The dos and donts of outbreak management (Proceedings)

Disease epidemics can progress slowly, affecting only a few animals, or they can progress very rapidly affecting many animals in a wide geographic region, as was seen in the equine herpesvirus-1 (EHV-1) outbreak in 2011 in the western U.S. and Canada.  As the first line of defense, veterinary practitioners must be prepared to recognize epidemics of disease and have a plan in place to logically and systematically collect data and effectively manage the outbreak. 

There are five basic components of managing and investigating an outbreak:  define the problem, treat those affected, prevent disease transmission, determine a cause, and try to prevent its reoccurrence [1]. The first step in defining the problem is to determine if in fact there is an epidemic of disease, i.e. an outbreak.  By definition, an epidemic occurs when the proportion of those at risk of developing disease is greater than what is expected normally.  An owner may call for veterinary assistance, once an epidemic has already been identified, to determine its source.  As the investigator, the tentative diagnoses should be confirmed and a case definition must be developed.  A case definition is crucial to any investigation, allowing for a more focused effort and the collection of appropriate data.  The case definition must include those animals with the primary disease being investigated, but exclude all other healthy animals as well as those affected by other conditions.  In defining a case and investigating an outbreak, consider the 5 W's:  who, what, where, when and why.  By collecting this data the investigator can not only determine the scope of the problem, but can begin to describe the temporal and spatial pattern of disease.  During the investigation, it is prudent to calculate an attack rate, comparing it to the attack rate in a similar population, to determine if an outbreak is actually occurring. Once all data is collected and collated, the investigator can begin to analyze the data simply by looking at attack rates between exposed and non-exposed animals, hopefully identifying the likely source of the outbreak.  A final written report of the investigation findings should be provided, including measures to prevent a future occurrence.

Managing a disease outbreak can be a very strenuous, stressful experience.  It is important for practitioners to be prepared should they be called upon to assist with such an event.  Treatment of affected animals should be initiated as soon as possible, symptomatically until a working diagnosis can be established.  Generic control measures should be put in place, such as movement restriction and personal protective equipment, in an effort at containment.  Practitioners should have a biosecurity toolkit containing personal protective equipment in their practice vehicle for an emergent situation.  It is imperative to break the cycle of transmission.  Keep in mind that infectious disease transmission can occur via multiple avenues including direct contact, indirect contact, and vectors.  An effort should be made to identify the agent, allowing for agent specific treatment and control measures to be implemented.  Communication is an important component of outbreak management, not only to the client but to veterinary authorities if warranted.

As the first line of defense, practitioners must be prepared for the event of an outbreak, developing his/her infection control toolbox prior to calling it into use.  Have a plan in place to systematically compile background information (the 5 W's) and determine if an epidemic is actually occurring.  Take care of not only individual patients, but also of the population (movement control, contact control, hygiene).  Seek expert advice from colleagues and veterinary authorities, and provide excellent communication throughout the duration of the outbreak.

References

Kane, A.J. and Morley, P.S. (1999) How to investigate a disease outbreak. In: Annual Convention of the American Association of Equine Practitioners. pp 137-141.