Download Epidemiology: it is the science that deals with studying the

Epidemiology: it is the science that deals with studying the occurrence
and distribution of health and disease in human population
Epi= upon
Dem= people
Ology= science or knowledge
* Epidemiology is categorized into: demography (people population)
statistical epidemiology and preventive epidemiology.
* Preventive epidemiology deals with the studying factors which
determine disease occurrence. For a disease to occur three factors must be
present and interact with each other. These factors may be:
1. Intrinsic (internal) e.g. agent (A), host (H).
2. Extrinsic (external) e.g. environment.
Agent (A):
Agents the true case of the desase without it which a specific disease
cannot occur
* Examples of the agents are:
1. Microorganism as bacteria, viruses
2. Chemical substance (agent):*poisons as exposure to Co.
* Allergens as medical products.
3. Physical agents as radiation, excessive cold or heat.
4. Exposure for carcinogenic substances as the case when eating outdated
food or frying food frequently boiled oil.
5. Nutritional disturbances as when a child is eating too much
carbohydrate and lees protein will develop kwashiorkor. Or in eating
cholesterol rich diet ---------- cholesterolemia
Vitamin deficiency decrease ------ ricket
* Agents has certain properties that determine the mechanism of
disease transmission, its morbidity (ability to cause disease or
mortality (ability to cause death)
* Factors determine the effect of an agent: properties
1. Resistance: its ability to survive in a free state to resist
temperature, light, other influences.
2. Viability: it is ability to multiply outside human body e.g.
bacteria can multiply in non living media such as food and milk.
But viruses can multiply within living cells.
3. Invasiveness, virulence and pathogenicity: its ability to cause the
disease, some viruses is very virulent (strong) e.g. poliomyelitis,
other are not (weak) e.g. common cold viruses.
4. Effective dose, duration.
5. Host specificity
Host (H):
This is the person susceptible to illness. Host may be human or non
human
* factors which affect and Control the host
1. Age (some disease are age – related as poliomyelitis)
2. Sex (cancer cervix)
3. Race or ethnic factor (black more susceptible for
hypertension)
4. Genetic (sickle cell anemia, thalassemia)
5. Resistance (man is immune against avian tuberculosis)
6. Behavior, life style, diet, personal hygiene, contact with other
person food handling.
Environment (E)
Factors external to the agent or host.
*types of environmental factors
1. Physical: climate (heat, cold) air (pollution), water
(pollution), radiation.
2. Socioeconomic: social status (crowding area without
ventilation, diet) occupation e.g. exposure to chemical agents,
wars, famine, floods, urbanization. Health education
3. Biological: infectious agent's disease, reservoir of infection,
mode of transmission by flies, mosquitoes, air.
*distribution of the disease involves the study of:
1. Person (age, sex, nationality, marital status, social class,
occupation, education).
2. Place: rural, urban, national, international.
3. Time: epidemic, cyclic, seasonal.
Preventive epidemiology
* Epidemiology is dealing with mans status in health and
disease
* If we talk about health we mean mental, physical, social and
psychological well being, we don’t mean absence of disease
only
* Preventive epidemiology: is dealing with how to prevent
disease occurrence and promote good health.
*disease may be: 1. Acute, communicable e.g. cholera
2. Chronic, non- communicable e.g.
Hypertension
1. Acute, communicable, disease:
Is a disease caused by a specific infectious agent (living agent)
or its toxic products.
* Infectious agent is transmitted from a reservoir to a
susceptible host.
Type of transmission: a) direct from infected person or animal.
b) Indirect from intermediate host or
environment.
Incubation period: short (hr, days, weeks)
Etiology: monofactorial agent e.g. bacteria, viruses, fungus.
Cure: usually by medical treatments and certain possible
prevention and control for infectious disease
2. Chronic, non- communicable, disease:
It arises as a result of exposure to certain specific agent that
causes specific disease.
Type of agents: chemical, gases, radiation, allergens
Incubation period: long (months, years)
Etiology: multifactorial.
Cure: usually persist for long time and the majority of them
terminate with death of patient.
Transmission of diseases:
Mechanism of disease transmission:
There are 3 actions (step) for disease transmission:
1. Escape of the agent from the source or reservoir
2. Conveyance of the agent to a susceptible host.
* There are 2 ways of conveyance of agent to susceptible
host
A.)Direct, immediate, where no vectors is involved from
person to person through actual physical contact i.e.
transmission through direct contact between susceptible
host and reservoir (infected person, e.g. gonorrhea,
syphilis.
B.) indirect: involve the use of vector as:
1.) Animate (living e.g. blood sucking arthropod),
transmission occur after incubation period during which
agent multiplies in the arthropod vector.
2.) Inanimate (non- living) which facilitate indirect
transmission e.g. personal articles as keys, pens.
3. Entry through appropriate entry point
Portal of entry:
The path by which infectious agent enter the susceptible
host e.g. respiratory, gastrointestinal.
Portal of exit:
This is the pathway through which infectious agent
leaves the reservoir.
e.g. respiratory : (coughing, sneezing, talking)
- genitourinary: (Foley catheter, sexual transmitted
disease)
- skin, mucus membrane :( wounds, skin breaks, needle
sticks, blood transfusion).
- vertical e.g. :( transplacental transmission).
Type of
disease
Cold
Site of
entry
respiratory
tract
measles
common
serum
hepatits
malaria
Mode of transmission
inhalation of by
infectios
exit
respiratoty
secration
Droplets of
infectious
agent
skin
Intravenous (I.V) or
subcutaneous inoculation
skin broken mosquito sucking infected
insect by
bite
gonorrhea
genital
Person sexual intercourse
syphilis
mucous
person ot
membrane
Typhoid
G.I.T
By ingestion of infected
fever
water, food
Diphtheria
Person To person by
tuberculosis Upper
inhalation of infected
(T.B)
respiratory droplets
tract
* Person to person or serial transfer transmission:
Def: the spread of a disease agent through contact
between infection and susceptible persons.
Examples of disease: measles, syphilis, gonorrhea.
blood
blood
infected
exudates
(stool)
faeces
respiratory
secration
*mode of transmission
The mechanism of transfer of an infective agent from the
reservoir to a susceptible host.
1. Air –born. (Droplet infection) respiratory system.
Organism contained within droplet nuclei or dust
particles. (Droplet nuclei of tuberculosis).
For example if the agents viral in origin affecting the respiratory tract,
e.g. measles, rubella, whooping cough, mumps
If the agent is bacteria in origin e.g. tuberculosis, diphtheria, sore throat
(streptococcus)
2. faeco-oral (gastrointestinal) transmission:
The source is usually contaminated food (milk,
water).flies and fingers are potent routes for
transmission.
Agent is mostly bacterial in origin e.g. typhoid fever,
cholera, bacillary dysentery.
It may also be protozoa or amoebic e.g. amoebic
dysentery.
3. Sexually transmitted (venereal) disease (STDS):
It occurs by closely body contact because agent is
usually killed outside the body e.g. gonorrhea,
syphilis, AIDS.
4. Contact transmission (other than STDs):
this occur through direct contact through skin or
mucus membrane.
Examples: 1) some dermatological disorders (tenea
vercicolor, herpes simplex by kissing)
2) Eye infection e.g. trachoma by flies or
contaminated finger or towels
5. animal transmitted diseases (zoonoses):
Where an animal is the mode of transmission.
Example: intestinal T.B. by ingestion of row milk
contaminated by bovine T.B.
6. Insect –borne disease (vector- born):
Examples:
1.) Malaria is protozoa diseases where the
parasite multiplies inside the body of the mosquito to
be mosquito bite.
2.) Yellow fever viruses .external vectorborn transmission by mechanical transfer on external
appendages (feet of flies), so the insect play an
essential role in disease transmission.
7. Vertical transmission:
It occur by transmission of infectious disease from
mother (one generation )to an infant (next
generation).
During:
A) Pregnancy (through transplacental way e.g. rubella in the first three
months of pregnancy)
B.)Delivery (through infection e.g. toxoplasmosis, cytomegalovirus)
C.) Breast feeding
*transmission of HIV from mother passes to the baby:
1. during pregnancy through placenta.
2. during delivery through process contact.
3. after delivery through breast feeding
*person to person
_disease agent is transmitted through contact between infected and
susceptible person.
_can spread by means of respiratory, anal, oral, genital routes.
viral Transmitted infection
HIV
Hepatits B
Genital herps
Genital warts
Rubella
Cytomegalovirus
bacteria Transmitted disease
chlamidia
gonrrhea
bacterial vaginitus
trichomoniasis
syphilis
investigation of epidemices
Infectious disease e.g. cholera , typhoid are common in developing
tropical countries. Epidemics are caused also by diseases other than
infectious diseases e.g. chemical food contamination air pollution , lung
cancer.
Steps of investigation of epidemics:
1)confirmation of the diagnosis by clinical and laboratory method.
Aims: A.)to determine the correct cause of epidemic disease for
examples. To differential diagnosis between hepatitis and yellow fever.
The both diseases have the jaundice (yellowish colorations of the eye)
*differential diagnosis between cholera and food poisoning.
*differential diagnosis between meningitis and encephalitis.
B.)to confirm the diagnosis of the cause of the death of the cases.
2)Confirmation the existence of an epidemics by presence of large
number of person which have the same complaints of the same case.
3) description of epidemics:
It means the identification of affected persons and their characteristic
A)with respect to time : it is done by plotting the cases by the time of the
onset of symptom using the epidemics curve .
*Epidemics curve
Incubation period (I.P): It is the time (minutes, hours, days, months, or
even years) between the exposure to agent and the onset of symptomes
and sings of the disease.
Symptoms:are the complaints of patient by his or her words.
Signs: are the objective findings which are seen by doctors, nursing or
paramedicans.
Use of I.P.:
1. Determine the source of infection: for example; small pox the patient
couid be asked about the movments and contacts with persons. 7-21
dayes befor he got sick
2.determine the period of expouser to contacts:it means the period time
equal to the usually incubation period of the infection agent.
3. immunization: certain disease can be prevented by immunization in
incubation period.
For example: with immunoglobulin (Ig)can be prevented or modify an
attack of measles in child which contact with infection.
4. prognosis: in some infection, the prognosis is related to incubation
period .the shorter I.P, the worse prognosis e.g. tetanus
Factor that determine the epidemics:
1. onset of the disease.
2. the specific disease which is characterized by its I.P.
3. the time of exposure to the etiological agent.
B. With respect to place:
It is done plotting the cases by the location of the part of city which they
come from using spot map.
In use of spotmap, case location can by place of residence, place of work
or school attended.
A
C
C. With respect to person:
B
D
It is done by tabulating the distribution of cases by age ,sex, nationality
,occupation, religion, and other characters.
Aims: to determine the pin-pointing the exact population at risk.
4. determine of individual epidemics histories:
Aim: to allow the classification of exposed persons as to the following.
a. source of the infection
b. whether ill or not ill
c. if ill what is the clinical data, laboratory investigations
(results)which help to diagnosis of case.
A.) case history:
So, take details of each confirmed or suspected cases to obtain
complete picture of the epidemic. It include the following .age,
sex, name, occupation, place of residence, recent movement,
onset of disease, symptoms and sings of disease.
B.) Search of additional cases.
5. study of the environmental condition in the identified
place
e.g. investigation source, method of food preparation and
preservation in the area of restaurants.
6. study of source of infection and spread of epidemic
This can be done by comparing the percentage of persons
exposed to the suspected source or mode of infection among
those ill and those not ill.
The investigator doctor shouid be know why the epidemic
occurred and how the stage come to be set for its occurrence.
-In dry months, human movment may be increase the spread of
the disease such as meningococcal meningitisand influenza may
be facilitated.
-At other times, seasonak changes in the temperature and
humidity at night facilitate transmission of respiratory
organisms among persons sleeping at the room.
-Food supplies or water supplies or housing and sanitation
should be investigation and local health inspector who has some
knowledge of the area is usful person to have on the
investigation team.
- as regard to infectious process should be know on the
following:
1) the agent of disease and its characteristics.
2)the reservoir (man as a case , or carrier, animals,
insects,birds, plants, water or soil).
3. the mode of transmission to the next host.
4. the mode of exit from this reservoir or source.
5. the mode of entery.
6. the susceptibility of the host.
7)mangment of the epidemics: it include the following:
a. treatment of cases.
The doctor who investigation as an epidemic must also
responsibility for treatment of the cases he diagnosis.
e.g. in an epidemic of meningitis , plague or cholera need
emergency care with rapidly well training additional staff.
b. prevention of spread and control measures to plane a
complete control program.
☺many epidemic diseases can be prevented by:
Method of prevention of epidemic
a. immunization
b. isolation of affected individuals and imposition of
quarantine to prevent movement in or out of an area.
c. improvement of health hygiene through health
education
d. providing a better water supplies.
e. control of vector breeding or killing of vectors
f. long term plans for continued vaccination after an
initial mass programmed.
c. writing a report:
it is usual to write reports after investigation of an epidemic
type writing reports:
1.popular account for laymen.
Aims :a)to understand the nature of epidemic
b) to know the method to prevent spread or
recurrence.
2. an account for planners in the ministry of health.
Aims: to know the necessary steps are taken to limit the
outbreak or prevent recurrent.
3. scientific report
Aim: to teaching amedical staff about medical control.
- during the acute phase of epidemic, it is necessary to
keep the ondividual at special risk (e.g. contact) under
the surveillance.
- after the epidemic is under conrol, it is necessary to
keep the immunity under surveillance to detect further
rises in incidence or to insure effective control measure
-keep all links of chain (infectious agent, reservoir,
mode of transmission and level of immunity )under the
close observation.
-sources of information for surveillance:
1. notification of illness by medical staff, school
teachers or heads of families
2. certification of death by medical aurthrities.
3. data from other source e.g. public health
laboratories.
☺morbidity and mortality measures
They reflect the frequency of sickness producing and
death causing diseases in the community.
-Disease rate: it is the number of persons with a
disease per unit of the population of the place interest at
agiven time.
Disease rate = N/N+F*100
N :number of person having disease
F: Noumber of persons without disease
N &N+F come from same population
Morbidity: the frequency of illness in a socity
Mortality: the frequency of death in a society
*morbidity rate
Definition: it is the ratio of sick to well person in a society.
*aim for keeping morbidity rate:
1. help to control infectious or communicable disease by health agencies .
2. to make public program for planning and evolution proposes such as
center for retarded children.
3. to determine the effect of morbidity of workers in various industries.
4. for investigation causes of disease.
*source of morbidity records
1. disease control activates e.g. tumor registers.
2.goverment financial public assistance.
3. from data accumulated e.g. by routine hospital and health center
4. from morbidity survy
5.recordes o industrial and school absenteeism
*errors affecting morbidity and mortality data:
1. diagnostic inaccuracy.
2. incomplete identification of cases.
3. variability of the recording system.
4. population migration
5. change in population structure (age, sex, race………….)
6. change in administrative boundaries related to health serves.
*Incidence rate :number of new cases of disease that occur during a
specific period in a define population
Incidence rate = no. of new cases of disease in population during a
specific time ÷ no of persons exposed to the risk of developing of disease
during the same period *100%
* prevalence rate: no. of case in a defined population at a particular
point in time or during a specified period
Prevalence rate = no. of total cases (old &new) of disease present in
population at a specific time ÷ no. of persons in population at the same
specific time *100%
Attack rate =no. of total cases (old &new )on one day ÷ no. of actively
exposed persons *100%
Infant mortality rate = no. of death infants under 1 year during a period ÷
no. of live birth during same period*100%
Neonatal mortality rate= no. of death infants under 28days during 1
month period ÷ no. of live birth during same period*100%
Fertility rate= no of live birth in an area during a year ÷ midyear
population aged (15-44)in the same area, in the same age.*100%
Type of human reservoir casing spread of infection in the
community:
1.carrier
Is well person without appearance sings of disease and move freely
among the peoples.so, the carrier help the spread of infection.
2. subclinical sick individual:
A person has a mild sickness which unable to move about freely
3. frank sick individual (patient):
A person has clinical feature of disease without ability to movment.
So , it is isolated or hospitalized without chance to contact with
well person.
*control and prevention of infectious disease:
1. control the source of infection.
2. control channels of transmission.
3. protecting susceptible individual.
1. control the source of infection:
First, types sources (reservoir)of infection may be:
*general measures of control source of infection:
1. early diagnosis: ensure early detection before epidemic
transmission.
2. notification :help public health staff to immediate action to
efficient control.
3. isolation: limiting the spread of disease examples of disease need
isolation cholera, small pox.
4. treatment a.)reduce the infectious disease
b.) prevent the spread of disease
c.) prevent development secondary cases.
5. quarantine: is the detention of well person or contacts to come in
contact with infectious disease
the period of quarantine equal the longest incubation period of the
*disease
* it is important in the case of international travelers.
*common incubation period – cholera :5 days
_ plaque :6 days
_ yellow fever: 6 days
6. surveillance :
*during acute phase of an epidemic
Keep the community
under surveillance to detect further increase (rise)in incidence and
to ensure the effectiveness of selected control measures.
* best method for surveillance keep all links of chains.
a.)agents
b.)reservoir
c.)mode of transmission
d.)level of immunity
7. disinfection :should be performed on a.)concurrent level
b.)terminal level
a.)concurrent disinfection: def. means immediate destruction of
infectious material e.g. faecal material, urine, sputum
2. interruption or blocking channel of transmission:
methodes of transmission of infectious disease:
1.air borne infection:
*ways (method) of infection
_ by droplet infection
_ by droplet nuclei infection
_ by infected contaminated dust
particles
Examples of air borne infectious diseases:
Common cold,
influenza
sore throat
peneumonias
Pulmonary T.B
measles
mumpus
diphtheria
Chiken pox
whooping cough
scarlet fever
*methods of control: what to do
1. bed spacing
2. Dust control
3. Good ventilation
4. good health habit
5. Air disinfection
6. Use of masks
7. decrease over crowding
2. food and drink borne infection:
*methods of infection:
A.) INGESTION OF CONTAMINATED FOOD, WATER
AND MILK
B.) contaminated infected hands from excreta of patient or
carrier
C.) ingestion of infected meat
D.) house flies
E.)shell fish if taken from sewage
*example of diseases;
- dysentery amoebic
- shigellosis
cholera
- ascariasis
- typhoid fever
poisoning
- enteroviruses
- gastroenteritis
- enterobious vermicularis
- amoebiasis
-
- staphelococcal food
-hepatitis A
*methods of control : what to do ?
1. provision of safe and clean water which contain residual
amount of chlorine.
2. food sanitation
3. good washing vegetable with clean running water
4. control flies by using insecticides
5. sanitary sewage disposal
6. control restaurant and food handlers
7. personal hygiene(hand washing and health education)
8. provision of bublic health laboratory testing (milk, water,
food and meat
9. boiling or pasteurized of milk (143̊C
30 min) (163̊C
15 sec)
3. arthropod borne infection:
*methods of transmission of infection:
A.) by inoculation of insect bite.
B.)by contamination of skin wound or mucus membrane .
C.)by infective feaces of the vector.
D.) By infective body fluids of vector when crushed.
* types of vectors and examples of disease:
1. flies : enteric fever
gastroenteritis
typhoid fever
bacillary dysentery
2. louse : epidemic typhus
relapsing fever
3. fleas: plaque
endemic typhus
4. mosquitoes: malaria
filariasis
yellow fever
dengue fever
*methods of control:
1. use of fly swatter, insecticide, electric insect killer
2. screened window
3. clean lines
4. avoid over crowding
5. Avoid collection of dust in room
6. elimination of mosquito breeding places.
7. use of mosquito nets and fan for sleeping.
4. contact transmission infection:
*methods of transmission:
A.) By direct or indirect contact with infected lesion.
B.) by sexually transmitted
*examples of infectious disease:
1. bacteria :T.B. of skin
gonorrhea
2. viruses: herpes simplex viruses
papilloma viruses
AIDS
human
3. spirochates: syphilis
4. fungus: tinea capitis
scabies
Trachoma
Madura foot
tinea pedis
eye infectious disease
moniliasis
actinomycosis
*methods of control for sexually transmitted diseases:
1. Suitable medical treatment
2. avoid illegal sexual intercourse
3. strict personal cleanliness
4. prevent the use of infected material used by patient.
5. health
education.
3. protecting susceptible individual
*methods of protection:
1. by immunization
2. good vitamin-A for health skin and cornea
3. good nutrition increase resistance to infection
4. good health hygiene to avoid measles or other infectious disease.
5. avoid the exposure to allergen to prevent the start of allergic disease