Why did the French call the spread of the Hellfighters band’s music “ragtimitis”?

The term "ragtimitis" was used to describe the infectious popularity and widespread appeal of the music performed by the Harlem Hellfighters regimental band throughout France during World War I.1

Led by the influential bandleader James Reese Europe, the band captivated French audiences with their expressive colors and syncopated rhythms, which were rooted in ragtime and helped introduce jazz to the region. The band's fame became so significant that their regimental commander, William Hayward, leveraged their popularity in his appeals to American leadership to secure combat assignments for the unit, arguing that their cultural impact demonstrated the regiment's value and readiness.231