Series: Mass Gatherings and Infectious Disease

As mentioned last week on The Disease Daily, HealthMap has created a special map to track any infectious disease outbreaks that occur during Hajj. The map was created because a mass gathering, such as Hajj, often strains the local health infrastructure, interfering with its ability to detect and respond to public health threats. In the first piece of this month’s series, we will examine what a mass gathering is, what makes it special, some examples of mass gatherings and actions taken to prevent outbreaks during mass gatherings.

According to the World Health Organization (WHO), a mass gathering, in the context of public health, is “any occasion, either organized or spontaneous, that attracts sufficient number of people to strain the planning and response resources of the community, city or nation hosting the event”. Mass gatherings can be recurrent events that happen in the same place every year (such as Hajj), or recurrent events that happen in different places every year (such as the Olympics or the World Cup), or spontaneous one-time only events (such as a protest). 

Clearly, a lot of advanced planning and organization happens prior to the occurrence of these (expected) events. Some of it is fairly predictable and understood: basic necessities such as water and food and bathroom facilities will be needed. A conference space may be requested. Hotels will need to block off rooms. Tickets will need to be sold and collected. Some of the planning, however, is less familiar to the general public and that is the public health planning.

Mass gatherings demand an enormous amount of preparation by and cooperation between public health officials, politicians, media outlets, laboratory scientists, emergency medical doctors, etc. Prior to a planned mass gathering, public health officials need to take several steps to protect the health of all the attendees and local citizens. One of the first steps is performing a risk assessment. This requires examining the incidence (a measure of disease frequency measuring the number of new cases in a specified population over a specified period of time) and the prevalence (the total number of case in a given population) of all locally endemic diseases. Researchers will need to know what amount of the local population is vulnerable to common infectious diseases. So there might be a study or evaluation of vaccination rates. Public health officials will want to know what infectious diseases are “in season” during the time of the event. Also important is cultural knowledge of those participating in the event. What are greetings like? Do people shake hands or touch cheeks? Are drinks and foods shared? These cultural behaviors and norms impact the spread of infectious agents. What is the duration of the event? And finally, what is the capacity of the host health infrastructure? 

The above questions are used to assess how serious the risk of an infectious disease outbreak is during a given event. But there are several other components to preparing for a mass gathering. What about surveillance for infectious disease during the event? And what about the response, should an outbreak occur? Host countries will need the capacity to store mass amounts of vaccines, to distribute these vaccines and to isolate or quarantine those who have been infected.

Clearly, hosting a mass gathering is no easy task. Saudi Arabia’s Ministry of Health has been preparing all year for the Hajj. As part of that preparation, the Saudi Ministry of Health submitted a report to the WHO weekly epidemiological record indicating what vaccinations visitors are required to have prior to travel (yellow fever – if traveling from a country at risk of yellow fever, meningoccal meningitis, and poliomyelitis – if traveling from a polio-endemic country) and some recommended health measures (receiving a seasonal flu vaccine, carrying out health education programs in country).

Despite all the advanced planning and preparatory action, outbreaks can still occur.  During the 2010 Winter Olympics in Vancouver, there was an outbreak of measles. In prior years, British Columbia experienced around four cases of measles a year. Nine days after the Olympic closing ceremony, an outbreak of measles began that would end with a total of 85 cases.

How can outbreaks occur in spite of all the preparation for a mass gathering? At mass gatherings with international attendees, there are myriad cultures, practices, languages and health behaviors present in the same limited space. Attendees likely share food services and accommodations. Different countries have varying vaccination policies and endemic diseases. Cultural and linguistic differences may make communication of health concerns challenging.

To learn more about mass gatherings and to hear from some experts in the field, check back next week.

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