Practical Clinical Epidemiology for the Veterinarian

Aurora Villarroel

• Publisher: Wiley-American Ceramic Society
• Year: 2015
• Print ISBN:
  9781118472064
• eBook ISBN:
  9781118472040
• Edition: 1
• Topic: Medicina
• Subtopic: Medicina veterinaria

Practical Clinical Epidemiology for the Veterinarian provides thorough coverage of the fundamentals of epidemiological concepts, situated within the context of daily clinical practice.

• Examines epidemiology from the lens of daily clinical practice to offer a truly practical approach
• Demonstrates the relevance of epidemiology to clinical problems faced in the field using practical examples to clarify the concepts
• Includes clinical cases from all species, with an emphasis on small animal and equine medicine, to demonstrate the concepts
• Uses an easy-to-read approach, with graphs, flowcharts, and tables to promote understanding
• Includes access to a companion website with exercises for study and review

1
Describing health and disease

Disease does not occur at random; if it were we would not have a job! There is a pattern for every disease; we just need to find it.

To find how disease behaves we need to answer the following questions:

• What is the problem?
• Who gets diseased?
• Where is the disease concentrated?
• When does disease occur?

Answering all these questions (the essence of epidemiology is describing disease in populations) should lead us to the answer of the ultimate question we have about a certain disease (why does it happen?) and enable us to prevent it.

Case definition

The best explanation of the true substance of the word “definition” in matters pertinent to epidemiology comes from combining two of the meanings of the “definition”: (i) an exact statement or description of the nature, scope, or meaning of something, and (ii) the degree of distinctness in outline of an object (Oxford Dictionaries online).¹ Therefore, the more carefully we describe things, the more distinctness we achieve. In defining words, it is important to avoid using another word with the same root as the one we are defining. When defining a case, it tends to be more complete and accurate when following the same rule of not using words with the same root.

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Example

When asked to define a diarrheic patient, simply stating it is a dog with diarrhea does not give much distinction to the case. However, if we define a diarrheic patient as a dog with feces that are not well-formed and cannot be picked up without leaving a mark on the ground gives a clear-cut characteristic that allows anyone to categorize a patient as having diarrhea or not.

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What is the problem?

Before we start looking into who is diseased or where it is, we need to define what we are going to consider a diseased individual looks like; in other words, we need a case definition. This seems silly at first, but it is the most important step in any study or investigation and is not so clear-cut if you look deeper.

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Example

Let us suppose we want to investigate if there is a problem of parvovirus in a kennel. How would you define a case of parvovirus? Most people would say a puppy with diarrhea. The problems with this simple definition of a case of parvovirus are as follows:

• There are other causes of diarrhea in puppies, so you may be overestimating how much parvovirus infection there truly is.
• Parvovirus may have asymptomatic infections, so you may be underestimating infection.
• Parvovirus can have other clinical signs without diarrhea, such as lethargy, anorexia, fever, vomiting, and severe weight loss, so you may be underestimating infection by looking only at puppies with diarrhea.
• How old can a dog be while still being considered a puppy? In other words, what is the “case definition” of a puppy?

To get the best estimate of truly infected dogs in a population, we would have to better define a case of parvovirus infection. An example could be “dogs less than 9 months old with a positive fecal ELISA test for parvovirus.” This definition would minimize the number of dogs with diarrhea due to other causes (because they have to have a positive ELISA test), and it would also minimize the number of dogs excluded because they did not have diarrhea.

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The importance of case definition becomes paramount when comparing research studies about a certain disease. If two studies do not have the same case definition, the results of both studies cannot be compared directly.

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Example

A study on hip dysplasia in dogs (Paster et al. 2005) showed that inclusion of the caudal curvilinear osteophyte in the definition of canine hip dysplasia significantly altered the diagnosis of a large proportion of dogs, usually toward a higher s...

Table of contents

• Cover
• Title page
• Table of Contents
• Preface
• Acknowledgments
• About the companion website
• 1 Describing health and disease
• 2 Basic epidemiology concepts
• 3 Evidence-based medicine for the veterinarian
• 4 Study designs
• 5 Causation versus association
• 6 Diagnostic tests
• 7 Outbreak investigations
• Glossary
• Formulas
• Final word
• References
• Index
• End User License Agreement