Principles of Disease and Epidemiology

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Principles of Disease and Epidemiology

• Ch 14

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Diseases and US

• Pathogen a disease causing microbial growth or
  toxin.
• Disease an abnormality in which the body or part
  is not properly adjusted. The body part is
  overcome by the microbe
• Change in the state of health
• Infection is the invasion and growth of a
  pathogen in the body

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More words

• Host Is an organism that shelters and supports
  the growth of pathogens.
• Pathology scientific study of disease
• Etiology cause of a disease
• Pathogenesis development of disease
• Is this a type of symbiosis?

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Normal Microbiota

• In some cases it is normal for microbes to be
  growing.

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• Most mammals germ free in utero, are colonized
  after birth.
• Microbes that establish permanent colonies inside
  or on outside of the body without causing disease
  are called normal microbiota.
• Transient microbiota are microbes that are stable
  for a time then disappear.

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Symbiosis

• With normal microbiota, usually both species
  benefit from this arrangement.
• Normal microbiota can prevent infections, may
  make necessary vitamins in return for nutrients
  form the host. (is called..
• Opportunistic microbes may cause disease under
  certain instances.
• Probiotics are live microbes applied to or
  ingested into the body, intended to exert a
  beneficial effect.

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Normal Microbiota on the Human Body
Table 14.1
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Skin

• Propionibacterium acnes
• Staphylococcus epidermidis
• Staphylococcus aureus
• Candida spp

• Most microbes are transient on skin.
• Why?

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Eyes

• Basically the same as that found on the skin.
• Eyes have lysozyme, few nutrients, washing by
  tears.

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Nose and throat

• S. aureus
• S. epidermides
• Streptoccoccus pneumoniae
• Haemophilus
• Neisseria

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Mouth

• Streptoccoccus
• Lactobacillus
• Actinomyces
• Bacteroides
• Fusobacterium
• Treponema
• Cornebacterium
• Candida
• Over 200 species

• Idea environment
• Is a diverse environment.
• How do we know what lives in the mouth?

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Large intestine

• Bacteroides
• Fusobacterium
• Lactobacillus
• Enterococcus
• Escherichia
• Enterobacter
• Proteus
• Klebsiella
• Shigella
• Candida

• Is essentially a chemostat
• Has a large resident microbiota

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Urogenital system

• Staphylococcus epidermidis
• Enterococcus
• Lactobacillus
• Pseudomonas
• Klebsiella
• Proteius
• In urethra

• Lactobacilli
• Streptococcus
• Staphylococcus
• Bacteroides
• Clostridium
• Candida albicans
• Trichomonas vaginalis
• in vagina is acidic

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Kochs postulates

• Same pathogen must be present in every case of
  the disease
• Pathogen must be isolated in pure culture
• Pathogen isolated from pure culture must cause
  the same disease in a healthy, susceptible
  laboratory animal.
• Pathogen must be isolated from this animal

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Exceptions to Kochs postulates

• Are modified to establish etiologies of diseases
  caused by viruses and fastidious bacteria, which
  cannot be grown on defined media.
• Some diseases are caused by a variety of
  microbes.
• Some diseases such as S. pyogenes can cause
  several different diseases.

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• Some diseases can only occur in one organism so
  we cannot run the full Kochs postulates.
• Why?

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Disease classification and codification

• Vocab
• Measurements
• Recognition and patterns

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• Symptoms- change in body function
• Diagnosis- identification
• Sign- a measurable change
• Syndrome- a specific group of symptoms or signs
  that always accompanies a specific disease.
• Communicable diseases- transmitted directly or
  indirectly from one host to another.

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• Contagious disease- is easily spread from one
  person to another
• No communicable diseases- are caused by microbes
  that normally grow outside the body and are not
  transmitted from one host to another
• Clostridium tetani

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Where, how bad and how much. Words to describe ID

• Incidence- number of people contracting the
  disease
• Prevalence- number of cases at a particular time
• Frequency- is in terms of sporadic, endemic,
  epidemic and pandemic
• Acute, chronic, subacute and latent
• Herd immunity- is the presence of immunity in
  most of the population

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• Local infection- affects a small area of the body
• Systemic infection- spread throughout the body
• Bacteremia- bacteria in the blood
• Septicemia- bacteria multiply in blood
• Secondary infections- occur after a host is
  weakened from a primary infection
• Subclinical- cannot be measured

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Severity or Duration of a Disease

• Acute disease Symptoms develop rapidly
• Chronic disease Disease develops slowly
• Subacute disease Symptoms between acute and
  chronic
• Latent disease Disease with a period of no
  symptoms when the patient is inactive

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Recognition and patterns of disease

• Predisposing factors make the body more
  susceptible to disease they include
• Gender
• Climate
• Age
• Fatigue
• Nutrition
• Lifestyle
• Drug treatments

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What happens when a disease does occur?

• Incubation period- is the time between the
  initial infection and the first appearance of
  signs and symptoms
• Prodromal- period is the first mild signs and
  symptoms
• Illness- is when the disease is at its height
• Decline- signs and symptoms decline
• Convalescence- time until the body returns to
  predisease state

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The Stages of a Disease
Figure 14.5
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Spreading of Infection

• Reservoir of infection provides pathogen with
  conditions for survival
• Human carriers, asymptomatic or latent
• Animal- zoonoses various routes
• Nonliving Reservoirs water, fertilizer ect

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Transmission of Disease

• Contact transmission
• Direct person to person transmission
• Indirect contact transmission
• Fomite a nonliving transfer (1 meter, soiled
  goods)
• Droplet transmission over short distances
• Vehicle transmission (water, food, air)
• Vectors (mechanical or biological)

Transmission of Disease
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Transmission of Disease
Figure 14.6a 8
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Portals of entry and Exit

• Pathogens have preferred portals of entry and
  exit.
• Most common portals
• Respiratory tract
• Gastrointestinal tract
• Urogenital tract
• Blood to blood

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Transmission of Disease

• Vehicle Transmission by an inanimate
  reservoir (food, water)
• Vectors Arthropods, especially fleas, ticks,
  and mosquitoes
• Mechanical Arthropod carries pathogen on feet
• Biological Pathogen reproduces in vector

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Nosocomial (Hospital-acquired) infections

• 5-15 get infections while in the hospital.
• Microbes in hospital
• Chain of transmission
• Compromised host
• Is a hospital the best place to be if you are
  sick?

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Nosocomial (Hospital-Acquired) Infections

• Are acquired as a result of a hospital stay
• 5-15 of all hospital patients acquire nosocomial
  infections

Figure 14.7, 9
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Nosocomial Infections
ANIMATION Nosocomial Infections Overview
Table 14.5
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Common Causes of Nosocomial Infections
Percentage of Total Infections Percentage Resistant to Antibiotics
Coagulase-negative staphylococci 25 89
S. aureus 16 80
Enterococcus 10 29
Gram-negative rods 23 5-32
C. difficile 13 None
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MRSA

• USA100 92 of health care strains
• USA300 89 of community-acquired strains

Clinical Focus, p. 422
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Which Procedure Increases the Likelihood of
Infection Most?
ANIMATION Nosocomial Infections Prevention
Clinical Focus, p. 422
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Control of Nosocomial

• Aseptic techniques
• Hand washing (40 compliance)
• Infection control staff

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Emerging Infectious diseases

• Ones that are new or changing
• Global warming
• Global transportation
• Antibiotics
• Breakdown in social order
• Governance problems
• Pesticides
• Lack of vaccination
• Lack of reporting

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Epidemiology

• Study of transmission incidence and frequency of
  disease.
• Data are collected and analyzed in descriptive
  epidemiology
• Analytical epidemiology- infected comp to
  uninfected
• Controlled experiments
• Case reporting
• CDC reporting

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• CDC (Centers for Disease Control and Prevention)
  main source of epidemiologic info in US
• Publishes Morbidity and Mortality Weekly Report,
  reports incidence and deaths.

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Centers for Disease Control and Prevention (CDC)

• Collects and analyzes epidemiological information
  in the U.S.
• Publishes Morbidity and Mortality Weekly Report
  (MMWR) www.cdc.gov
• Morbidity incidence of a specific notifiable
  disease
• Mortality deaths from notifiable diseases
• Morbidity rate number of people affected/total
  population in a given time period
• Mortality rate - number of deaths from a
  disease/total population in a given time

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Epidemiology

• The study of where and when diseases occur

Figure 14.11
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New fields of Biological study

• Biological crimes? ASM paper

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Nosocomial outbreak (page 445)

• 7 year period 361 patients developed bacteremia
• Burkholderia cepacia identified (same strain)
• Infection within 36hr of IV
• Disappears hrs after IV removed
• Cleaning insertion site
• Iodine is negative

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Continued

• Not found in povidone-iodine
• In alcohol
• Alcohol purchase as 90 and diluted in pharmacy.
• Used the same 100l container
• Used the same tap water
• Tap water contaminated

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• How do you prevent this from happening?