Spectrum of Disease and The Iceberg Phenomenon

Epidemics are sudden and widespread disease outbreaks in a particular community or region. Understanding the types of epidemics, such as common-source, propagated, and mixed epidemics is important for their control and management. 

NEET PG may test your knowledge of the different epidemics and their management strategies. The topics of "Types of Epidemics," "Levels of Prevention of Disease," and "Iceberg Phenomenon of Disease" are particularly important for the NEET PG exam.

Read this blog further for a quick overview of this important PSM topic for NEET PG exam preparations.

Index

Combination of indicators

HDI

Literacy Rate is known by different synonymous 

• Education index 
• Enrolment ratio in schools
• Knowledge 
• Mean years of School

Income measured in

• Per capita (or) US $ PPP (Purchasing power parity)

Life expectancy is also known as longevity at birth or LE₀ in HDI or  LE₁ in PQLI

Important Information

• PQLI: 0 - 100; PQLI of India: 65 
• HDI: 0 - +1, HDI of India: 0.640, Rank: 129
• Norway: HDI of 0.95 is the most developed country

MDPI (Multidimensional Poverty Index) has 3 Indicators further comprised of 10 sub-indicators

• Health
• Education
• Living Standard  

MDPI will define the person as poor, if there is deprivation in >33% of the indicators. It has 3 main Indicators which lie between 0 to +1. Based on MDPI India has a 27.9% poor population.

Below Poverty Line (BPL) Criteria

• Based on Income per Capita, currently 29.5% of the Indian population is living below the poverty line.

Also Read: Clinical Trials: Animal and Human Study

Time Distribution of Disease

• Short-term fluctuations: Epidemics 
  • E.g.: Food poisoning, Bhopal Gas tragedy 
• Long-term fluctuation: Secular Trend
  • E.g.: Non-communicable disease (DH, CAD)
• Periodic fluctuations
  • Seasonal Trend: Disease that increases every particular season 
  • E.g.: Malaria, Dengue in the rainy season, RTI in winter season
  • Cyclical Trend: Fluctuations in every few years
  • E.g.
    • Measles, Rubella, Influenza 
    • Measles every 2-3 years 
    • Rubella every 5-8 years 

Important Information

• Influenza shows maximum change in trend due to antigenic shift/drift

Types of Epidemics

1. Single Exposure Point Source Epidemic (SEPSE)

• Sudden Rise and Sudden Fall in no. of cases 
• Cluster of cases in a single incubation period.
• E.g.: Staph food poisoning/Bhopal gas tragedy

2. Multiple Exposure Point Source Epidemic (MEPSE)

• Sudden rise in no. of cases, but fall in no. of cases is not sudden but interrupted by multiple peaks.
• These multiple peaks are known as secondary waves
• E.g.
  • Contaminated Water Supply/Well in Village
  • HIV through Commercial Sex Worker    

3. Propagated Epidemic

• Person to-person transmission 
• Slow rise in population → Plateau → Slow fall 
• Absence of peak
• E.g.: HIV, TB, Hep-A, Recurrence of Polio

Control of Disease 

• Control: Reduction in transmission so that it stops to be a public health problem.
• It has 4 components
  • Reduction of incidence
  • Reduction of duration 
  • Reduction of complications 
  • Reduction of the financial burden of disease
• Elimination: Complete interruption of transmission, but the organism is still present, so the disease can make a comeback. (Country/ Region) 
• Eradication: Complete extermination of the organism (World)
• India has been declared free status of 2 diseases namely
  • Trachoma 
  • Polio 
• Only Smallpox has been eradicated from the world on 8 May 1980
• Only 2 strains of poliovirus have been eradicated and not the disease
  • P₂: 20th September 2015 
  • P₃: October 2019

Levels of Prevention of Disease

1. Primordial: Before the emergence of risk factors 
   • Examples of Primordial: Source reduction in Malaria (i.e. stranded water)
2. Primary: Risk factors present but no disease yet 
   • Health promotion & specific protection
   • Primary can prevent
     • Examples of 1°: Vaccine and contraceptives; Mosquito Nets and Gambusia fish, masks, social distancing
3. Secondary: Disease has possibly started
   • Early diagnosis and treatment
   • Cannot prevent
     • Examples of 2°: PBS of Malaria, Sputum smears examination for TB, drug Remdesivir, Western blot for HIV, PAP smear, ATT, MDT (multi-drug therapy), ACT
4. Tertiary: Disease is in progression
   • Disability limitation and rehabilitation
   • Spectacles are also visual rehabilitation
     • Examples of 3°: Crutches in Polio, Spectacles

ICD-II (INTERNATIONAL CLASSIFICATION OF DISEASES)

• It contains 3 Volumes and has 26 chapters along with chapter X, V.
• I Volume: Tabulation list
• II Volume: Reference guide
• III Volume: Alphabetical Index                
• Chapter X: Extension quotes
• Chapter V: Functional assessment
• Revised every 10 years, right now 11^th edition released in June 2018
• Chapter 6: Mental behavioral and Neurodevelopmental disorders
• Chapter 26: Traditional medicine
• Chapter 21: Disease of unknown etiology

PSM Related Articles:

Spectrum of Disease

• It is a graphical representation of variation in the manifestation of diseases.
• When a person suffers from a disease, It could become either a clinical case or the person could recover, or in an inverse case scenario, the person could even die. Those are called the spectrum of disease.
  • Subclinical infection,
  • Clinical infection,
  • Mild illness,
  • Severe illness,
  • Fatal illness
  • Death.
• The disease that does not follow the spectrum of disease principle is rabies. Leprosy is a disease that perfectly follows the spectrum of disease principles.

Cases

• Primary Case: First case of the disease in a community 
• Secondary Case: All cases that occur after 1° case 
• Index Case: First case which comes to the notice of the Investigator
  • It can be either a primary or secondary case but usually it is a secondary case in a developing country like India.

Carriers 

• Contact C: A person who comes in contact with a case and himself becomes a carrier
• Paradoxical C: A person gets infected by another carrier and himself becomes a carrier.
• Chronic C: Carrier State > 6 months 
• Incubatory C: Person shedding organism even in the Incubation period of the disease, is yet to develop symptoms, but infecting others
• Convalescent C: Person shedding organism even in convalescence (Recovery phase)
• Important Information
  • Pseudo C: Carrier of a virulent organism, no manifestations produced
• Incubation period: Entry of organism in the human body till the first sign/symptom is produced
• Serial Interval: Interval between primary case and secondary case
• Generation time: Time between entry of organism in the human body till maximum infectivity of a person

ICEBERG PHENOMENON OF DISEASE

The "iceberg phenomenon of disease" theory explains how an illness progresses from its preclinical stages to its overt or apparent state. The submerged portion of the iceberg represents the hidden mass of the disease, which consists of carriers, unidentified cases, and subclinical cases. The floating tip represents what the doctor sees at his office, practice, hospital, etc. The remaining Large Hidden area of the iceberg represents the majority of undetected illness in the community.

• The tip of the Iceberg is the diagnosis of the disease or the apparent infection.
  • The tip is of concern to the physician.
  • Unhealthy or diseased
  • Diagnostic test
• The hidden portion covers the people who are undiagnosed, or they are asymptomatic.
  • The hidden portion of the Iceberg is of concern to the epidemiologist.
  • Apparently healthy (no signs/symptoms, but the pathogenesis has started in the body)
  • Screening test
• The water around the Iceberg represents the healthy population.
• The line of demarcation separates the area of apparent infection from the inapparent infection.
• Diseases that follow the Iceberg phenomenon are
  • Non-communicable diseases.
  • Cancer.
  • Protein energy malnutrition cases.
  • Tuberculosis.
  • HIV
• Diseases that don't follow the Iceberg phenomenon are.
  • Measles
  • Rubella
  • Rabies
  • Tetanus

Sullivan index

• Also called as DFLE (Disability Free Life Expectancy)

DALY (Disability Adjusted Life Years)

• Years lost due to disability / premature death 
• Best Indicator of disease burden in a society

Incidence 

• No. of new cases per 1000 total population at risk
• It is a type of rate

Prevalence

Prevalence=total cases (new+old cases)/total population*100

• It is a proportion, always expressed in percentage

Types Of Surveillance

1. Passive (90%): Patient reports to health system on its own 
2. Active (8-10%): Seen in Malaria/ Polio/ TB/ Kala azar/ Leprosy/ RNTCP/ NLEP
3. Sentinel: To identify Hidden/ Missing cases, seen in HIV. The trend of a disease can be known
   • All are secondary levels of prevention

Previous Year Questions

Q. Food poisoning is an example of? (FMGE Dec 2017)

A. Point source epidemic 

B. Propagated source epidemic 

C. Common source epidemic

D. Pandemic

Q. A well of contaminated water resulting in an epidemic of acute watery diarrhea is a typical example of? (FMGE June 2018)

A. Common source single exposure epidemic

B. Common source continuous exposure epidemic

C. Slow epidemic

D. Propagated epidemic

Q. On Republic Day, a camp was organized, and people were screened for HTN by checking BP and for DM by checking their BMI and blood sugar level, level of prevention is? (FMGE Dec 2019)

A. Primary 

B. Primordial  

C. Secondary

D. Tertiary

Q. A man came for a checkup after his father had a cerebrovascular accident due to hypertension. What type of prevention is this?       (FMGE Aug 2020)

A. Primordial

B. Primary

C. Secondary

D. Specific protection

Q. Interval between primary and secondary cases is known as?         (NEET 2018)

A. Serial interval

B. Generation time

C. Incubation time

D. Lead time

Q. Long term changes/ sequelae of a disease are seen in?                       (FMGE Aug 2020)

A. Secular trend of a disease

B. Cyclical trend of a disease

C. Disease changing its traits according to herd immunity in the population

D. Disease changing the symptoms as per seasons

Q. Counseling and Screening is done for Tuberculosis is an HIV positive patient at ICTC center (NACP program). This is which level of prevention?                                     (FMGE June 2022)

A. Primary

B. Secondary 

C. Primordial

D. Tertiary 

Q. TB sputum assessment comes under which type of mode of prevention?      (FMGE June 2022)

A. Primary 

B. Secondary 

C. Primordial 

D. Tertiary

Q. A person working in an industry lost his hand. He is unable to do his daily activities including writing and machine working. Which is an Impairment In this guy?(FMGE June 2022)

A. Accident in industry 

B. Can't do his machine work 

C. Loss of anatomical structure  

D. Unemployment

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