Different pattern of the second outbreak of COVID-19 in Marseille, France

Area of Science:

• Infectious Diseases
• Epidemiology
• Virology

Background:

• The COVID-19 pandemic presented evolving clinical characteristics and patient demographics since its emergence.
• Understanding temporal shifts in disease presentation is crucial for public health preparedness and clinical management.

Purpose of the Study:

• To compare the clinical and demographic characteristics of COVID-19 patients in Marseille, France, during two distinct periods in 2020: March-April and June-August.
• To identify any changes in disease severity and patient outcomes between these timeframes.

Main Methods:

• Retrospective analysis of patient data including demographics, hospitalization rates, intensive care unit (ICU) transfers, and lethality.
• Evaluation of clinical and biological parameters such as fibrinogen, D-dimer levels, and viral load (cycle threshold).

Main Results:

• Patients in June-August were younger (mean 39.2 vs. 45.3 years) and more frequently male (52.9% vs. 45.6%) compared to March-April.
• Hospitalization (10.7% vs. 18.0%), ICU transfer (0.9% vs. 1.8%), and death (0.1% vs. 1.1%) rates were significantly lower in the summer period.
• Lower mean fibrinogen and D-dimer levels were observed in summer patients, alongside a higher viral load (CT ≤16: 5.1% vs. 3.7%).

Conclusions:

• While age and sex distributions showed minor differences, markers of COVID-19 severity were less prevalent in the summer of 2020.
• A substantial decrease in lethality (approximately tenfold) was associated with the milder disease presentation observed in the later period.