Download Ch 14 Principles of Disease and Epidemiology

Principles of Disease and
Epidemiology
Ch 14
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
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?
Normal Microbiota
• In some cases it is normal for microbes to
be growing.
• 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.
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.
Normal Microbiota on the Human
Body
Table 14.1
Skin
• Propionibacterium
acnes
• Staphylococcus
epidermidis
• Staphylococcus
aureus
• Candida spp
• Most microbes are
transient on skin.
• Why?
Eyes
• Basically the same as that found on the
skin.
• Eyes have lysozyme, few nutrients,
washing by tears.
Nose and throat
• S. aureus
• S. epidermides
• Streptoccoccus
pneumoniae
• Haemophilus
• Neisseria
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?
Large intestine
•
•
•
•
•
•
•
•
•
•
Bacteroides
Fusobacterium
Lactobacillus
Enterococcus
Escherichia
Enterobacter
Proteus
Klebsiella
Shigella
Candida
• Is essentially a
chemostat
• Has a large
resident microbiota
Urogenital system
• Staphylococcus
epidermidis
• Enterococcus
• Lactobacillus
• Pseudomonas
• Klebsiella
• Proteius
• In urethra
•
•
•
•
•
•
•
Lactobacilli
Streptococcus
Staphylococcus
Bacteroides
Clostridium
Candida albicans
Trichomonas
vaginalis
• in vagina is acidic
Koch’s 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
Exceptions to Koch’s 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.
• Some diseases can only occur in one
organism so we cannot run the full Koch’s
postulates.
• Why?
Disease classification and
codification
• Vocab
• Measurements
• Recognition and patterns
•
•
•
•
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.
• 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
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
• 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
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
Recognition and patterns of
disease
• Predisposing factors make the body more
susceptible to disease they include
– Gender
– Climate
– Age
– Fatigue
– Nutrition
– Lifestyle
– Drug treatments
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
The Stages of a Disease
Figure 14.5
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
Transmission of Disease
• Contact transmission
– Direct person to person transmission
• Indirect contact transmission
of Disease
– Fomite aTransmission
nonliving transfer
(1 meter, soiled
goods)
• Droplet transmission over short distances
• Vehicle transmission (water, food, air)
• Vectors (mechanical or biological)
Transmission of Disease
Figure 14.6a & 8
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
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
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?
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
Nosocomial Infections
ANIMATION Nosocomial Infections: Overview
Table 14.5
Common Causes of Nosocomial
Infections
Coagulasenegative
staphylococci
S. aureus
Enterococcus
Gram-negative
rods
C. difficile
Percentage of
Total
Infections
25%
Percentage
Resistant to
Antibiotics
89%
16%
10%
23%
80%
29%
5-32%
13%
None
MRSA
• USA100: 92% of health care strains
• USA300: 89% of community-acquired strains
Clinical Focus, p. 422
Which Procedure Increases the
Likelihood of Infection Most?
ANIMATION Nosocomial Infections: Prevention
Clinical Focus, p. 422
Control of Nosocomial
• Aseptic techniques
– Hand washing (40% compliance)
• Infection control staff
Emerging Infectious diseases
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Ones that are new or changing
Global warming
Global transportation
Antibiotics
Breakdown in social order
Governance problems
Pesticides
Lack of vaccination
Lack of reporting
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
• CDC (Centers for Disease Control and
Prevention) main source of epidemiologic
info in US
• Publishes Morbidity and Mortality Weekly
Report, reports incidence and deaths.
•
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
Epidemiology
• The study of
where and when
diseases occur
Figure 14.11
New fields of Biological study
• Biological crimes? ASM paper
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
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
• How do you prevent this from happening?