Microbiology, 2021

16 • Review Questions 681
20. What activity did John Snow conduct, other
than mapping, that contemporary
epidemiologists also use when trying to
understand how to control a disease?
Critical Thinking
22. Why might an epidemiological population in a
state not be the same size as the number of
people in a state? Use an example.
23. Many people find that they become ill with a
cold after traveling by airplane. The air
circulation systems of commercial aircraft use
HEPA filters that should remove any infectious
agents that pass through them. What are the
possible reasons for increased incidence of
colds after flights?
21. Differentiate between droplet vehicle
transmission and airborne transmission.
24. An Atlantic crossing by boat from England to
New England took 60–80 days in the 18th
century. In the late 19th century the voyage took
less than a week. How do you think these time
differences for travel might have impacted the
spread of infectious diseases from Europe to the
Americas, or vice versa?