In early spring 2009, the cdc reported several dozen cases of novel h1n1 influenza ("swine flu") in the united states. by the summer, the number of confirmed cases was reported as over 40,000. the pattern of novel h1n1 cases in the united states represents a(n) disease.

epidemic disease

Explanation:

An epidemic is an infectious and communicable disease that occurs in a community or region and can spread rapidly among people in other regions, leading to an epidemic outbreak. This may be due to a large imbalance (mutation) of the disease-transmitting agent or the emergence of a new (unknown) agent. An example of this can be seen in the question above, where it shows how H1N1 ("swine flu") flu spread rapidly between spring and summer 2009 in the US, presenting a worrying number of infected people.