Mass gatherings can facilitate infectious disease transmission

May 22, 2019

Photo Credit: Mauricio Ayovi

Mass gatherings have long been known to increase risks of infectious disease outbreaks. Music festivals, sporting events, religious pilgrimages, and other assemblies of significant numbers of people create conditions that strain local infrastructure, increase contact rates, overextend sanitation infrastructure, and thereby facilitate the spread of pathogens. At the same time, variations in rainfall, temperature and other climatic factors in these settings can further affect the transmission of diarrheal diseases.

In a new study published in the American Journal of Epidemiology, a team of interdisciplinary researchers found that even modestly sized community gatherings were associated with increased transmission of diarrheal diseases—a major global killer—in a study region in Esmeraldas, Ecuador.

“While most of our understanding of the role of social gatherings in infectious disease spread comes from events of thousands or millions, our work shows that cultural, religious or social gatherings of just hundreds or dozens of people can be accompanied by a significant increase in endemic diarrheal diseases,” says Philip Collender, an environmental health scientist at the School of Public Health who led the study.

Using a set of statistical time-series models incorporating environmental, ethnographic, and health data, the researchers found that mass gatherings were associated with an average 21 percent increase in disease incidence in host villages two weeks after a rainfall event. The excess risk jumped to 51 percent when gatherings included substantial inbound travel.

“Our results imply that not every gathering contributes equally to disease risk,” says Collender. “We see evidence that the events associated with the highest risk are those involving the most crowding, which is consistent with our understanding of the mechanisms that contribute to disease transmission during gatherings.”

Diarrheal diseases lead to about 2 million deaths each year, mostly among children. In communities that have limited access to sanitation and safe water, an influx of visitors can easily double the local population, overwhelming protective infrastructure and facilitating the spread of pathogens that lead to these diseases.

Preventing these outbreaks is a high priority for improving global public health. “Philip’s research shows that certain social and cultural events are predictable foci of endemic disease transmission,” says Justin Remais, head of Environmental Health Sciences at the School of Public Health and principle investigator of the study. “By anticipating risks associated with these gatherings, and collaborating with the local organizations that plan and organize them, we have an opportunity to prevent disease transmission through efforts to improve water, sanitation, and hygiene resources during and after the event.”

The research is applicable to a range of environmental risks that are exacerbated by gaps in the resources necessary to prevent disease. “This study shows that disease transmission is a balance between increased risk factors and the resources available to provide facilities for sanitation, safe food preparation, and safe water,” says Tom Torgersen, a program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “This knowledge is applicable to many other diseases.”

The research team also included scientists from the University of Michigan, Emory University, Trinity College, and Universidad San Francisco de Quito in Ecuador. The study was supported by grants from the National Institute of Allergy and Infectious Diseases, the National Science Foundation, and the National Institute of Health’s Fogarty International Center.

By Austin Price