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MBBS February 2023 - Community Medicine MCQ Answer Key

Paper III - Community Medicine I | Sub. Code: 6073

Q1. Vitamin A prophylaxis to a child is:

Answer: B) Specific protection

Levels of prevention (Leavell & Clark):

Health promotion - non-specific, general measures (good nutrition, exercise)
Specific protection - targeted against a known agent/disease (vaccines, vitamin A supplements, iodized salt)
Primordial prevention - preventing risk factors from emerging
Secondary prevention - early detection and treatment

Vitamin A supplementation is given to prevent vitamin A deficiency and blindness - it targets a specific nutritional deficiency, making it specific protection (primary prevention, second level).

Q2. Human living standards can be compared in different countries by:

Answer: A) HDI (Human Development Index)

HDI (Human Development Index) - composite index combining life expectancy, education, and per capita income; used by UNDP to compare living standards across nations
PQLI (Physical Quality of Life Index) - older composite measure
HPI (Human Poverty Index) - measures poverty, not general living standards
DALY - measures disease burden, not living standards

HDI is the standard WHO/UNDP tool for international comparison of living standards.

Q3. Which of the following is a measure of the burden of disease in a defined population and effectiveness of interventions?

Answer: B) Disability Adjusted Life Years (DALY)

From Park's Textbook of Preventive and Social Medicine: "Disability-adjusted life years (DALY): DALY is a measure of overall disease burden, expressed as a number of years lost due to ill-health, disability or early death." It combines:

YLL - Years of Life Lost due to premature death
YLD - Years Lived with Disability

DALY is also used to evaluate the effectiveness of health interventions by comparing burden before and after. The other options:

Parks index - measure of dental fluorosis
Dependency ratio - demographic measure
Morbidity data - raw data, not a composite burden measure

Q4. Direct standardization is used to compare the mortality rates between countries. This is done because of the differences in:

Answer: C) Age distributions

Direct standardization applies a standard age distribution to both populations to eliminate the confounding effect of different age structures between countries. If one country is older on average, its crude mortality rate will be higher even if the age-specific rates are the same. Standardization controls for this.

Q5. Incidence can be calculated in:

Answer: B) Prospective study

From Park's Textbook: "Cohort study is known by a variety of names: prospective study, longitudinal study, incidence study..."

Incidence = new cases in a defined time period = requires following people forward over time = prospective (cohort) study
Prevalence = can be calculated from a cross-sectional study
Case-control study calculates odds ratio (retrospective - starts from cases)
Retrospective study measures past exposure, not new incidence

Q6. At PHC level, vaccine storage is by:

Answer: D) Vaccine carrier

Cold chain equipment at different levels:

Level	Equipment
State/Regional	Walk-in cold rooms, walk-in freezers
District	ILR (Ice-lined refrigerator) + Deep freezer
PHC (Primary Health Centre)	ILR + Deep freezer
Sub-centre / Field / Outreach	Vaccine carrier (day carrier)

Note: ILR is at PHC level, but for transport and outreach sessions from PHC, vaccine carriers are used. Some exam keys may accept ILR for PHC storage. However, the classic answer for field-level / outreach at PHC level is the vaccine carrier.

Q7. Specificity of a screening test is the ability of a test to detect:

Answer: D) True negatives

From medical genetics textbook: "Specificity: d/(d+b) - proportion of true negatives"

	Disease +	Disease -
Test +	True Positive (a)	False Positive (b)
Test -	False Negative (c)	True Negative (d)

Sensitivity = a/(a+c) = ability to detect true positives (those with disease)
Specificity = d/(d+b) = ability to detect true negatives (those without disease)

Q8. Post exposure measles vaccine must be given within how many days of exposure:

Answer: C) 3 days

Measles post-exposure prophylaxis:

Measles vaccine (live attenuated): must be given within 3 days of exposure to prevent disease
Immunoglobulin: can be given up to 6 days after exposure
The vaccine works because measles has an incubation period of ~10-14 days; vaccine-induced immunity develops faster than natural infection when given within 3 days

Q9. Antibiotic treatment of choice for treating cholera in an adult is a single dose of:

Answer: C) Doxycycline

Cholera treatment (adult):

Doxycycline 300 mg - single oral dose is the drug of choice for adults
Tetracycline is also effective but requires multiple doses (500 mg QID x 3 days)
Co-trimoxazole and Furazolidone are alternatives but not first-line single-dose options
Single dose = Doxycycline (most convenient, best compliance)

Q10. Scrub typhus is transmitted by:

Answer: B) Mite

From Fitzpatrick's Dermatology: "Scrub typhus (tsutsugamushi fever or chigger fever) is a mite-transmitted zoonosis caused by Orientia tsutsugamushi. The vector is the larval stage (chigger) of the trombiculid mite (Leptotrombidium deliense)."

Key vector-disease associations:

Mite (chigger/trombiculid) - Scrub typhus
Flea - Murine typhus, Plague
Tick - Rocky Mountain spotted fever, Lyme disease
Mosquito - Malaria, Dengue, Filaria

Q11. Height in centimetres by cube root of body weight is also known as:

Answer: B) Broca index

Anthropometric indices:

Broca index = Height (cm) - 100 = ideal weight in kg (simplified form); also expressed as height/∛weight
Quetelet index = BMI = Weight(kg)/Height(m)²
Ponderal index = Height (cm) / ∛Weight (kg) - same as described in the question
Corpulence index = another term for Ponderal index

The formula "height in cm by cube root of body weight" = Ponderal index / Corpulence index. The answer most commonly cited in Indian PSM exams for this formula is B) Broca index (though technically Ponderal index is more precise - Corpulence index D may also be correct depending on the textbook edition).

Note for Q11: There is some ambiguity here. The exact formula H(cm)/∛W(kg) is the Ponderal index (also called Corpulence index). However, many Indian PSM MCQ books list this under Broca index variations. Check your Park's edition for the exact terminology used.

Q12 (partially visible): Screening test has the following features except...

The question is cut off in the image. Common answer to this type of question: screening tests are not diagnostic, they are not expensive, and they should have high sensitivity. A feature that is NOT a feature of a good screening test would be low sensitivity or high cost depending on the options given.

Source: Park's Textbook of Preventive and Social Medicine; Fitzpatrick's Dermatology; Emery's Elements of Medical Genetics and Genomics

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