Hi Gwen,
Mortality rates increased(in modern times), as the towns and cities began to fill up with the influx of labour from rural communities, due to the industrial revolution.
Cholera and scarlett fever were killers, as clean and healthy living accomodation became in short supply. Then the availability of decent food became a problem for similar reasons, as well as places to cook it.
Living in filth and squaller, due to overcrowding, quite literally became a breading ground for just about everything imaginable.
A common cold could eventually become a killer as it turned to pneumonia, bronchitis etc.
So I don't think there was one big epidemic during this period, just loads of localised ones, due to the conditions.
Recent times, in 1952, there was the London 'smog', which killed around 4000 people in a week, mostly the young and old. The most vunerable.
Steve.