Also from the Smithsonian: There’s an article on diphtheria. There was an outbreak in 1659 in Mass. In 1735 a child in Kingston, NH had it and it spread to the Kittery/ Hampton Falls area and from there further into Maine and south into Mass. The epidemic lasted until 1740. Rowley lost 1/8 of its population and Byfield 1/7. Your social status did not matter.
Don’t forget to check on what epidemics were happening worldwide if you have folks who went missing. Families lost as many as 8 children. Noah Webster, Cotton Mather, Ernest Caulfield, and others wrote about this sickness. Check the New England Historical Society also.