After the H1N1 influenza was first identified in 2009, numerous strategies were employed in an unsuccessful attempt to contain the disease’s spread. While the outbreak was less severe than feared, it eventually infected one out of six Americans and led to thousands of deaths, according to the Centers for Disease Control and Prevention. While the virus was extensively mapped as it spread around the globe, there was less study on its propagation within small or contained communities.

A 2011 study in the Journal of Virology by researchers at Pennsylvania State University, “Extensive Geographical Mixing of 2009 Human H1N1 Influenza A Virus in a Single University Community,” observed the spread of H1N1 virus within the student body of the University of California, San Diego (UCSD), between October and November 2009.

The study’s findings include:

• Between 24 and 33 separate introductions of different strains of the H1N1 virus were made within the student body in just one month.
• Within the UCSD community, there were seven clusters of affected students. Three comprised only two separate H1N1 sequences, two others contained three sequences, one cluster comprised four sequences, and the seventh had no less than 14 distinct sequences of the virus.
• There was limited geographical clustering of infections. In some cases, students living in the same dormitory who became ill on the same day were found to have been infected with separate strains of H1N1.
• Overall, there was no evidence for a single-point source outbreak, in which one H1n1 virus entered the UCSD community and diffused through the interconnected population.

The study indicates a high level of variety within the H1N1 virus, the authors state. The implications are “likely to impede community-based methods for [virus] control, including class cancellations, quarantine, and chemoprophylaxis.”

Tags: California