Does this mean public health had not improved between the great plague and 1900?

There wasn't a lot of improvement until the 19th century when the public health act was bought in and it wasn't until 1867 that the germ theory was discovered by Louis Pasteur. John Snow did a lot of work into the causes of cholera although he never properly found out because it was prior to the germ theory although he did manage to highlight the condition of the poor.