In case you ever wondered why a large number of your ancestors
disappeared during a certain period in history, this might help.
Epidemics have always had a great influence on people - & thus
influencing as well, the genealogists trying to trace them. Many cases
of people disappearing from records can be traced to their dying during
an epidemic or moving away from the affected area. Some of the major
epidemics in the United States are listed below: 

1657 Boston Measles;
1687 Boston Measles
1690 New York Yellow Fever
1713 Boston Measles
1729 Boston Measles
1732-3 Worldwide Influenza
1738 SC Smallpox
1739-40 Boston Measles
1747 CT,NY,PA,SC Measles
1759 N. Amer [areas inhabited by white people] Measles
1761 North America & West Indies Influenza
1772 North America Measles
1775 N. Amer [especially hard in NE] epidemic Unknown
1775-6 Worldwide [one of the worst epidemics] Influenza
1783 Dover, DE ["extremely fatal"]
Bilious Disorder
1788 Philadelphia & New York Measles
1793 Vermont [a "putrid" fever] & Influenza
1793 VA [killed 500 in 5 counties in 4 weeks] Influenza
1793 Philadelphia [one of the worst epidemics] Yellow Fever
1793 Harrisburg, PA [many unexplained deaths] Unknown
1793 Middletown, PA [many mysterious deaths] Unknown
1794 Philadelphia, PA Yellow Fever
1796-7 Philadelphia, PA Yellow Fever
1798 Philadelphia, PA [one of the worst] Yellow Fever
1803 New York Yellow Fever
1820-3 Nationwide [starts Schuylkill River & spreads] "Fever" 1831-2
Nationwide [brought by English emigrants] Asiatic Cholera 1832 NY
City & other major cities Cholera 1837 Philadelphia Typhus
1841 Nationwide [especially severe in the south] Yellow Fever
1847 New Orleans Yellow Fever
1847-8 Worldwide Influenza
1848-9 North America Cholera
1850 Nationwide Yellow Fever
1850-1 North America Influenza
1852 Nationwide [New Orleans-8,000 die in summer] Yellow Fever
1855 Nationwide [many parts] Yellow Fever
1857-9 Worldwide [one of the greated epidemics] Influenza
1860-1 PA Smallpox
1865-73 Philadelphia, NY, Boston, New Orleans} {Smallpox Baltimore,
Memphis, Washington DC} {Cholera [A series of recurring epidemics of:}
{Typhus {Typhoid
{Scarlet Fever {Yellow Fever
1873-5 North America & Europe Influenza 1878 New Orleans [last great
epidemic] Yellow Fever 1885 Plymouth, PA Typhoid
1886 Jacksonville, FL Yellow Fever
1918 (high point year) Influenza Worldwide more people were
hospitalized in WWI from this epidemic than wounds US Army training
camps became death camps, with 80% death rate in some camps Finally,
these specific instances of cholera were mentioned: 1833 Columbus,
OH
1834 New York City
1849 New York
1851 Coles Co., IL, The Great Plains, & Missouri.