Principles Of Epidemiology Flashcards
What is the purpose of epidemiology
To obtain, interpret and use health information to promote health and reduce diseases
What’s re the four phases in the use of epidemiological approach
Descriptive epidemiology
•Analytical epidemiology
•Intervention or experimental epidemiology
•Evaluation epidemiology
Which use of epidemiological approach is concerned with the Concerned with disease distribution and frequency •Ask –What •Problem •Frequency –Who –Where –When
Descriptive
Which use of epidemiological approach is concerned with Analysing the causes, or determinants of diseases by testing hypothesis
•Answer questions such as
–How is the disease caused?
–Why is it continuing ?
Analytical epidemiology
What is intervention or experimental epidemiology
Clinical and community trials to check for
–Intervention or programme effectiveness
–For improving underlying conditions
What is evaluation epidemiology
Measures the effectiveness of different health services and programmes
•Answer question
–So what?
–Have there been any improvement in health status?
Epidemiology aims about Information needed for:
– Planning
–Managing
–Evaluating
•All the activities required to promote health and to prevent and control disease
True or false
True
What is the denominator population
Population at risk (denominator population)
–People at risk of developing a disease or having a health problem
–People currently suffering from it
The concept of denominator help develop the information needed for:
–Health planning
–Management of health programmes
–Evaluation of health promotion and disease control activities true or false
True
Example of who variables,where variables and when examples in descriptive epidemiology
Age –Sex –Education –Occupation –Income –Cultural and religious group –Family size –Nutritional state –Immune status
•Other characteristics –Hospital attendance –Birth weight –Sanitation in households Where? •Variables –Town, village or isolated dwelling –High or low altitude –Proximity to river, forest, wild animals or sources of toxic substances –Distance from health services
When?
New cases of Avian Infuenza per day
•New cases of malaria per week
•New pregnant mothers registering per month
•New cases of HIV in one year
Wht Is the best indicator for assessing the condition of event/case/episode
Incidence
What It is the best measure for evaluating health programme effectiveness
–Used in disease surveillance and for analyzing the use of health services
Incidence
What is used to measure frequency
Incidence and prevalence
Incidence is used for Useful for diseases with short average duration
True or false
True
Prevalence is Total number of existing cases/episodes/events occurring at one point in time commonly on a particular day
–Prevalence = Incidence x average duration of the condition
–Useful for chronic conditions
True or false
True
What kind of surveillance provides prevalence information
Cross sectional survey
Numbers are the most readily available data
•Often used in monitoring the occurrence of important infectious disease, esp.
–in outbreaks
–When
•populations are restricted in time and locality and
•population structure is assumed to be stable
True or false
True
•Rates are calculated by relating the cases to the population that which has given rise to them.
•Number of cases (numerator)
–Made up by counting people, episodes or attendances.
•Total population at risk (denominator)
•Rates must have time period or a date attached to it which must always be stated
True or false
True
Stage two uses of rates
To make comparisons
•To calculate the number of expected cases
What are the formulas for incidence and prevalence rates
Incidence rate= new cases in specified period of time x factor
total population at risk
•Prevalence rate= existing cases at specified point of time x factor
total population at risk
In estimating the prevalence rate of a particular disease, the denominator used should be;
– the total number of individuals who may be at risk of contracting the disease in question true or false
True
In case of survey, denominator may comprise of all individuals in the sample.
•For age-sex specific rates, the denominator includes only the people in relevant age-sex groups.
True or false
True
In estimating effectiveness of a programme we need total number of new episodes (incidence) commonly in one year
•In studying use of health services, we look at information on new and repeated attendance
True or false
True
How are cases classified
Possible
•Cases which have symptoms of possible disease (fever, headache, body aches)
–Probable
•Possible cases who also respond to treatment
–Definite
•Probable cases who test positive to diagnostic test
What are health indicators and importance of health indicators
Indicators are measures used to describe an existing situation and to measure changes or trends over a period of time
To analyse present situation
•Make comparisons
•Measure changes over time
•Provide measures for development
Health indicators may measure the actual situation directly
–IMR direct measure of actual risk of infants dying in their first year of life
–Indirectly as a measure of overall socioeconomic development
True or false
True
Name five sources of information for calculating health indicators
Registration of births, death ad diseases •Population censuses •Routine health information systems •Surveillance •Investigation of epidemics •Sample surveys
What’s re the types of health indicators
Health policy
–Level of political commitment to PHC
–Availability of public policy statements and health plans
–Degree of equity in the distribution of resources
•Social and economic development
–Level and distribution of economic wealth
–Types and levels of employment
–School enrolment and adult literacy
–Household food security
•Population
–Age-sex structure
–Density, distribution and migration
–Population growth: birth and death rate, fertility and rate of natural increase
•Provision of health care
–Access to health care and facilities and coverage by the 8 essential elements of PHC
–Resource availability
•Health status
–Nutritional, morbidity and mortality
Health policy indicators Social and economic development indicators Population indicators Provision of health care indicators Health status indicators
Morbidity indicators are based on? And name three mortality indicators (morbidity and mortality indicators are health status indicators)
Based on disease specific incidence or prevalence rate for common and severe diseases •Mortality indicators –Crude mortality rate –Infant mortality rate –Under five mortality
Infant under 1year make up 3-4% of total population
–Children under five (about 18-20%)
–Children 0-14 years (about 40-44%)
–Women in fertile age range (15-44 years) 20-22%
–Women and young children 40%
What kind of country does this population census represent and what is the importance of population census
Developing county and it These rates help estimate absolute number per population group
Age-sex structure can be show by population pyramid using the percentage of males and females in each 5 year age group
•Population pyramids provides an estimate of denominators (at risk population) for calculating
–Age and sex specific rates
True or false
True
What is population density and its importance
The average number of persons per square kilometre (km2)
•Density may vary from place to place
•Useful for planning health services and in evaluating the access to and coverage of different health programmes
Crude birth rate is estimated from?
Estimated from census or
–special demographic survey
What is the formula for crude birth rate and total birth and what is the crude birth rate for high fertility countries and low fertility countries
CBR= Total births in one year/total midyear population (all ages, same year) x 1000
–High fertility countries – 45births per 1000 per year
–Low fertility countries- 20births per 1000per year
–Could be use in estimating the total number of births per year
•Total birth = CBR/1000x population per year
Fertility rate (FR) is an age-sex specific rate usually derived from census or special demographic survey •It’s a measure of how frequent women in the fertile age range are having babies What is the fertility rate of women in developing countries
Developing countries have between 100-150 births per 1000 women aged 15-44 years
What is the formula for crude death rate, infant mortality rate and child mortality rate and maternal mortality rate and what is the infant mortality rate in developing countries
Crude death rate
– total death in one year/total midyear population (all ages, same year)x 1000
•Infant mortality rate
– the proportion of all liveborn infants who die in the first twelve months of life
– total infant (aged < 1 year) deaths during one year/total births in the same year x1000
–
In developing countries rates range between 60-150 infant deaths per 1000 births per year in severe conditions 200
•Neonatal mortality is infant deaths in the first 1month of life
Demographic rates
•Child mortality rate: based on deaths between 1-4 years
Maternal mortality rate
–Maternal pregnancy related deaths in one year/ total births in same year x factor (1000 or 100000)
What is population growth and the formula for rate of natural increase or RNI
Population growth
–Balance between the number be of births and people migrating into the an area on one hand and the number of deaths and people migrating out the area on another hand
•Rate of natural increase
- RNI=CBR-CDR
Name two sources of population information
Census report
•Studies report
Accuracy of population data is limited by
Resources available for their collection
–The level of socioeconomic development
–Educational and cultural sophistication of the population itself
Age is one of the most difficult variable to ascertain accuracy.
•It is closely related to disease patterns
•People may not know their age but may know the year they were born
•Asking both questions can help validate age
•Age can also be estimated according to a calendar of notable events
–Eg how many years after independence were you born as a way of improving accuracy of population characteristics
True or false
True
Sex is important to record because of the physiological and behaviour patterns in the two sexes
•The sex composition of a survey population and a general population can invalidate result
•The under enumeration of women is high in most surveys
True or false
True
Ethnic group share similar social and cultural characteristics which does influence disease patterns
–thus, differences in disease frequencies among ethnic groups
True or false
True
Marital status
•A precise definition of married and separated may be problematic in some societies
•These are mainly due to the social roles attached to the status.
True or false
True
Occupation
•There is the need to decide whether the past or present occupation is needed.
•This would be important in identifying risk respondent could be exposed to.
True or false
True
Name five demographic variables
Marital status Occupation Ethnic group Sex Age Religion Place of residence
The most available source of morbidity data is hospital records
True or false
True
What are the two ways important diseases may be under recognized by district information system
If disease has low frequency (incidence or prevalence)
–When illness does not produce clear symptoms and signs that are easily recognized by the people or health workers eg malnutrition
•These require special surveys and research studies for subclinical and chronic infections
•Same applies to mental disability and eye diseases
Reliable disease specific incidence or prevalence rates could be used to calculate approximate number of cases
Therefore what is the formula for number of cases
No of Cases = prevalence rate x total population
–Useful for chronic diseases
–Could be affected by seasonal or annual fluctuation
–Useful in assessing the effectiveness of health services
–Exposes the limitations in relying on incidence and prevalence rates calculated from cases reported by routine information systems
A small increase in the total number of cases or deaths may signify that an undetected epidemic is already under way in the community
What is the formula for case fatality rate
Case fatality rate= number of patients dying from a disease/number of cases of the disease, diagnosed in same period x 100
–Useful in assessing the quality of treatment given by medical services
–Case fatality of 15% is high
–Must be interpreted taking into accounts the severity of illness
–Case fatality in epidemics can give clear indication of the severity of illness and could help identify disease causing the epidemic
Death certification records the cause of a person’s death, as stated by a doctor or another responsible health worker.
death registration can be useful in compiling mortality statistics and in the surveillance of specific diseases.
•Could be useful in evaluating disease control activities and a rise in certified deaths from
–a particular cause may indicate a serious outbreak
–Mortality data has the advantage of been more accurate than morbidity data
–Disadvantage is that only fatal cases are included
–Data might be deficient when not certified by a doctor
–Under- registration of deaths
Medical Certification compiling statistics, deaths are classified by underlying causes and not the direct cause.
True or false
True
The collection and reporting of health information data is country specific
What is its purpose
The purpose of data collection is to support:
– Management and evaluation of health activities
How do health information systems work
Health facilities,communities detect new cases,collect the info about it,analyze the info and send the info to the regional level and it send a it to the ministry of health where info is reported and disseminated
Then they also improve health planning and implement necessary changes in those health facilities and communities
For a system to be useful, it does not have to detect all cases
•Good estimates of incidence can be invaluable for planning and evaluation of health programmes
True or false
True
Trends over time can be forecast when proportion of cases detected remains constant over time
•Incomplete data are better than none, provided the problems and defects in the data are
True or false
True
What’s re the two ways surveillance is used
The continuous scrutiny of the factors that determine the occurrence and distribution of disease and other conditions of ill health.
i. It is essential for effective control and prevention
ii. Includes the collection, analysis, interpretation and distribution of relevant data
iii. Similar to health information system
2. A special system which is set up for particularly important health or disease eg
i. Spread of communicable disease in a disaster
ii. Nutritional status in a famine or an epidemic
What is the aim of surveillance
To provide quickly information which can be analysed to determine frequency (Usually incidence), and to answer questions: who? Where? And when?
Name five uses of epidemiological surveillance
To identify outbreaks and epidemics to ensure effective actions
•To monitor the implementation and effectiveness of control programmes
•To assist in the planning of health programmes
•To identify high risk groups, geographical areas and variations over time
•To increase knowledge on causative agents and dynamics of transmission of communicable disease
Name three diseases under international health regulation, five diseases under global surveillance and four diseases under research
International health regulation (Download and read)
–3 diseases namely cholera, plague and yellow fever)
•Global surveillance
–5 diseases (typhus, influenza, malaria, poliomyelities and relapse fever) currently we have NCDs and childhood obesity
•UNDP/WB/WHO Special programmes for research
–Filariasis, leishmaniasis, leprosy, malaria,
What is the possible diagnosis for these symptoms Fever with red rash, red eyes, disappearing within a week
Malaria
What is the symptom of poliomyelitis
Fever with paralysis
Symptoms of cholera are
Sudden and severe watery diarrhoea with massive and rapid dehydration
Symptoms of African trypanosomiasis
Fever, swollen glands in back of neck, lassitude, headache, sleepiness
What is the possible diagnosis for this disease Segments expelled in faeces
Tapeworm disease
Fever, rigors, headache, body aches, inability to carry out normal daily activities
What causes these symptoms
Malaria
Name five sources of information in health information systems
Health facilities
–Main source of information
–Information sent in forms of reports
Death registration
–Useful in areas where a high proportion of deaths are registered
–Can be useful in epidemics when a few deaths are dispersed over a wide area
•
Laboratories
–Useful for information based on special test that isolate an infectious organism or confirm diagnosis
–Challenge in the distribution of laboratories
Community surveillance of limited number of key diseases and problems
–Useful to staff employed in special programmes such as malaria and family planning
–Uses simple standardized diagnostic criteria
Special searches
–Schools, markets, particular villages, and high risk households for case dections
•
Investigation of outbreaks
–Outbreaks require active case finding by surveys and details recorded and notified
•
Surveys
–Useful for periodic surveillance of some conditions
–Useful in estimating coverage of regular reporting or surveillance systems and
What’s re the deficiencies of health facilities as a source of information
Use of health facilities is influenced by
•Distant from homes
•Cost of treatment
•Uneven distribution of facilities among communities
•Local attitude to disease or conditions
Reporting on cases are done by analysing registered data on basis of
–Who (age and sex)
–Where (village of onset
•Ideally cases should be reported by date of onset but it is practically impossible so date of diagnosis is usually reported
•Trend analysis could also be performed
True or false
True
Information from a reporting or surveillance systems must be communicated with relevant stakeholders
–Ministry of health
–Primary health care workers and district staff
–Village councils and organisations
–Nongovernmental and voluntary organisations
–Local mass media, radio
•The usefulness in improving planning of health programmes and disease control activities.
True or fake
True
Most important epidemics are due to communicable diseases with short incubation period that are easily transmitted.
–E.g. food borne diseases and cholera
•The epidemicity is relative to the previous incidence of the disease in the same area, among specific population groups and at different seasons of the year.
True or false
True
Name three causes of epidemics
Food borne outbreaks
–E.g. enteritis due to Escherichia coli, staphylococcal infection, salmonellosis
•Communicable disease with short incubation period
–E.g. Dengue, cholera, influenza, malaria, measles, plague, yellow fever
•Toxic substances
–E.g. contaminated foods, insecticides and agricultural chemicals
How to detect epidemics
Community leaders, such as Assembly men and teachers
•Health workers in primary health care facilities
•District health information and surveillance system
•Hospitals
•Epidemics could highly be a political issues and reporting must be done with absolute caution
How to describe epidemics
Information on age, sex, residence and occupation of known cases in needed
•Date and time of onset and the whereabout of cases during incubation of disease
•Basic questions to consider
–What is the disease causing the outbreak?
–What is the source?
–What is the mode of transmission?
–How an the epidemic be explained?
•Who, when and where analysis required
What is epidemic incidence curb
Epidemic incidence curve •Is a graph that plot cases of the disease by time of onset of the illness. •The graph can indicate – the nature of the outbreak –Probable source
Difference between point source and extended point source
Point source or common source
–Where there has been simultaneous exposure of many susceptible to a pathogenic agent resulting in a rise in the incidence of cases of the disease over a short time.
–Characteristics of water borne and food borne diseases
•
Extended point source
–where the point source provides continuous exposure over a longer period of time
Common to shigellosis
The shape of a propagated epidecim curve depends on
incubation period of the disease and
–Suitability of the environment for transmission
The longer the incubation period, the more spread out the cases will be.
•Contact spread outbreak,
–the crowding and intimacy of contact will determine the rapidity epidemic reaches a peak
–While the proportion of susceptible population will influence the extent of the outbreak
True or false
True
Analysis of cases by who personal factors such as age, sex and occupation may also give clue to source of the infection
•It may be important to calculate attack rate in different population groups
The clustering of cases together in one area about the same time indicates a localized epidemic true or false
True
How is case control analysis done
Descriptive analysis by who, where? And when?
–may provide sufficient information about the source of the outbreak for immediate appropriate control action
•Case control study is often used
–Patients are questioned to assess their possible contact with the source as suggested by the incubation period
–Similarly controls from the same area who do not have the disease are posed the same questions
Importance of attack rates
Useful in food borne epidemic
•Comparing the attack rate for illness among the exposed to the unexposed
–(those who ate a particular food to those who did not)
Elements in the control of epidemics
Attack source and mode of transmission
•Treat and isolate all cases
•Increase resistance of local population
•Continue surveillance
What are the main strategies for control of. A communicable disease epidemic
Attack the source: Treat the case and carriers Isolate cases Surveillance of suspects Control of animal reservoirs Notification of cases
Interrupt transmission : Environmental hygiene Personal hygiene Vector control Disinfection and sterilization Restrict population movements
Protect susceptible people: Immunization Chemoprophylaxis Personal protection Better nutrition
a relative risk of 1.5 means that the risk of the outcome of interest is 50% higher in the exposed group than in the unexposed group, while a relative risk of 3.0 means that the risk in the exposed group is three times as high as in the unexposed group
True or false
True
For example, if the absolute risk of a condition is 30% in the reference population, then an RR of 1.2 means that this risk will increase by 20% after exposure to the risk factor. As 20% of 30 is 6%, the absolute risk will rise from 30% to 36% in patients exposed to the risk factor.
True or false
True
