Test: Epidemiology and Vaccines - 1 - NEET PG MCQ

• Is based on the single examination of a cross-section of a population ‘at one point of time’ , results of sample are then projected to whole population
• Is simplest form of observational epidemiological study
• Provides ‘Prevalence of the disease’ under study
• More useful for chronic diseases
• Tells about distribution of a disease in a population, ‘rather than its etiology’
• Gives ‘Snapshot of a population’
• Cannot establish causality as ‘does not establish time sequence’
• Provides little information about the natural history of disease or incidence

TOOLS OF MEASUREMENT IN EPIDEMIOLOGY:

• Rate: Numerator (a) is a part of denominator (b) and multiplier is 1000 or 10,000 or 100,000 or so on…
• Ratio: Numerator (a) is not a part of denominator (b) and BOTH numerator and denominator are unrelated
• Proportion: Numerator (a) is a part of denominator (b) and multiplier is 100
  • Proportion is always expressed in percentage (%)
• Incidence is a rate, Prevalence is a proportion

WHO RECOMMENDED DEATH CERTIFICATE (for International use):

• Consist of four lines:
  • Line Ia: Disease or condition directly leading to death
  • Line Ib: Antecedent/ underlying cause
  • Line Ic: MAIN ANTECEDENT/ UNDERLYING CAUSE
  • Line II: Other significant conditions contributing to death BUT not related to disease/ condition causing it
• Concept of underlying cause, Line Ic is the MOST IMPORTANT line in death certificate, thus also known as ‘Essence of Death Certificate’

• Adjusted or standardized rates:
  • While comparison of death rates of two populations, ‘crude death rate is not the right yardstick’, as age-compositions are different
  • Age-adjustment or age-standardization removes confounding effect of different age structures
• Indirect standardization: Standardized mortality ratio (SMR):
  • Is simplest and most useful form
  • Method: Calculate expected deaths, assuming that study group experiences the death rates of a standard population

Feasibility: Permits adjustment where age-specific rates (ASDRs) are not available or are unstable because of small numbers

Survival rate: Is the proportion of survivors in a group (e.g. of patients), studied and followed over a period of time (e.g. over a period of 5 years)

• Is used to ‘describe prognosis’ in certain disease conditions
• Can be used as a ‘yardstick for the assessment of standards of therapy’
• Survival period is usually reckoned from the date of diagnosis or start of the treatment
• Quite useful in cancer studies
• Survival rate calculation: 
  
• Specific death rate:
  • Help identify particular ‘at risk’ group(s) for preventive action
  • Permit comparison between different causes within same population

Specific death rate calculation:

Case fatality rate:

• CFR represents ‘killing power of a disease’
• It is ‘closely related to virulence of organism
• 

Proportional mortality rate: No. of deaths due to a particular cause (or in a specific age group) per 100 (or 1000) total deaths.

• Is ‘simplest measure of estimating the burden of a disease’ in the community
• Is a useful health status indicator: Indicates magnitude of preventable mortality

[According to older values of 2005, when question came in exam]
Almost 2/3rd of IMR occurs in neonatal period (IMR = 47 per 1000 LB and NNMR = 32 per 1000 LB)
Almost 2/3rd of the U5MR occurs in the first year of life (IMR = 47 per 1000 LB and U5MR = 63 per 1000 LB)
About one in ten children die before they reach the age of five years (U5MR = 63 per 1000 LB).

• Crude birth rate (CBR): Annual number of live births per 1000 mid-year population
• Crude death rate (CDR): Annual number of deaths per 1000 mid-year population
• Findings of SRS Bulletin: [2013]
  1. Crude Birth Rate (CBR): 21.6 per 1000 mid-year population
  2. Crude Death Rate (CDR): 7.0 per 1000 mid-year population

INDICATORS OF HEALTH:
Mortality indicators:

• Crude death rate (CDR)
• Life expectancy (LE)
• Infant mortality rate (IMR)
• Child mortality rate (CMR)
• Under 5 proportional mortality rate (U5MR)
• Maternal mortality rate (MMR)
• Disease specific mortality
• Proportional mortality rate

In the given question, in an outbreak of cholera in a village of 2000 population, 20 cases have occurred and 5 have died,
Thus, CFR = Total no. of deaths due to a disease/ Total no. of cases due to that disease × 100

And, Survival rate = 1 – CFR = 1 – 0.25 = 0.75 (75%)

Standard population: Is a population where numbers in each age and sex group are known

• Two frequently used standard populations are:
  1. Segi world population
  2. European standard population
• Choice of standard population is arbitrary:
  1. Available standard populations may be used
  2. Standard population may also be created using 2 populations
  3. The national population need not always be taken as the standard population
  4. Is commonly used in occupational studies: Comparison of mortality in an industry and general population
  5. Can be used for occurrence of disease (rather than death)