1
Epidemiology
of infectious diseases
Kolářová M., EPI Autumn 2019
EPIDEMIOLOGY
is the study (scientific, systematic, data-driven)
of the distribution (frequency, pattern)
and determinants (causes, risk factors)
of health-related states or events (not just diseases)
in specified populations (patient is community,
individuals viewed collectively),
and the application (since epidemiology is a discipline
within public health) of this study to the control of health
problems.
2
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In tracking a disease outbreak, epidemiologists may
use any or all of three types of investigation:
a) descriptive epidemiology
is the collection of all data describing the occurrence 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 in a group
of people.
◼ Incidence - the incidence rate refers to the number of new
cases of a disease in a given population over a period of time.
◼ Prevalence - the prevalence rate refers to the number of total
cases of a disease in a given population at a specific time.
◼ Sporadic disease Disease that occurs
occasionally in a population.
◼ Endemic disease Disease constantly present in a
population.
◼ Epidemic disease Disease acquired by many
hosts in a given area in a short
time.
◼ Pandemic disease Worldwide epidemic.
Occurrence of Disease
5
Epidemiologic investigations are
largely mathematical
descriptions of persons in groups,
rather than individuals.
6
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
7
Modern infectious disease
epidemiology
0
10000
20000
30000
40000
50000
60000
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
0
10000
20000
30000
40000
50000
60000
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Varicella
10
Varicella (chickenpox)
11
Varicella (chickenpox). Lesions at various stages, including
vesicles, can be seen.
0
10000
20000
30000
40000
50000
60000
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Plané neštovice
Salmonelóza
0
10000
20000
30000
40000
50000
60000
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Varicella
Kampylobakteriosis
Salmonelosis
0
10000
20000
30000
40000
50000
60000
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Varicella
Kampylobakterióza
Salmonelóza
231,7/100 000
111,3/100 000
490,4/100 000
0
200
400
600
800
1000
1200
1400
1600
1800
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
VHA 15,8/100 000
VHC 10,4/100 000
VHB 0,8/100 000
VHE 3,9/100
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➢ 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
Staphylococcus aureus
19
Scarlatina (scarlet fever)
20
➢ Necrotizing fasciitis caused by group A strepococci.
There is only moderate erythema but at surgery there
was extensive soft tissue damage.
21
➢ b-Hemolytic streptococci group A on a blood agar plate.
Note the clear b-hemolytic zone.
22
➢ Electron microscopy of group A streptococcus. The
fuzzy M protein layer can be seen protruding from
the cell wall..
23
Typical rash of meningococcal septicemia. Fine erythematous
macules and petechiae are present in some areas.
24
Morbilli (Measles). A disseminated erythematous rash can be
seen over the trunk and arms.
0
50
100
150
200
250
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Spalničky
26
Rubella. A pink macular rash can be seen on the forearm.
27
Rubella
28
Parotitis epidemica ( mumps)
29
Scabies
30
Crusted or Norwegian scabies in a patient who has AIDS.
31
Sarcoptes scabiei
32
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Gonococcal urethritis.
0
200
400
600
800
1000
1200
1400
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
Název grafu
Gonokokové infekce
11,1/100 000
Syfilis
9,7/100 000
35
Secondary syphilis with typical skin rash.
36
Helical structure of Treponema pallidum with the periplasmic
flagella.
37
Primoinfection HIV
TB notification rates per 100 000 population by year
of reporting, EU/EEA, 1995-2016
11,4/100 000
0
500
1000
1500
2000
2500
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Tuberkulóza
2 079 případů = 20,2/100 000
505 případů = 4,9/100 000
TBC – in Slovakia - 2013
number of cases/100 000 residents
16,15
8,06
4,81
4,79
4,89
4,31
5,71
BA TT
TN
NI
ZA
BB
5,62
PO
KE
Source: Doc. MUDr. Ivan Solovič, CSc.
Poliomyelitis
Morbid changes occur
mainly in the gray matter of the spinal cord.
The infectious agent:
There are three types of polioviruses
-1, 2 and 3.
Virus excretion: 1 week from the nasopharynx,
6 weeks of stool.
80% of cases are asymptomatic.
• Polio Viruses, which are endemic or epidemic areas
• spreading in a population,we are known as wild polioviruses.
• Among them were for the purpose of preparing
live vaccines repeated passaging the virus in cell cultures
resulting strain called vaccinal.
Polio this week as of 02 October 2019
• September’s Polio News is now available with the latest polio numbers and
news updates.
• Summary of new viruses (AFP cases and ES positives) this week:
• Pakistan— three WPV1 cases and 13 WPV1-positive environmental samples;
• the Democratic Republic of the Congo— one circulating vaccine-derived
poliovirus type 2 (cVDPV2) case;
• Ghana— one cVDPV2 case and five positive environmental samples;
• Philippines— one cVDPV2 case, one cVDPV2 and 5 cVDPV1 positive
environmental samples.
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Polio eradication
In 1988, the forty-first World Health Assembly adopted a resolution for the worldwide eradication of polio, the
Global Polio Eradication Initiative (GPEI). Since then, the number of cases has fallen by over 99% from an
estimated 350 000 to 416 reported cases in 2013.
In 2014, only three countries in the world remained polio-endemic: Nigeria, Pakistan and Afghanistan.
In 2015 to date, two countries have together reported 37 cases: Pakistan (29 cases) and Afghanistan (eight cases),
all due to wild poliovirus type 1.
The last natural circulation of WPV2 was in India in 1999 and the last WPV3 case was detected in Nigeria in
November 2012.
• Since then, WPV1 has been the only circulating wild type virus.
The last case of endemic paralytic polio in the WHO European Region (i.e. with the source of the infection
originating in the Region) was reported in Turkey in November 1998,
and the Region was declared polio-free in June 2002.
The most recent outbreaks linked to importations into the WHO European Region occurred in 2010 in Tajikistan
and in 2013–2014 in Israel where WPV1 was circulating in the environment without causing clinical cases .
The most recent polio outbreaks in what today constitutes EU/EEA were in the Netherlands in 1992, in a religious
community opposed to vaccination,
and in 2001, when three polio cases were reported among Roma children in Bulgaria .
On 5 May 2014, WHO declared the international spread of wild poliovirus in 2014 a Public Health Emergency of
International Concern (PHEIC) following the confirmed circulation of wild poliovirus in several countries and the
documented exportation of wild poliovirus to other countries.
The Polio Eradication and Endgame Strategic Plan 2013–2018 sets out the actions required for a polio-free world
by 2018 and beyond.
47
Burned leg that has been superinfected with Pseudomonas
aeruginosa.
48
Pseudomonas aeruginosa monotrichous polar flagellum seen
on electron microscopy.
49
Lyme boreliosis (LB)
50
LB - Typical erythema migrans rash.
51
Giemsa stain of blood with Borellia burgdorferi.
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Tick - Ixodes ricinus
53
Colonisation and 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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Infectious diseases result from the interaction of
agent, host, and environment.
More specifically - spreding of infections occurs when:
the agent leaves its 1.reservoirs or host (source) trough a portal of exit,
is conveyed 2.by some mode of transmissin
and enters trough an appropriate portal of entry to infect
3.a susceptible host.
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THE CAUSATIVE AGENT OF INFECTION
(viruses, Chlamydia, rickettsia, mycoplasma, spirochete, bacteria, prions, fungi, protozoa helminthes)
1. the presence of rezervoir (source) of infection
2. the way of transmission
3. the susceptibility of the population or its individual member
to the organism concerned
THE INFECTION
= 1. source of infection
. . . .
. .
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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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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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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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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 :
Non specific immunity
Barrier action (natural barrier)
External barrier:
skin , mucosa
Secretion of skin and mucosa
Accessory organ
Internal barrier: placenta, blood-brain barrier
Phagocytosis
Humoral action :
Complement, Lysozyme, Fibronection, Cytokines.
Specific immunity
Humoral immunity
Immunoglobulin: IgG, IgM, IgE, IgA, IgD
Cell mediated immunity
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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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THE CAUSATIVE AGENT OF INFECTION
(viruses, Chlamydia, rickettsia, mycoplasma, spirochete, bacteria, prions, fungi, protozoa helminthes)
1. the presence of rezervoir (source) of infection
2. the way of transmission
3. the susceptibility of the population or its individual member
to the organism concerned
THE INFECTION
= 1. source of infection
. . . .
. .
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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
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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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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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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