVID-19 symptoms, as well as to obtain medical information and advice.

Site

Seine-Saint-Denis is a French department bordering Paris to the northeast, and part of Greater Paris. It is an urban area of approximately 1.6 million inhabitants over an area of 236 km², making it one of the most densely populated regions in France. The population is particularly disadvantaged socioeconomically. In 2019, the SAMU – Emergency Medical Service received 684 000 emergency calls, corresponding to 237 791 patients managed.

Criteria

We studied the number of patients managed in the SAMU EMS dispatch center, the number of patients transferred to emergency departments, the number of MICUs dispatched.

The rationale for the selection and definition of criteria is detailed below:

• (1) Number of patients managed: corresponds to the number of calls resulting in a documented medical decision pertaining to a given patient. This is sensitive indicator of a public health crisis. Established medical records are automatically and continuously updated.
• (2) Number of patients transferred to emergency departments: corresponds to the medical decision to refer a patient to a hospital emergency department and includes both transfer with non-emergency transport ambulance and other rescue vehicles. This information is automatically included in the patient’s file when the decision is made.
• (3) Number of MICUs dispatched: the reference indicator for estimating the number of severely ill patients among the medical records created. This number can indicate care delivered in the patient’s home as well as inter-hospital transfers required, for instance, when a hospital has an insufficient number of beds or is lacking in technological resources. This information is automatically included in the patient’s record when the dispatch decision is made.

All of the above criteria were prospectively and automatically compiled. They were recorded by day and by week for the duration of the time period studied.

Analysis and end-points

Each criterion was compared to its reference. In accordance with previously published methods, the references consisted of records of the same criteria over the previous 5 years. The daily mean was then calculated for each criterion. A variation of over 20% persisting for more than 2 days was considered a marker of the event, defining the related alert threshold. We defined a public health crisis as the point at which the number of patients managed by our SAMU EMS crossed its threshold [^12,13].

We studied the way the criterion increased for each indicator. In order to do that, we calculated the Pearson’s correlation coefficient (R²) corresponding to the evolution of the criteria over time after the first day the thresholds were crossed. Correlation was considered very strong when R² was greater than 0.8 and strong when greater than 0.6 [¹⁴].

Our primary study endpoint was to examine the time between the day the public health crisis threshold was crossed and the day the number of MICUs dispatched crossed the threshold. Our secondary study endpoint was to examine the time between the day the public health crisis threshold was crossed and the day the number of MICUs dispatched reached its maximum.

Key dates

For a better understanding of the chronology of the epidemic in the Seine-Saint-Denis Department of the Greater Paris region and in France, key-dates are reported in Table 1.

Table 1: Key dates of the chronology of the epidemic in France

Results

The reference period extended from 1 January 2015 to 31 December 2019. Over the reference period, the SAMU EMS received 3 381 611 emergency calls, and 1 137 856 (34%) patients were managed. The cases included 341 661 (30%) patients transferred to emergency departments; and 78 246 (7%) MICUs dispatched.

The study period extended from 17 February to 28 March 2020. During the period studied, the SAMU EMS received 166 888 emergency calls, and 56 708 (34%) patients were managed. These cases included 9235 (16%) patients transferred to emergency departments, and 1927 (4%) MICUs dispatched.

The daily number of patients managed crossed the threshold established to define a public health crisis on 25 February 2020. The number of daily patients managed increased linearly (R² = 0.96) and peaked at 2394 on 27 March 2020 (Fig. 1a). The peak was reached 31 days after the crisis threshold was crossed.

Fig. 1: (a) Evolution of the number of patients managed: red curve. Blue curve: average over the reference period (5-year mean); blue zone: 20% variation defined as the threshold for public health crisis; R² = 0.95 (linear). (b) Evolution of the number of MICUs dispatched: Blue curve. Purple curve: average over the reference period (5-year mean); pink zone: 20%; R² = 0.77 (exponential). Red flag: date the threshold was crossed (5-year mean +20%). (c) Evolution of the number of patients transferred to emergency departments: green curve. Brown curve: average over the reference period (5-year mean); green zone: 20% variation; R² = 0.90 (exponential). Primary end-point: lapse of time between the day the threshold of patients managed was crossed and the day the number of MICUs dispatched crossed its threshold. Secondary end-point: lapse of time between the day the number of patients managed crossed its threshold and the day the number of MICUs dispatched reached its maximum.

The daily number of patients transferred to emergency departments crossed its related threshold on 17 March 2020. It then increased exponentially (R² = 0.90). The daily number of patients transferred peaked at 454 on 27 March 2020 (Fig. 1c). The peak was reached 10 days after the crisis threshold was crossed.

The daily number of MICUs dispatched crossed its related threshold on 15 March 2020. It then increased exponentially (R² = 0.77). The daily number of MICUs dispatched peaked at 88 on 26 March 2020 (Fig. 1b). The peak was reached 11 days after the crisis threshold was crossed.

The study’s primary endpoint, the lapse of time between the day the threshold of patients managed, that is, the public health crisis threshold was crossed, and the day the number of MICUs dispatched crossed the threshold was 19 days (Fig. 1). The secondary endpoint, the lapse of time between the day the health crisis threshold was crossed and the day the number of MICUs dispatched reached its maximum was 30 days (Fig. 1).

Discussion

The COVID-19 epidemic reached our department in three consecutive waves which overwhelmed the health care system. All indicators reported here, the number of patients managed, the number of patients transferred to emergency departments, and the number of MICUs dispatched were, at the peak, increased by 396, 210, and 220%, respectively. The number of calls received and the number of patients managed crossed their crisis thresholds 19 days before the number of patients transferred to the hospital (by MICU or not) crossed their respective thresholds representing a 20% increase compared to the previous 5-year mean. The peak of patients transferred to the hospital (by MICU or not) was crossed 10 days later. Hospital admissions and intensive care admissions reached their peaks nationally on March 26 and 27, respectively (Table 1). There was a lapse of time of 31 days between the point at which the public health crisis threshold was crossed and the day the threshold for hospital overcrowding was crossed. In other words, there was a 1-month delay between the moment the health care system was first solicited in the context of an epidemic and the hospitalization of patients with severe forms of the disease. Health care systems must take advantage of this delay to prepare for the third wave, that of patients in critical condition. The identification of this delay may be particularly relevant for countries which, given the trajectory of the pandemic, will likely soon be confronted by the COVID-19 wave [^15,16].

In the current pandemic, the first wave was prompted by French public health officials’ announcement flights from Italy, which borders France (Lombardy, February 23) should be considered equal to those from Wuhan in terms of coronavirus infection risk (Table 1). This date marked the end of a school vacation period, during which many French families vacationed in Italy, and a massive return to school (Table 1). At this point, calls to the Emergency Medical System were essentially for information, with few symptomatic patients. This rise in calls marked the stages (toward March 3, then March 15) that correspond to our restricted capacity to answer the increasing number of calls (Fig. 1a). Each time our answering capacities increased, so did the rise in the number of calls. The second phase, with symptomatic patients requiring hospital transport arrived 3 weeks later. During this 3-week delay, the pre-hospital system became overwhelmed, adding to the already overloaded hospital system. One week later, overloading in ICUs coincided with the threshold crossing for emergency transfers. This increase (results are not presented) impacted MICU at-home patient care as well as inter-hospital transfers. Notably, the delayed overload of transfers to emergency departments and ICUs was not accompanied by a reduction in dispatch center overloading, prohibiting the transfer of personnel from one structure to another. Identifying the first signs of strain on a health care system by a surge in phone calls is of utmost importance. This alert preceded the influx of critical patients in hospitals by almost one month. Health care systems must take advantage of this delay to prepare for the arrival of critical patients. This wave of COVID-19 was prompted by the geographic proximity of the epidemic, as announced by the first cases in the region, the country, or even in a neighboring country. This supposes that crisis thresholds were pre-established, which has been the case in our department since the 2003 heat wave [¹³]. In our experience, when the crisis threshold is crossed, for instance in cases of seasonal influenza, it is surpassed by 70% and for a duration of 3 weeks. A system overload such as the current one has never been observed. A total number of 2700 patients were managed in ICUs in the Seine-Saint-Denis Department of the Greater Paris region. The theoretical capacity is 1200 (Table 1). Specific efforts have been made to increase hospital capacity, including ICU facilities.

Limitations

The principal limitation of this study is the absence of definitive confirmation of COVID-19 infection in our patients, particularly in those who had been transported to the hospital or received medical care by MICU prior to hospital arrival. Nevertheless, in the context of this global pandemic, there is little doubt as to the diagnosis of COVID-19. Another possible limitation is that our results may be underestimated, as they are also self-limiting. Indeed, a call can only be accounted for if it was answered. It is clear that our ability to answer all calls was sometimes limited due to lack of personnel, requiring time to adapt our capacity to the situation. The same is applicable to patient transfers to emergency departments and MICU transfers whose numbers had to be continually increased. Identifying the chronology of events will allow us to adapt our capacity to the situation. A final limitation is the remaining question of whether or not our results can be extrapolated to all Greater Paris, and to other regions and countries.

Conclusion

The COVID-19 epidemic disrupted our region’s health system. Chronological analysis of the beginnings of the outbreak reveal successive phases that we must take advantage of to anticipate the difficulties to come. The anxiety of the general population precedes by approximately 1 month the massive arrival of critical patients. This time frame is the cornerstone of an organized response and can be useful for countries which will soon be affected by the pandemic.

Acknowledgements

Conflicts of interest

FL: Astra-Zeneca, Bayer, BMS, Boehringer-Ingelheim, Medtronic, Merck-Serono, Mundipharma, Novartis, Serb, Teleflex, The Medicine Company. For the remaining authors, there are no conflicts of interest.