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Epidemiology
of infectious diseases
Kolářová M., EPI Autumn 2019
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Epidemiology
is the study of the:
occurrence,
frequency,
distribution and
causes of diseases
in a given population.
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In tracking a disease outbreak,
epidemiologists may use
any or all of three types of investigation:
a) descriptive epidemiology
b) analytical epidemiology,
c) experimental epidemiology.
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a) descriptive epidemiology
is the collection of all data describing
the occurrence of the disease,
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2. analytical epidemiology,
attempts to determine the cause
of an outbreak.
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c) experimental epidemiology
tests a hypothesis about a disease or
disease treatment in a group of
people.
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Epidemiologic investigations are
largely mathematical descriptions
of persons in groups, rather than
individuals.
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The basic quantitative
measurement in epidemiology is
a count of the number of persons
in the group being studied who
have a particular disease.
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Any description of a group suffering from a
particular disease must be put into the context of
the larger population.
This shows what proportion of the population
has the disease:
the prevalence rate refers to the total number
of cases of a disease in a given population at a
specific time.
the incidence rate refers to the number of new
cases of a disease in a population over a period
of time.
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Epidemiologists arrange their data in various ways,
depending on what aspect of the information they want
to emphasize.
One of the most powerful tools an
epidemiologist can use is case reporting:
reporting specific diseases to
* local,
* state and
* national health authorities,
who accumulate the data
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Modern infectious disease
epidemiology
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According to clasic definition,
epidemiology of infectious
disease
in its theoretical part
studies the chain of infections
(epidemic process)
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THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV, listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC, measles, influenza…)
- ingestion of food or water that is contaminated (salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
3. the susceptibility of the population or its individual members to the organism
concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. source of infection
……….
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the agent of infection (e.g., particular
bacterium or virus),
Organism characteristic:
infectivity – capacity to multiply in host
pathogenicity – capacity to cause disease in host
virulence - pathogenicity in a specific host
immunogenicity – capacity to induce specific and
lasting immunity in host
antigenic stability – can induce long-life immunity
resistance - in environment
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Organisms vary in their capacity to survive in the
free state and to withstand adverse
environmental conditions, for example:
* heat, cold, dryness.
Sporo-forming organisms, such as tetanus bacilli
which can survive for years in a dormant state,
have a major advantage over an organisms like
the gonococcus which survive for only a very
short time outside the human host.
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Slime-producing coagulase-negative staphylococci. Scanning electron micrograph of the
surface of an intravascular catheter incubated in vitro with (a) slime-producing and (b)
nonslime-producing strains of Staphylococcus epidermidis. With permission from
Christensen.9
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Staphylococcus aureus
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◼ Electron microscopy of group A streptococcus. The
fuzzy M protein layer can be seen protruding from
the cell wall..
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Obtained after an outbreak, this micrograph depicts Gram-positive
Clostridium difficile bacteria.
Source: CDC
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Under a moderately-high magnification of 8000X, this colorized scanning
electron micrograph (SEM) revealed the presence of a small grouping of Gramnegative
Salmonella typhimurium bacteria that had been isolated from a pure
culture. See PHIL 10986 for a black and white version of this image.
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Ziehl-Neelsen stain of 'cords' of Mycobacterium
tuberculosis isolated from a broth culture. Tubercle bacilli
aggregate end to end and side to side to form serpentine
cords, especially in broth cultures.
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Rotavirus
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HEPATITIS A VIRUS
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Sarcoptes scabiei
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Helical structure of Treponema pallidum with the
periplasmic flagella.
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Contamination of humans by micro-organisms.
Many parts of the body are colonized by normal flora,
which can be the source of endogenous infection.
Large numbers of micro-organisms are found in moist
areas of the skin (e.g. the groin, between the toes),
the upper respiratory tract, the digestive tract (e.g. the
mouth, the nasopharynx), the ileum and large
intestine, the anterior parts of the urethra and the
vagina.
Other routes are interhuman transmission of infections
and exposure to exogenous contamination.
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1. the presence of source of
infection
is the site or sites in which a disease agent normally lives and
reproduces.
May be classified as:
- human - at the ende incubation period,
if is ill,
reconvalescent,
carriers – healthy,
chronic diseases
- animals - at the ende incubation period,
if is ill,
carriers – healthy,
reconvalescent, chronic
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Staphylococcal nasal carriage. This patient had a small staphylococcal abscess beneath the
mucosa of the nose, illustrating how Staphylococcus aureus, which colonizes the nares, can
infect skin and submucosa. Intact mucosa is highly resistant to infection; such infections
usually occur as a result of defects in the mucosal membranes or via hair follicles inside the
nose.
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Septic pulmonary emboli. Multiple nodular pulmonary infiltrates secondary to a
dialysis catheter-associated infection. The patient presented with high fevers, cough
and pleuritic chest pain. Staphylococcus aureus was isolated from multiple blood
specimens.
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2. the metod of transmission
A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp.,
Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV,
listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC,
measles, influenza…)
- ingestion of food or water that is contaminated (salmonella,
giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
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Routes of transmission
➢ Air
➢ Food, Drink or Water
➢ Direct or indirect contact
* Transplacental
➢ Insects (Artropods)
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Main portals of entry
➢ Respiratory tract
➢ Gastro-intestinal tract
➢ Genito-urinary tract
➢ Direct break through skin
* surgical and wounds
➢ Direct into blood via needles/catheters
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3. the susceptibility of the population or its
individual member to the organism
concerned, and the characteristic of the
organism itself.
Host factors :
a g e - the very young and the very elderly are more susceptible to infetious
diseases than are older children and younger adults
n u t r i t i o n
g e n e t i c s
i m m u n i t y – natural, acquired and population
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Scarlatina (scarlet fever)
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Among the important environmental factors that affect
an epidemic of infectious diseases are:
poverty, overcrowding, lack of sanitation,
and such uncontrollable factors:
as the season and climate.
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➢ Impetigo in a child.
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Varicella (chickenpox)
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Varicella (chickenpox). Lesions at various stages, including
vesicles, can be seen.
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Typical rash of meningococcal septicemia. Fine
erythematous macules and petechiae are present in some
areas.
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Morbilli (Measles). A disseminated erythematous rash can be
seen over the trunk and arms.
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Rubella. A pink macular rash can be seen on the forearm.
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Rubella
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Primoinfection HIV
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Parotitis epidemica ( mumps)
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Scabies
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Crusted or Norwegian scabies in a patient who has AIDS.
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Lyme boreliosis (LB)
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LB - Typical erythema migrans rash.
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In the practical part it is preoccupied with
preventive measures
repressive measures
related to infectious diseases
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THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV, listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC, measles, influenza…)
- ingestion of food or water that is contaminated (salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
3. the susceptibility of the population or its individual members to the organism
concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. source of infection
……….
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If the epidemiology is know, we can
interfere with transmission:
„BREAKING THE CHAIN OF
INFECTION“
Different infections have different
epidemiologies and thus require different
methods of control
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THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
B/ indirect contact
3. the susceptibility of the population or its individual members to the organism
concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. source of infection
……….
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Prevention of infectious diseases
Isolation of patients:
- Dpt. of infectious diseases,
- „high degree of isolation“ (ebola)
- at home,
- barriers nursing technique
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
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Prevention of infectious diseases
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
HANDWASHING, DISINFECTION OF HANDS
LINEN WASHING,
CLEANING
GOOD PREPARING OF FOOD, SAFE
WATER……..,
………
DISINFECTION
STERILIZATION
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Prevention of infectious diseases
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
i m m u n i t y
– natural (nonspecific),
- acquired (vaccination)
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◼ The distribution of the
smallpox rash is
usually similar to that
shown here. It is
most dense on the
face, arms and hands,
legs and feet. The
trunk has fewer pocks
than the extremities.
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Smallpox is a disfiguring disease. Three out of ten cases may die. It is caused by variola
virus. The disease is spread by secretions from the patient's mouth and nose, and by material
from pocks or scabs. It is transmitted directly from one person to the next. Close contact with
patients, or their clothing or bedding, is thus required for infection. A patient who has
developed the distinctive symptoms of smallpox will have been exposed to the virus about two
weeks previously.
The 14 steps of an epidemic investigation
1. Confirm the existence of an epidemic.
2. Verify the diagnosis.
3. Develop a case definition.
4. Develop a case report form.
5. Count the cases (i.e., an approximate analysis).
6. Orient the data (i.e., time, place, and person).
7. Analyze the data (e.g., agent, transmission, and host).
8. Develop a hypothesis.
9. Test the hypothesis.
10.Plan and implement control and prevention measures.
11.Evaluate the implemented measures.
12.Establish or improve the public health surveillance.
13.Write a report.
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1. Respiratory tract infections
➢ Influenza
➢ Avian influenza and other animal influenzas
➢ Legionnaires’ disease
➢ Severe acute respiratory syndrome (SARS)
➢ Tuberculosis
2. Sexually transmitted infections, including HIV and
blood-borne viruses
❖ Chlamydia trachomatis infection
❖ Gonorrhoea
❖ Hepatitis B virus infection
❖ Hepatitis C virus infection
❖ HIV/AIDS
❖ Syphilis
3. Food- and waterborne diseases and zoonoses
➢ Anthrax
➢ Botulism
➢ Brucellosis
➢ Campylobacteriosis
➢ Cholera
➢ Cryptosporidiosis
➢ Echinococcosis (hydatid disease)
➢ Shiga toxin/verocytotoxin-producing Escherichia coli (STEC/VTEC)
infection
➢ Giardiasis
➢ Hepatitis A
➢ Leptospirosis
➢ Listeriosis
➢ Salmonellosis
➢ Shigellosis
➢ Toxoplasmosis (congenital)
➢ Trichinellosis
➢ Tularaemia
➢ Typhoid/paratyphoid fever
➢ Variant Creutzfeldt–Jakob disease (vCJD)
➢ Yersiniosis
4. Emerging and vector-borne diseases
❑ Malaria
❑ Plague (Yersinia pestis infection)
❑ Q fever
❑ Smallpox
❑ Viral haemorrhagic fevers
❑ Hantavirus
❑ Crimean–Congo haemorrhagic fever
❑ Dengue fever
❑ Rift Valley fever
❑ Ebola and Marburg virus
❑ Lassa fever
❑ Chikungunya fever
❑ West Nile fever
❑ Yellow fever
5. Vaccine-preventable diseases
✓ Diphtheria
✓ Invasive Haemophilus influenzae disease
✓ Invasive meningococcal disease
✓ Invasive pneumococcal disease
✓ Measles
✓ Mumps
✓ Pertussis
✓ Polio
✓ Rabies
✓ Rubella
✓ Tetanus
6. Antimicrobial-resistant pathogens and healthcareassociated
infections
o Antimicrobial resistance
o Antimicrobial consumption
o Healthcare-associated infections - HAI
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◼ b-Hemolytic streptococci group A on a blood agar plate.
Note the clear b-hemolytic zone.
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Erysipelas. Note the sharp demarcation of the
affected skin.
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◼ Necrotizing fasciitis caused by group A strepococci.
There is only moderate erythema but at surgery there
was extensive soft tissue damage.
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Mixed culture of two morphotypes of Enterobacteriaceae
on blood agar plate (Escherichia coli and Salmonella spp.).
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Pseudomonas aeruginosa monotrichous polar flagellum
seen on electron microscopy.
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Burned leg that has been superinfected with Pseudomonas
aeruginosa.
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Cultured Helicobacter pylori in coccoid and bacilli forms,
bound to immunomagnetic beads.
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Secondary syphilis with typical skin rash.
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Gonococcal urethritis.
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Colonies of Nocardia asteroides showing smooth chalkywhite
appearance.
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Primary cutaneous nocardial infection is characteristically painless, localized
and slowly progressive. (a) There is marked swelling and erythema in this
child's finger. (b) However, because the finger was painless the child was not
brought to medical attention until the infection had progressed to involve the
entire finger.
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Giemsa stain of blood with Borellia burgdorferi.
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Tick - Ixodes ricinus
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A blood-engorged female Aedes albopictus mosquito feeding on a
human host.
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Francisella tularensis
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Tularemia
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Tularemia
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Hlístice Trichinella spiralis
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Pathogenesis of rabies.
Headlines
Human cases of Q fever associated with ‘fresh cell therapy’
➢ 16 Oct 2015
➢ ​A new rapid risk assessment has been published on the risk of Q fever
associated with ‘fresh cell therapy’ following seven such cases being reported
in Germany.
➢ Six human cases of Q fever were associated with so-called ‘fresh cell
therapy’ performed in Germany in May 2014. These cases reconfirm the risk
of infectious disease transmission through xenotransplantation.
➢ The potential recipients of fresh cell therapy or other products of animal
origin, should be informed of the risks. Organisations that are active in
donation and transplantation of substances of human origin should be aware
that instances of fresh cell therapy occur, because potential donors who have
received animal cells as part of such therapy should be rejected for donation.
A number of European countries are in the process of regulating the practice
and others may consider also doing so by, for example, establishing national
systems for monitoring and traceability of xenotransplantation.
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➢ Fresh cell therapy despite unproven efficacy and numerous associated
risks, continues to be offered and used. Fresh cells are usually isolated
from the homogenised organs and tissues of sheep foetuses and
placentas, The live cells or extracts are injected into the recipient in order
to obtain a purported revitalising effect. Often, these therapies are
promoted as anti-aging treatments, treatment for chronic diseases, agerelated
disorders (such as arteriosclerosis) or as an alternative treatment
for cancer.
➢ Q fever is an infectious disease caused by bacteria called Coxiella
burnetii that affects both humans and animals. Q fever can be a mild
illness but symptoms include sudden headaches, fever, chills, muscle
soreness and, in some cases, pneumonia. Some symptoms such as
fatigue can be long-lasting.
➢ Complications
➢ In a very small number of cases (around 1%), Q fever leads to a more
serious illness known as chronic Q fever, sometimes after a number of
years. The most common symptom of chronic Q fever is inflammation of
the inner lining of the heart (endocarditis), which can be deadly if not
treated.
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