Columbia subject headings:
Epidemics--Puerto Rico--History--20th century.
Influenza Epidemic, 1918-1919--Puerto Rico--History.
Influenza--Puerto Rico--History--20th century.
Harvard subject headings:
Influenza Epidemic, 1918-1919--Puerto Rico.
Princeton subject headings:
Epidemics--Puerto Rico--History--20th century.
Influenza Epidemic, 1918-1919--Puerto Rico--History.
Influenza--Puerto Rico--History--20th century.