Page 896 - Clinical Small Animal Internal Medicine

834 Section 9 Infectious Disease

larva as Cochliomyia hominivorax, the New World the area. Published prevalence studies from the literature
VetBooks.ir screwworm, which had been successfully eradicated may provide insight into endemic disease levels in spe-
cific geographic areas or populations. If endemic disease
from the US in the 1960s.
Disease monitoring and surveillance activities can be
formal or informal and help to identify increases in inci- levels are unavailable, levels could be estimated by
extracting diagnosis information from electronic medi-
dence of specific diseases or disease syndromes. Taking cal records in previous years.
the time to formalize a hunch, collect and analyze data,
and report findings to veterinary or public health Step 2: Establish a Case Definition
officials may be the key to early identification of disease
outbreaks within a practice population. Commonly seen diseases with available accurate diag-
nostic tests allow for easy establishment of a working
case definition. For example, outbreaks of canine parvo-
Outbreak Investigations virus are not uncommon and are reliably diagnosed by a
combination of clinical signs and diagnostic test results.
Outbreak investigations are parallel to a diagnostic work‐ The disease under investigation may only present as a
up of an individual patient. A series of steps, performed in collection of clinical signs rather than through isolation
a specific order, provide information which helps describe and identification of a specific pathogen. In this situation,
and diagnose the problem at hand, plus allows insight the case definition would include significant or unique
into measures to mitigate disease and prevent future clinical signs, signalment information, animal location
spread. Sources will vary slightly on the number of steps (area of residence), and time of onset of disease.
involved in an outbreak investigation but this chapter will Additional data from animals who meet the case
focus on a six‐step process for outbreak investigation. definition should be collected to further inform the
The outbreak investigation process mimics the clinical investigation. Data should include pertinent information
investigation process for individual animals with disease: from the patient history, physical exam, and diagnostic
recognize there is a problem, define the problem, gather procedures. Patient outcomes or response to treatments
subjective and objective information to better describe should also be collected and recorded. As the investiga-
the problem, formulate a list of likely differentials, per- tion moves forward, the case definition will be continu-
form diagnostics to rule in or rule out differentials, ally refined in response to new information.
design a treatment plan, and communicate findings with
the client. Goals of an outbreak investigation are to verify Step 3: Descriptive Epidemiology
the pathogen responsible for the disease, identify the
source of disease in the population, determine methods Once the working case definition has been established,
of transmission, and define means to prevent further investigators should review available historical medical
spread and future occurrences. records to identify previous animals meeting the case
definition. This allows for identification of the time point
for the start of the outbreak. Data from previous cases,
Pre‐step (or Step Zero): Establish including species, breed, age, and sex, should be used to
an Investigation Team calculate prevalence of disease in various populations
With outbreaks of food‐borne or infectious disease and further describe the disease epidemiology.
affecting people, a team of physicians and epidemiolo- Generating hypotheses for risk factors for disease will
gists is established prior to beginning an investigation. In depend on this information.
small animal medicine, resources to assist in an investi- Key descriptors for the outbreak investigation include
gation may be available through local departments of temporal and geographic spread of disease. One of the
public health, especially if the outbreak has zoonotic easiest ways to describe these data is through epidemic
potential or may significantly impact the mental well‐ curves (Figure 78.1). Epidemic curves inform hypotheses
being of owners or the community. Assistance may also for disease introduction and transmission, estimate
be available from county or state veterinarians or local incubation periods, recognize possible pathogens, and
colleges of veterinary medicine. identify possible interventions.
Point source epidemic curves are indicative of a com-
mon pathogen exposure in a group of animals in a single
Step 1: Confirm Presence of Disease Outbreak
or relatively brief time point. They are characterized by a
Before moving forward with an investigation, confirma- sharp slope at the beginning of the outbreak and a more
tion of the presence of disease above normal levels gradual slope at the end. For infectious diseases, spread
must occur. Ideally, this would involve comparing current of the disease is limited to a single incubation period and
disease levels with historic endemic levels of disease in further spread into naive populations does not occur.