1
Introduction to infectious diseases
epidemiology
Three parts of the chain of infections´ dissemination; their role
in the primary prevention of infectious diseases
aBFEP051p – October 16, 2021
Kolářová M., mkolar@med.muni.cz
165 -190 A.D. ANTONINE SMALLPOX PLAQUE 5 mil. death
541 – 542 PLAQUE OF JUSTINIAN Yersinia pestis 2 mil. death
Pre-host rats, fleas
735 – 737 JAPANESE SMALLPOX EPIDEMIC Variola major virus 2 mil. death
1347 – 1351 BLACK DEATH Yersinia pestis 2 mil. death
1520 -----------1980 NEW WORLD OUTBREAK Variola major virus 56 mil. death
………………………………………….
1980 ERADIKACE NEŠTOVIC
Historical overview
1629 -1631 ITALIAN PLAQUE Yersinia pestis 1 mil. death
1817 – 1824 CHOLERA PANDEMICS Vibrio cholerae 1 mil. death
1885 THIRD PLAQUE Yersinia pestis 12 mil. death
………………. ……………
Late 1800s YELOW FEVER Yelow fever virus 100 000 – 150 000
death
1889-1890 RUSSIAN FLU H2N2; Pre-host - avian origin 1 mil. death
1918 – 1919 SPANISH FLU H1N1; Pre-host -pigs 40 – 50 mil. death
…………………......
1957 -1958 ASIAN FLU H2N2; Pre-host – avian origin 1 – 2 mil. death
1968 - 1970 HONG-KONG FLU H3N2 1 mil. death
1980 ----------- present HIV/AIDS 36 mil. death
………………………………………….
2002-2003 SARS (Severe Acute Respiratory Syndrome) Coronavirus 770 death
Pre-host bats, civests
2009 – 2010 SWINE FLU 200 000 death
2014 -2016 EBOLA 11 000 death
2014 --- present MERS (MERS-CoV – Middle East Respiratory Syndrome Coronavirus) 866 death
2019 -- present COVID 19
……… 30 mil. infections/1 mil. death
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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
(collection of all date describing the occurence of the disease)
b) analytical epidemiology
(attempts to determine the cause of an outbreak)
c) experimental epidemiology
(tests a hypothesis about a disease or disease treatment or prevention
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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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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Varicella (chickenpox)
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Varicella (chickenpox). Lesions at various stages, including
vesicles, can be seen.
14
Erysipelas. Note the sharp demarcation of the
affected skin.
15
Scarlatina (scarlet fever)
16
➢ Impetigo in a child.
17
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.
18
Typical rash of meningococcal septicemia. Fine erythematous
macules and petechiae are present in some areas.
19
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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Parotitis epidemica ( mumps)
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Primoinfection HIV
24
Secondary syphilis with typical skin rash.
25
Gonococcal urethritis.
26
Lyme boreliosis (LB)
27
LB - Typical erythema migrans rash.
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Scabies
29
Crusted or Norwegian scabies in a patient who has AIDS.
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Tularemia
31
Tularemia
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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 CAUSATIVE AGENT OF INFECTION
(bacteria, viruses, fungi, prions, protozoa)
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
36
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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◼ b-Hemolytic streptococci group A on a blood agar plate.
Note the clear b-hemolytic zone.
39
◼ Electron microscopy of group A streptococcus. The
fuzzy M protein layer can be seen protruding from
the cell wall..
40
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.
41
Mixed culture of two morphotypes of Enterobacteriaceae
on blood agar plate (Escherichia coli and Salmonella spp.).
42
Pseudomonas aeruginosa monotrichous polar flagellum
seen on electron microscopy.
43
Cultured Helicobacter pylori in coccoid and bacilli forms,
bound to immunomagnetic beads.
44
Obtained after an outbreak, this micrograph depicts Gram-positive
Clostridium difficile bacteria.
Source: CDC
45
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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Rotavirus
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HEPATITIS A VIRUS
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50
Helical structure of Treponema pallidum with the
periplasmic flagella.
51
Sarcoptes scabiei
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Giemsa stain of blood with Borellia burgdorferi.
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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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Colonization 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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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
58
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 - 1. at the ende incubation period,
2. if is ill,
3. after acute stage –
* reconvalescent,
* carriers – healthy,
* chronic diseases
- animals - at the same situation
60
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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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….)
The rise of the pandemic strain
Interhuman transmission ?
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Tick - Ixodes ricinus
65
A blood-engorged female Aedes albopictus mosquito feeding on a
human host.
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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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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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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, specific),
- acquired (after vaccination)
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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ANTI - EPIDEMIC MEASURES
1. the presence of rezervoir (source) of infection
ISOLATION
2. the way of transmission HAND WASHING, LINEN WASHING, CLEANING,
GOOD PREPARING OF FOOD, SAFE WATER……..,
DISINFECTION, STERILIZATION
3. the susceptibility of the population or its individual member
to the organism concerned VACCINATION
THE INFECTION
= 1. source of infection
. . . . .
X
x
XREDUCING THE INCIDENCE,
ELIMINATION,
ERADICATION
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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.
Remembering an Old Disease
Smallpox
Face lesions on boy with smallpox.
Public Health Images Library (PHIL) ID # 3.
Source: CDC/Cheryl Tyron
Smallpox recognition
card, c.1973, courtesy
Dr. Damodar Bhonsule,
Panjim, Goa, India.
Smallpox lesions on skin of trunk.
Picture taken in Bangladesh, 1973.
Public Health Images Library (PHIL) ID # 284. Source: CDC/James Hicks
Rural vaccinator in United Provinces, British India, c.1930, private collection of Dr. Sanjoy Bhattacharya
Variola virus, which causes smallpox, was once the scourge of the world.
This virus passes from person to person through the air.
A smallpox infection results in fever, severe aches and pains, scarring
sores that cover the body, blindness in many cases, and, often, death.
There is no effective treatment.
Although vaccination and outbreak control eliminated smallpox in the
United States by 1949, the disease still struck an estimated 50 million
people worldwide each year during the 1950s.
In 1967, the World Health Organization (WHO) launched a massive
vaccination campaign to rid the world of smallpox —and succeeded.
The last natural case of smallpox occurred in Somalia in 1977.
Ali Maow Maalin, cook twenty-three of the hospitals in the Somali Merce.
He contracted when he showed the path of the ambulance chauffeur who drove
two sick children to camp insulation.
In 1978 was ill photographer Medical School in Birmingham, England. She was killed
by a virus that escaped from a neighboring lab.
Mr. John Wickett, of the World Health Organization,
with the last person to have contracted – and survived –
naturally occurring smallpox in Somalia.
(1977), courtesy Mr. John Wickett.
Eradication of smallpox
Czech experts
A key figure in the global eradication program
smallpox was prof. MUDr. Karel Raska, MD.,
who drove in the sixties division
Communicative Diseases of the WHO
Secretariat in Geneva.
He promoted the establishment of a new, independent units
"Eradication of smallpox"and ensure its initial financial and
material support, not only in Geneva,
but also in regional offices of WHO.
With its support of the program also attended the 20
Czechoslovak health professionals (14 Czechs and Slovaks
6), mainly epidemiologists.
They participated in both the preparation methodology and
procedures, thus working directly in infested areas.
Smallpox eradication was
officially announced
at the 33rd General Assembly WHO
8. May 1980.
Tuesday, March 8, 2011; 9:41 AM
Milestones in the eradication of smallpox
1789 Edward Jenner invents a smallpox vaccine.
1966 The World Health Organization (WHO) launches a massive global
campaign to eradicate smallpox.
1972 Smallpox vaccinations are discontinued in the United States.
1975 and 1977 The last cases of the two known variants of smallpox occur in
the world, in Bangladesh and Somalia.
1978 Two people are sickened in a lab accident in England; one dies.
1980 The WHO declares smallpox eradicated.
1991 Smallpox virus DNA is mapped.
1999 The WHO sets this deadline, by which remaining lab stocks of the virus are to
be destroyed. The deadline will be postponed again and again.
2003 Millions of doses of vaccine are produced to hedge against a biological
attack.
2011 WHO's decision-making body will meet in May to again vote on whether to kill
the remaining live viruses.
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In the practical part it is preoccupied with
preventive measures
repressive measures
related to infectious diseases
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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Infections by route of transmission
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 bloodborne
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