Epidemiological Measures of Morbidity and Mortality PDF

Epidemiological measures Indices of Morbidity and Mortality Dr Ali Khlaifat  ‫‪Dealing with numbers‬‬ ‫األرقام الهندية ‪ Indian numbers‬هي الرموز (‪٤ - ۳ - ۲ - ۱ - ۰‬‬ ‫‪)۹ - ۸ - ٧ - ٦ - ٥ -‬‬ ‫بينما االرقا...

Epidemiological measures Indices of Morbidity and Mortality Dr Ali Khlaifat  ‫‪Dealing with numbers‬‬ ‫األرقام الهندية ‪ Indian numbers‬هي الرموز (‪٤ - ۳ - ۲ - ۱ - ۰‬‬ ‫‪)۹ - ۸ - ٧ - ٦ - ٥ -‬‬ ‫بينما االرقام العربية ‪Arabic numbers‬‬ ‫‪1,2,3,4,5,6,7,8,9,10‬‬ ‫‪ Arabic numbers‬تُستعمل فيها فاصلتان‪ :‬النقطة لتفصل بين‬ ‫الصحيح والكسر‪ 5.25 :‬والفاصلة العاديّة لتفصل ك ّل ثالث منازل‬ ‫على حدة‪. 1000,000,000 :‬‬ ‫في االرقام الهندية ال يوجد فواصل لفصل منازل االعداد والفواصل التي‬ ‫تستعمل في ‪ Arabic numbers‬مثل )‪(dot -.- which = ziro‬‬ ‫أو ) ‪(coma - ,- = used for decimal numbers‬‬ Epidemiological measures / outcome of epidemiological studies and reports Measures of disease frequency (quantity)  Counts  Proportion (percentage)  Rate  Ratio  Epidemiological measures 1. Counts Simplest & most basic measure - absolute number of persons who have disease or characteristic of interest For examples:  AIDS in Jordan is 500 cases  To date we have 153 COVID-19 cases in including 50 cases aged less than 30 years.  Useful for health planners & administrators: for allocation of resources  used for surveillance of infectious disease for early detection of outbreaks Counts don’t tell us about - the size of the population at risk - The duration of observation 4  Epidemiological measures 2- Proportion : A proportion is a ratio in which the numerator is a subset (or part) of the denominator and can be written as a/(a+b) − A relative frequency. Example: From 8000 females aged 16 – 45 y in the town 2,400 use modern contraceptive methods. The proportion of those who use modern contraceptive methods = 2,400 / 7,999 x 100 = 30%. So, it is users divided by users and non-users.  Epidemiological measures 3- Rate Measure of frequency of an event for a defined population during a specified period of time. RATE = Components of a Rate: Numerator Specified time period Denominator K : Constant multiplier  Epidemiological measures Rate is similar to proportion but specified by the time – the events Numerator-‫البسط‬-Number of events in a population. The top number in a rate Denominator- ‫المقام‬- The total population at risk. The bottom number in a rate Need to match these when calculating a rate ( ‫ اشارة الى زمن‬،‫ نفس المجتمع‬،‫البسط له نفس خصائص المقام‬ )‫موحد‬ A rate may or may not be a proportion 7  Calculating Rates- Example Death Rate for Maan City in 2018 Numerator = the number of deaths in Maan City in 2018 = 300 Denominator = the total population of Maan City in 2018 = 60,000 Time Period = 2018 Constant = 100,0 Death rate in Maan City in 2018 = 8  Calculating Rates- Example The previous results can be read like that: the death rate in Maan City in 2018 was deaths per thousand people ‫يساوي خمسة‬ 2018 ‫نسبة الوفيات في مدينة معان في عام‬. ‫وفيات لكل الف مواطن‬ Note: the constant number is important to consider but the most important is to know how to change from constant to other: e.g. 5/1000 is the same as 50/10,000 or 500/100,000 9  Ratio 3. Ratio: when the values of x and y may be independent, the relationship expressed as : Also defined as A fraction in which the numerator is not part of the denominator. Example Read some times as F:M While Proportion : when X is part of Y. Female. Male+female  Ratio Note that F:M is different to M:F where when it expressed in numbers will need to change the position of the numbers. e.g. if we have 20 female and 10 male the equation will be as follow: F:M = Read as : female male ratio is 2 to 1 But male to female ratio will be M:F = Read as M:F ratio is 1 to 2  Calculating Rates-notes Rates in epidemiology usually is a measure of risk in a defined population (in the rate equation represents the DENOMINATOR For any measure of disease frequency, precise definition of the denominator is essential for accuracy and clarity. Note: when individuals not at risk of the disease are included in the denominator (population at risk) the resultant measure of disease frequency will underestimate the true incidence of disease in the population under investigation. This usually applicable on diseases with high of immunity (natural), or acquired: Vaccine-preventable infections.. E.g. measles However, this is not always possible in practice in population estimates for diseases represents small portion.. E.g. diabetes Population at risk  Calculating Rates-notes Usually in denominator used the “mid-year population”.. The mid-year population estimates relate to the usually resident population on 30 June of each year. The mid-year population appears to be the most suitable standard for comparability with regard to time reference; and it is in most cases a practically sufficient approximation for the computation of annual rates, such as birth, death and marriage rates, annual per capita income, production and consumption.  Common Measures in Epidemiology: Morbidity Measures: – Incidence Rate o Natality Measures: – Prevelance Rate Crude Birth Rate – Attack rate Mortality Measures: Fertility Rate – Case fatality rate o Risk measures: – Crude Mortality Rate Relative Risk (RR) – Infant Mortality Rate – Maternal Mortality Rate Odds Ration – Under-five Mortality Rate – Age-specific Mortality Rate – Cause-specifice Mortality Rate  Morbidity measures Morbidity Measures: Measures of disease frequency are used to describe how common an illness (or other health event) is with reference to the size of the population (the population at risk) and a measure of time. There are three main measures of disease frequency: – Incidence Rate – Prevelance Rate – Attach rate  Incidence Rate A measure of all new cases of a disease in a population over a period of time (mostly one year). * 100,000  Incidence rate  An incidence rate describes how quickly disease occurs in a population  Trend of diseases is best understood by incidence rate and epidemics are identified.  provides the capacity to anticipate future incidents and plan accordingly  It give how much the individual have risk to develop or get the disease  The incidence rate can be further categorized by different characteristics such as race, gender, or age.  Useful for etiology studies – cohort studies  Disease spread- Diseases spread usually classified based on surveillance results in relation to the time being covered (known as Level of disease): Sporadic refers to a disease that occurs infrequently and irregularly. Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Endemic refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area 19  Disease spread- cont. Hyperendemic refers to persistent, high levels of disease occurrence. Outbreak carries the same definition of epidemic, but is often used for a more limited geographic area. Cluster refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known. Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people. 20  Epidemics occur when an agent and susceptible hosts are present in adequate numbers, and the agent can be effectively conveyed from a source to the susceptible hosts. More specifically, an epidemic may result from: A recent increase in amount or virulence of the agent, The recent introduction of the agent into a setting where it has not been before, An enhanced mode of transmission so that more susceptible persons are exposed, A change in the susceptibility of the host response to the agent, and/or Factors that increase host exposure or involve introduction through new portals of entry. 21  Incidence rate-example For example, 200 new cases (numerator) of acquired immunodeficiency syndrome (AIDS) were reported in the Jordan in 2018. For 2018, the Jordan mid-year estimated population was 1000,000,0 (denominator). Therefore, the incidence rate for AIDS in the Jordan. so in 2018 Incidence rate of AIDS was = (200 ⁄ 1000.000,0) = 0.00002 of AIDS per person. Here we will express the rate per 100,000 of the population 0.00002 x 100000 = 2 /100000= 2 new cases per 100,000 population  The most accurate way of calculating incidence is to calculate the “person-time incidence rate.” Each person in the study population (usually cohort studies) contributes one person-year to the denominator for each year (or day, week, month) of observation before disease develops,  Measures of disease occurence (morbidity) Prevalence Rate (burden) Measures number of people in a population who have the disease at a given time. Includes new cases and previously contracted cases. Number of existing cases of a disease (at a specified time period) * K Total Population at mid-point of time period 24  The relationship between prevalence and incidence Incidence: risk Prevalence: burden prevalence and incidence are closely related. - Prevalence depends on: 1. The incidence rate (risk) 2. The duration of disease (time)  The relationship between prevalence and incidence For example: chronic, incurable disease, such as diabetes, can have a low incidence but high prevalence, because the disease is not very fatal—but it cannot be completely cured either − Its prevalence is the sum of new and existing cases from past years A short-duration, curable disease, such as the common cold, can have a high incidence but low prevalence, because many people get a cold each year—but it lasts for a short time The relationship between prevalence and incidence if the incidence of a disease is high and the duration of the disease is short, the prevalence will be low relative to the incidence. For example, acute conditions like most infectious diseases that have a relatively short duration (a few days). either due to quick recovery (e.g. diarrhea, influenza) or due to high fatality (plaque or cholera in poor areas).  Attack rate (AR) The attack rate is similar to the incidence rate used when describing diseases occurred in short times and limited areas such as outbreaks : in reporting outbreaks of food poisoning or salmonella infections in group of people, small villages or neighborhoods..etc Ex: Outbreak of cholera in country X in March 1999 – Number of cases = 490 – Population at risk = 18,600 – Attack rate =490/18600 * 100 = 2.6%  Crude Death Rate The crude death rate is a measure of the actual observed mortality in a given population. Crude death rate (CDR) = Total number of deaths in specified time X 1,000 Total population in the same time example: In 2019, number of deaths for Jordan was 38.78 thousand cases deaths occurred. The estimated population was 10,101,694. The crude mortality rate in 2019 was, therefore, (38780 ⁄ 10,101,694) × 100,000, = 383.9 deaths per 100,000 population  Crude death rate (CDR) The main disadvantage of the crude mortality rate is that it does not take into account the fact that the chance of dying varies according to age, sex, race, socioeconomic class and other factors. Comparisons of mortality rates between groups of diverse age structure are usually based on age standardized rates.  Adjusted rate or standardized rate Standardization may be used to adjust for the effects of a variety of confounding factors including age, sex, race or socio-economic status. Standardized rates are used for the comparison of two or more populations; they represent a weighted average of the age specific rates taken from a 'standard population' and are not actual rates. Adjusted rate or standardized rate usually calculated to make possible the comparability between populations with different demographic structure (age structure for example) 1- Crude rates 147/14000000 *1000=10.5/1000 15300/2170000*1000= 7/1000  2- Adjusted or standardized rate Standard population  Proportionate Mortality Ratio = PMR of cancer in Jordan : number of cancer death = 5000 Total number of deaths = 38000 PMR of cancer = 5000/38000 * 100 = 13.2 % It is used for Ranking of Deaths for Leading Causes of Death. When we know the PMR for all causes the sum will be 100%  Cause-specific mortality rate The cause-specific mortality rate is the mortality rate from a specified cause for a population. It is a portion of crude death rate Cause-specific mortality rate = Number of deaths from a specific cause X 100,000 Total population In 2007 a total of 992 deaths caused by Road Traffic accidents (RTA), how much RTA specific mortality rate in Jordan in 2007, population was 5728000 There was 17.32 death caused by RTA per 100,000 population Dr.Ali Khlaifat 38  Case-fatality (CFR) CFR is The case-fatality rate is the proportion of persons with a particular condition (cases) who die from that condition. It is a measure of the severity of the condition. The formula is: Example: In an epidemic of hepatitis A traced to green onions from a restaurant, 555 cases were identified. Three of the case- patients died as a result of their infections. Calculate the case- fatality rate. Case fatality rate = (3 ⁄ 555) × 100 = 0.5%  Age-specific mortality rate An age-specific mortality rate is a mortality rate limited to a particular age group. The numerator is the number of deaths in that age group; the denominator is the number of persons in that age group in the population Ex. In the United States in 2003, a total of 130,761 deaths occurred among persons aged 25–44 years (85464705) equals (153.0 deaths per 100,000 25–44 year olds. ) Some specific types of age-specific mortality rates are neonatal, and infant mortality rates, will be described in the following sections.  Maternal mortality rate The maternal mortality rate is really a ratio used to measure mortality associated with pregnancy. The numerator is the number of deaths during a given time period among women while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and the site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes. The denominator is the number of live births reported during the same time period. Maternal mortality rate is usually expressed per 100,000 live births. Number of maternal deaths X 100,000 Total number of live births  Maternal mortality rate In 2007, 76 maternal deaths were identified out of 397 588 live births in Jordan, for a maternal mortality ratio of 19.1 deaths per 100 000 live births. Live births Amarin Z et al. National maternal mortality ratio for Jordan, 2007–2008. International Journal of Gynaecology and Obstetrics, 2010, 111:152–156.  Infant mortality rate (IMR) The infant mortality rate is commonly used as an indicator of the level of health in a community. It measures the rate of death in children during the first year of life, the denominator being the number of live births in the same year. The infant mortality rate is calculated as follows: Number of infant deaths X 1,000 Total number of live births The use of infant mortality rates as a measure of overall health status for a given population is based on the assumption that it is particularly sensitive to socioeconomic changes and to health care interventions. Dr.Ali Khlaifat 43  Under-5 mortality rate (U5MR) also known as child mortality rate: The child mortality rate, or the 'under-five mortality rate', refers to the probability of dying between birth and exactly five years of age (aged 5 are not included) expressed per 1,000 live births. frequently used as a basic health indicator. Injuries, malnutrition, congenital malformation and infectious diseases are common causes of death in this age group. Trend of Infant & under 5 mortality 1990-2015  Example: in 2019 there was 2740 death in age 0-1 year and 3000 deaths in age < 5 years and 200000 live births IMR = U5MR =  Neonatal mortality rate Neonatal mortality refers to death of a live- born baby within the first 28 days of life Number of neonatal deaths X 1,000 Total number of live births Suppose we have 2000 death before 28 days age and the same year we have 200000 live births.. Calculate NMR … 2000/200000*1000 = 10/ 1000 =10 deaths of babies asged 28 days or less per 1000 live birth  Natality (Birth) Measures Natality measures are population-based measures of birth. Crude birth rate = Crude fertility rate :  Measures of risk Risk refers to the likelihood that people who are without a disease, but who come in contact with certain factors thought to increase disease risk, will acquire the disease. There are two measures of risk commonly used in epidemiological studies: - relative risk: derived from cohort studies - odds ratio: derived from case-control studies  Relative risk is a term for the risk in an exposed group relative to that for the comparison group. it is a ratio of two rates: Incidence rate among exposed and Incidence rate among nonexposed relative risk (RR) = Incidence rate among exposed Incidence rate among nonexposed