Appendix A

Glossary

Acute disseminated encephalomyelitis (ADEM): An acute demyelinating disorder of the central nervous system in which focal demyelination is present throughout the brain and spinal cord.1

Afebrile convulsions: A convulsion that occurs in the absence of fever.2

Amyotrophic lateral sclerosis: A fatal degenerative disease involving the corticobulbar, corticospinal, and spinal motor neurons, manifested by progressive weakness and wasting of muscles innervated by the affected neurons; fasciculations and cramps commonly occur.1

Anaphylaxis/anaphylactic shock: An immediate and severe allergic reaction to a substance.3

Arthralgia: Pain in a joint.1

Arthritis: Inflammation of one or more joints, which results in pain, swelling, stiffness, and limited movement.2

Arthropathy: Any disease affecting a joint.1

Asthma: An inflammatory disorder of the airways, which causes attacks of wheezing, shortness of breath, chest tightness, and coughing.2



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Appendix A Glossary Acute disseminated encephalomyelitis (ADEM): An acute demyelinating disorder of the central nervous system in which focal demyelination is pres- ent throughout the brain and spinal cord.1 Afebrile convulsions: A convulsion that occurs in the absence of fever.2 Amyotrophic lateral sclerosis: A fatal degenerative disease involving the corticobulbar, corticospinal, and spinal motor neurons, manifested by pro- gressive weakness and wasting of muscles innervated by the affected neu- rons; fasciculations and cramps commonly occur.1 Anaphylaxis/anaphylactic shock: An immediate and severe allergic reaction to a substance.3 Arthralgia: Pain in a joint.1 Arthritis: Inflammation of one or more joints, which results in pain, swell- ing, stiffness, and limited movement.2 Arthropathy: Any disease affecting a joint.1 Asthma: An inflammatory disorder of the airways, which causes attacks of wheezing, shortness of breath, chest tightness, and coughing.2 635

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636 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY Ataxia: An inability to coordinate muscle activity during voluntary move- ment; most often results from disorders of the cerebellum or the posterior columns of the spinal cord; may involve the limbs, head, or trunk.1 Autism: A developmental disorder that appears in the first 3 years of life, and affects the brain’s normal development of social and communication skills.2 Autoimmune hepatitis: Chronic liver disease of unknown etiology char- acterized by histologic presence of periportal hepatitis with plasma cell infiltration, hypergammaglobulinemia, and presence of autoantibodies in the serum.1 Bell’s palsy: Paresis or paralysis, usually unilateral, of the facial muscles, caused by dysfunction of the seventh cranial nerve; probably due to a viral infection; usually demyelinating in type.1 Bias: Systematic deviation of results or inferences from truth; processes leading to such deviation. An error in the conception and design of a study—or in the collection, analysis, interpretation, reporting, publication, or review of data—leading to results or conclusions that are systematically (as opposed to randomly) different from the truth.4 Brachial neuritis: Inflammation of nerves in the arm causing muscle weak- ness and pain.5 Case-crossover study: The method is akin to a matched case-control study, in which the controls are sampled from the person-time of the case prior to the event. Vaccinations are ascertained in a defined time period immediately prior to the event and in one or several earlier control periods of the same duration. This produces, for each case, a matched set of exposure variables corresponding to the event and control periods, which may be analyzed as in a case-control study.6 Case-control study: The observational epidemiologic study of persons with the disease (or another outcome variable) of interest and a suitable control group of persons without the disease (comparison group, reference group). The potential relationship of a suspected risk factor or an attribute to the disease is examined by comparing the diseased and nondiseased subjects with regard to how frequently the factor or attribute is present (or, if quantitative, the levels of the attribute) in each of the groups (diseased and nondiseased).4

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637 APPENDIX A Case-only study: A method that analyzes data from a case series. It may be seen as an epidemiologic equivalent of the “thought experiment” used by theoretical physicists. It is used in the case-crossover study, in case-specular designs, and in molecular and genetic epidemiology to assess relationships between environmental exposures and genotypes.4 Case report: Detailed description of a few patients or clinical cases (fre- quently, just one sick person) with an unusual disease or complication, uncommon combinations or diseases, or an unusual or misleading semiol- ogy, cause, or outcome.4 Case series: A collection of patients with common characteristics used to describe some clinical, pathophysiological, or operational aspect of a dis- ease, treatment, or diagnostic procedure. Some are similar to the larger case reports and share the virtues of this design.4 Cerebellar ataxia: Loss of muscle coordination caused by disorders of the cerebellum.1 Chronic fatigue syndrome: Syndrome of persistent incapacitating weakness or fatigue, accompanied by nonspecific somatic symptoms, lasting at least 6 months, and not attributable to any known cause.1 Chronic headache: Pain in various parts of the head, not confined to the area of distribution of any nerve.1 Chronic inflammatory disseminated polyneuropathy (CIDP): An uncom- mon, acquired, demyelinating sensorimotor polyneuropathy, clinically characterized by insidious onset, slow evolution (either steady progression or stepwise), and chronic course; symmetric weakness is a predominant symptom, often involving proximal leg muscles, accompanied by paresthe- sias, but not pain; CSF examination shows elevated protein, whereas elec- trodiagnostic studies reveal evidence of a demyelinating process, primarily conduction slowing rather than block; sometimes responds to prednisone.1 Chronic urticaria: A form of urticaria in which the wheals recur frequently, or persist.1 Cohort study: The analytic epidemiologic study in which subsets of a de- fined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the occurrence of a given disease or other outcomes. The main feature of cohort study is observation of large numbers

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638 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY over a long period (commonly years), with comparison of incidence rates in groups that differ in exposure levels. The alternative terms for a cohort study (i.e., follow-up, longitudinal, and prospective study) describe an es- sential feature of the method, which is observation of the population for a sufficient number of person-years to generate reliable incidence or mortal- ity rates in the population subsets. This generally implies study of a large population, study for a prolonger period (years), or both. The denomina- tors used for analysis may be persons or person-time.4 Complex regional pain syndrome (CRPS): A condition of chronic, severe, and often burning pain usually of part or all of one or more extremities that typically occurs following an injury, that is often accompanied by swelling, skin discoloration, allodynia, abnormal sweating, and impaired motor func- tion in the affected area, and that is of unknown pathogenesis.3 Confounding: Loosely, the distortion of a measure of the effect of an expo- sure on an outcome caused by the association of the exposure with other factors that influence the occurrence of the outcome. Confounding occurs when all or part of the apparent association between the exposure and outcome is in fact accounted for by other variables that affect the outcome and are not themselves affected by exposure.4 Convulsion: See Seizure. Crossover experiment: A method of comparing two (or more) treatments or interventions in which subjects, upon completion of one treatment, are switched to the other treatment or intervention. In the case of two treat- ments, A and B, half the patients are randomly allocated to receive these in the order “A first, then B” and half to receive them in the order “B first, then A.” The outcomes cannot be permanent changes (e.g., they can be symptoms, functional capacity).4 Deltoid bursitis (frozen shoulder): A condition in which joint motion be- comes restricted because of inflammatory thickening of the capsule; a com- mon cause of shoulder stiffness.1 Demyelination: Loss of myelin with preservation of the axons or fiber tracts.1 Diphtheria: A specific infectious disease due to the bacterium Corynebac- terium diphtheriae and its highly potent toxin; marked by severe inflam- mation that can form a membranous coating, with formation of a thick fibrinous exudate, of the mucous membrane of the pharynx, the nose, and

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639 APPENDIX A sometimes the tracheobronchial tree; the toxin produces degeneration in peripheral nerves, heart muscle, and other tissues; diphtheria had a high fatality rate, especially in children, but is now rare because of an effective vaccine.1 Disseminated varicella: The spreading of the vesicular rash beyond the dermatome involved in the vaccination.5 Embolism: Obstruction or occlusion of a vessel by an embolus.1 Encephalitis: Irritation and swelling (inflammation) of the brain, most often due to infections.2 Encephalopathy: A general term describing brain dysfunction. Examples include encephalitis, meningitis, seizures, and head trauma.5 Erythema nodosum: A panniculitis marked by the sudden formation of painful nodes on the extensor surfaces of the lower extremities, with le- sions that are self-limiting but tend to recur; associated with arthralgia and fever; may be the result of drug sensitivity or associated with sarcoidosis and various infections.1 Febrile convulsions: A brief seizure, lasting less than 15 minutes, seen in a neurologically normal infant or young child, associated with fever.1 Fibromyaligia: A chronic disorder characterized by widespread pain, ten- derness, and stiffness of muscles and associated connective tissue structures that is typically accompanied by fatigue, headache, and sleep disturbances.3 Guillain-Barré syndrome (GBS): An acute, immune-mediated disorder of peripheral nerves, spinal roots, and cranial nerves, commonly presenting as a rapidly progressive, areflexive, relatively symmetric ascending weakness of the limb, truncal, respiratory, pharyngeal, and facial musculature, with variable sensory and autonomic dysfunction; typically reaches its nadir within 2–3 weeks, followed initially by a plateau period of similar duration, and then subsequently by gradual but complete recovery in most cases.1 Hearing loss: A reduction in the ability to perceive sound; may range from slight inability to complete deafness.1 Hepatitis: Inflammation of the liver, due usually to viral infection but some- times to toxic agents.1

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640 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY Hepatitis A: A viral disease with a short incubation period (usually 15–50 days), caused by hepatitis A virus, a member of the family Picornaviridae, often transmitted by fecal-oral route; may be inapparent, mild, severe, or occasionally fatal and occurs sporadically or in epidemics, commonly in school-age children and young adults; necrosis of periportal liver cells with lymphocytic and plasma cell infiltration is characteristic, and jaundice is a common symptom.1 Hepatitis B: A viral disease with a long incubation period (usually 50–160 days), caused by a hepatitis B virus, a DNA virus and member of the family Hepadnaviridae, usually transmitted by injection of infected blood or blood derivatives or by use of contaminated needles, lancets, or other instruments or by sexual transmission; clinically and pathologically similar to viral hepatitis type A, but there is no cross-protective immunity; HBsAg is found in the serum and the hepatitis delta virus occurs in some patients. May lead to acute or chronic liver disease.1 Herpes zoster: An infection caused by a herpesvirus (varicella zoster virus), characterized by an eruption of groups of vesicles on one side of the body following the course of a nerve due to inflammation of ganglia and dorsal nerve roots resulting from activation of the virus, which in many instances has remained latent for years following a primary chickenpox infection; the condition is self-limited but may be accompanied by or followed by severe postherpetic pain. Also known as the shingles.1 Human papillomavirus (HPV): An icosahedral DNA virus, 55 nm in diam- eter, of the genus Papillomavirus, family Papovaviridae; certain types cause cutaneous and genital warts; other types are associated with severe cervical intraepithelial neoplasia and anogenital and laryngeal carcinomas.1 Hypercoagulable states: C haracterized by abnormally increased coagulation.1 Immune thrombocytopenic purpura (ITP): A systemic illness characterized by extensive ecchymoses and hemorrhages from mucous membranes and very low platelet counts; resulting from platelet destruction by macrophages due to an antiplatelet factor; childhood cases are usually brief and rarely present with intracranial hemorrhages, but adult cases are often recurrent and have a higher incidence of grave bleeding, especially intracranial. Also known as idiopathic thrombocytopenic purpura.1 Infantile spasms: An epileptic disorder characterized by flexion spasms of the neck, trunk, and limbs and psychomotor retardation.7

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641 APPENDIX A Influenza: An acute infectious respiratory disease, caused by Influenza vi- ruses, which are in the family Orthomyxoviridae, in which the inhaled virus attacks the respiratory epithelial cells of those susceptible and produces a catarrhal inflammation; characterized by sudden onset, chills, fever of short duration (3–4 days), severe prostration, headache, muscle aches, and a cough that usually is dry and may be followed by secondary bacterial infections that can last up to 10 days.1 Insulin-dependent diabetes mellitus: Chronic (lifelong) disease that occurs when the pancreas does not produce enough insulin to properly control blood sugar levels, also known as type 1 diabetes.2 Juvenile idiopathic arthritis: Chronic arthritis beginning in childhood, most cases of which are pauciarticular, i.e., affecting few joints.1 Measles: An acute exanthematous disease, caused by measles virus (genus Morbillivirus), a member of the family Paramyxoviridae, and marked by fever and other constitutional disturbances, a catarrhal inflammation of the respiratory mucous membranes, and a generalized dusky red maculopapu- lar eruption; the eruption occurs early on the buccal mucous membrane in the form of Koplik spots, a manifestation useful in early diagnosis; average incubation period is from 10–12 days.1 Measles inclusion body encephalitis: A rare chronic, progressive encephali- tis that affects primarily children and young adults, caused by the measles virus. Death usually occurs within 3 years.1 Meningitis: Inflammation of the membranes of the brain or spinal cord.1 Meningoencephalitis: An inflammation of the brain and its membranes.1 Multiple sclerosis (MS): Common demyelinating disorder of the central ner- vous system, causing patches of sclerosis (plaques) in the brain and spinal cord; occurs primarily in young adults, and has protean clinical manifesta- tions, depending on the location and size of the plaque; typical symptoms include visual loss, diplopia, nystagmus, dysarthria, weakness, paresthesias, bladder abnormalities, and mood alterations; characteristically, the plaques are “separated in time and space” and clinically the symptoms show exac- erbations and remissions.1 Mumps: An acute infectious and contagious disease caused by a mumps vi- rus of the genus Rubulavirus and characterized by fever, inflammation and

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642 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY swelling of the parotid gland, and sometimes of other salivary glands, and occasionally by inflammation of the testis, ovary, pancreas, or meninges.1 Myocardial infarction: Infarction of a segment of heart muscle, usually due to occlusion of a coronary artery.1 Myocarditis: Inflammation of the muscular walls of the heart.1 Myoclonic epilepsy: Epilepsy marked by myoclonic seizures.3 Neisseria meningitides: A bacterial species found in the nasopharynx of humans but not in other animals; the causative agent of meningococcal meningitis and meningicoccemia; virulent organisms are strongly gram neg- ative and occur singly or in pairs; in the latter case the cocci are elongated and are arranged with long axes parallel and facing sides kidney shaped; groups characterized by serologically specific capsular polysaccharides are designated by capital letters.1 Nested case-control study: An important type of case-control study in which cases and controls are drawn from the population in a fully enumer- ated cohort. Typically, some data on some variables are already available about both cases and controls; thus concerns about differential (biased) misclassification of these variables can be reduced (e.g., environmental or nutritional exposures may be analyzed in blood from cases and controls collected and stored years before disease onset). A set of controls is selected from subjects (i.e., noncases) at risk of developing the outcome of interest at the time of occurrence of each case that arises in the cohort.4 Neuritis: Inflammation of a nerve.1 Neuromyelitis optica: A demyelinating disorder consisting of a transverse myelopathy and optic neuritis.1 Neuropathy: A disease involving the cranial nerves or the peripheral or autonomic nervous system.1 Oculorespiratory syndrome: A usually transient syndrome of bilateral red eyes and upper respiratory symptoms, including cough, wheezing, chest discomfort, sore throat, and occasionally facial edema, following influenza vaccination.1 Opsoclonus myoclonus syndrome: A rare neurological disorder character- ized by an unsteady, trembling gait, myoclonus (brief, shock-like muscle

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643 APPENDIX A spasms), and opsoclonus (irregular, rapid eye movements). Other symptoms may include difficulty speaking, poorly articulated speech, or an inability to speak. A decrease in muscle tone, lethargy, irritability, and malaise (a vague feeling of bodily discomfort) may also be present.8 Optic neuritis: Inflammation of the optic nerve.1 Pancreatitis: Inflammation of the pancreas.1 Pertussis: An acute infectious inflammation of the larynx, trachea, and bronchi caused by Bordetella pertussis; characterized by recurrent bouts of spasmodic coughing that continues until the breath is exhausted, then ending in a noisy inspiratory stridor (the “whoop”) caused by laryngeal spasm.1 Pneumonia: Inflammation of the lung parenchyma characterized by consoli- dation of the affected part, the alveolar air spaces being filled with exudate, inflammatory cells, and fibrin.1 Polyarteritis nodosa: Segmental inflammation, with infiltration by eosino- phils, and necrosis of medium-sized or small arteries, more common in males, with varied symptoms related to involvement of arteries in the kid- neys, muscles, gastrointestinal tract, and heart.1 Psoriatic arthritis: The concurrence of psoriasis and polyarthritis, resem- bling rheumatoid arthritis but thought to be a specific disease entity, sero- negative for rheumatoid factor and often involving the digits.1 Randomized controlled trial (RCT): An epidemiologic experiment in which subjects in a population are randomly allocated into groups, usually called study and control groups, to receive or not receive an experimental preven- tive or therapeutic procedure, maneuver, or intervention. The results are as- sessed by rigorous comparison of rates of disease, death, recovery, or other appropriate outcome in the study and control groups. RCTs are generally regarded as the most scientifically rigorous method of hypothesis testing available in epidemiology and medicine. Nonetheless, they may suffer seri- ous lack of generalizability, due, for example, to the nonrepresentativeness of patients who are ethically and practically eligible, chosen, or consent to participate.4 Reactive arthritis: Sterile, usually transient polyarthropathy following vari- ous infectious diseases.1

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644 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY Retrospective study: A research design used to test etiologic hypotheses in which inferences about exposure to the putative causal factor(s) are derived from data relating to characteristics of the persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or other outcome or condition of interest, and their characteristics and past experiences are compared with those of unaffected persons.4 Rheumatoid arthritis: A generalized disease, occurring more often in women, which primarily affects connective tissue; arthritis is the dominant clinical manifestation, involving many joints, especially those of the hands and feet, accompanied by thickening of articular soft tissue, with extension of synovial tissue over articular cartilages, which become eroded; the course is variable but often is chronic and progressive, leading to deformities and disability.1 Rubella: An acute but mild exanthematous disease caused by rubella virus (Rubivirus family Togaviridae), with enlargement of lymph nodes, but usually with little fever or constitutional reaction; a high incidence of birth defects in children results from maternal infection during the first trimester of fetal life (congenital rubella syndrome).1 Seizure: A violent spasm or series of jerkings of the face, trunk, or extremi- ties. Also known as convulsions.1 Self-controlled case-series study: The method, like the case-crossover method, uses cases as their own controls. However, the similarity stops there, as the case-series method derives from cohort rather than case- control logic. In particular, ages at vaccination are regarded as fixed, and the random variable of interest is the age at adverse event, conditionally on its occurrence within a predetermined observation period.6 Serum sickness: An immune complex disease appearing some days (usually 1–2 weeks) after injection of a foreign serum or serum protein, with local and systemic reactions such as urticaria, fever, general lymphadenopathy, edema, arthritis, and occasionally albuminuria or severe nephritis; origi- nally described in patients receiving serotherapy.1 Shingles: See Herpes zoster. Small fiber neuropathy: Neuropathy of small unmyelinated axons.8

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645 APPENDIX A Stroke: Any acute clinical event, related to impairment of cerebral circula- tion, that lasts longer than 24 hours.1 Sudden death: Unexpected death that is instantaneous or occurs within minutes or hours from any cause other than violence.3 Sudden infant death syndrome (SIDS): The sudden death of an apparently healthy infant that remains unexplained after all known possible causes have been ruled out through autopsy, death scene investigation, and review of the medical history.1 Surveillance: Systematic and continuous collection, analysis, and interpreta- tion of data, closely integrated with the timely and coherent dissemination of the results and assessment to those who have the right to know so action can be taken. It is an essential feature of epidemiologic and public health practice. The final phase in the surveillance chain is the application of in- formation to health promotion and to disease prevention and control. A surveillance system includes functional capacity for data collection, analy- sis, and dissemination linked to public health programs.4 Syncope: Loss of consciousness and postural tone caused by diminished cerebral blood flow.1 Systemic lupus erythematosus: An inflammatory connective tissue disease with variable features, frequently including fever, weakness and fatigability, joint pains or arthritis resembling rheumatoid arthritis, diffuse erythema- tous skin lesions on the face, neck, or upper extremities, with liquefaction degeneration of the basal layer and epidermal atrophy, lymphadenopathy, pleurisy or pericarditis, glomerular lesions, anemia, hyperglobulinemia, and a positive LE cell test result, with serum antibodies to nuclear protein and sometimes to double-stranded DNA and other substances.1 Tetanus: A disease marked by painful tonic muscular contractions, caused by the neurotropic toxin (tetanospasmin) of Clostridium tetani acting on the central nervous system.1 Thrombocytopenia: A condition in which an abnormally small number of platelets is present in the circulating blood.1 Thromboembolic events: An occurrence that induces thromboembolism.2 Thromboembolism: Condition in which a blood clot forms in a vein that is deep inside the body; also known as deep venous thrombosis.2

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646 ADVERSE EFFECTS OF VACCINES: EVIDENCE AND CAUSALITY Transverse myelitis: An abrupt onset inflammatory process involving almost the entire thickness of the spinal cord but of limited longitudinal extent, generally one or a few segments; of multiple etiologies, the most common being viral and postviral causes, and multiple sclerosis.1 Urticaria: An eruption of itching wheals, collquially called hives, usually of systemic origin; it may be due to a state of hypersensitivity to foods or drugs, foci of infection, physical agents (heat, cold, light, friction), or psychic stimuli.1 Vaccine Adverse Event Reporting System (VAERS): A database managed by the Centers for Disease Control and Prevention and the Food and Drug Ad- ministration. VAERS provides a mechanism for the collection and analysis of adverse events associated with vaccines currently licensed in the United States. Reports to VAERS can be made by the vaccine manufacturer, recipi- ent, their parent/guardian, or health care provider. For more information on VAERS call (800) 822-7967.5 Vaccine Safety Datalink Project (VSD): To increase knowledge about vac- cine adverse events, the Centers for Disease Control and Prevention has formed partnerships with eight large health management organizations to continually evaluate vaccine safety. The project contains data on more than 6 million people. Medical records are monitored for potential adverse events following immunization. The VSD project allows for planned vaccine safety studies as well as timely investigations of hypothesis.5 Varicella: An acute contagious disease, usually occurring in children, caused by the varicella zoster virus genus, Varicellovirus, a member of the family Herpesviridae, and marked by a sparse eruption of papules, which become vesicles and then pustules, like that of smallpox although less severe and varying in stages, usually with mild constitutional symptoms; incubation period is about 14–17 days.1 Vasculitis: Inflammation of a blood vessel (arteritis, phlebitis) or lymphatic vessel (lymphangitis).1 SOURCES 1This definition was obtained from Stedman’s Medical Dictionary. The citation for the term is Stedman, Thomas Lathrop. 2006. Stedman’s medical dictionary. Philadelphia: Lippincott Williams & Wilkins. © 2006. 2This definition was obtained by searching the term in the A.D.A.M. Medical Encyclopedia, a source used by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) at the National Institutes of Health (NIH). The citation

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647 APPENDIX A for the A.D.A.M. Medical Encyclopedia term is A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M., Inc.; © 2010, and the specific term can be obtained on the following website: http://www.ncbi.nlm.nih.gov/pubmedhealth/s/diseases_and_conditions. 3This definition was obtained by searching the term in the Merriam-Webster Medical Dictionary, a source used by National Institutes of Health’s Medline Plus website, which is produced by the National Library of Medicine. The citation for the Merriam-Webster Medi- cal Dictionary term is Merriam-Webster Medical Dictionary [Internet]. [Springfield (MA)]: Merriam-Webster, Incorporated; © 2003, and the specific term can be obtained on the follow- ing website: http://www.nlm.nih.gov/medlineplus/mplusdictionary.html. 4This definition was obtained from A Dictionary of Epidemiology, fifth edition, a handbook sponsored by the International Epidemiology Association. The citation for the term is: Porta, M. 2008. A Dictionary of Epidemiology, 5th ed. New York, NY: Oxford University Press. © 2008. 5This definition was obtained from the Centers for Disease Control and Prevention as de- fined on the following webpage: http://www.vaccines.gov/more_info/glossary/index.html. 6This definition was obtained from Farrington, C. P. 2004. Control without separate con- trols: Evaluation of vaccine safety using case-only methods. Vaccine 22(15-16):2064-2070. Elsevier Ltd. © 2004. 7This definition was obtained from Aminoff, M. J., and R. B. Daroff. 2003. Encyclopedia of the neurological sciences. 1st ed. 4 vols. Amsterdam: Boston. © 2003. 8This definition was obtained from the National Institute of Neurological Disorders and Stroke (NINDS) by searching the following webpage for the term: http://www.ninds.nih.gov/.

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