Epidemiology Practice Questions

Q: What does a relative risk of 1 indicate?

No association between exposure and outcome. ### Explanation **Why Option A is Correct:** Relative Risk (RR) is the ratio of the incidence of a disease among an exposed group to the incidence among an unexposed group ($RR = \frac{I_e}{I_u}$). * When **RR = 1**, the numerator (incidence in exposed) and denominator (incidence in unexposed) are equal. * This signifies that the risk of the outcome is identical in both groups, indicating **no association** between the exposure and the disease. The exposure is neither harmful nor protective. **Why Other Options are Incorrect:** * **Option B & D:** Type I ($\alpha$) and Type II ($\beta$) errors refer to the probability of rejecting or failing to reject a null hypothesis due to chance or sample size issues. While a p-value or confidence interval helps determine if an RR of 1 is statistically significant, the value of 1 itself specifically defines the "null" point of association, not the error type. * **Option C:** A strong correlation would be indicated by an RR significantly greater than 1 (positive association/risk factor) or significantly less than 1 (negative association/protective factor). **NEET-PG High-Yield Pearls:** * **RR > 1:** Positive association (Exposure is a risk factor). * **RR < 1:** Negative association (Exposure is a protective factor, e.g., vaccines). * **Study Design:** RR is primarily calculated in **Cohort Studies** (prospective), whereas Odds Ratio (OR) is used for Case-Control studies. * **Attributable Risk (AR):** If RR = 1, then AR is 0, meaning zero percent of the disease is attributed to the exposure. * **Confidence Interval (CI):** If the 95% CI for RR includes the value **1** (e.g., 0.8 to 1.5), the results are not statistically significant.

Q: In a case-control study, the association between a disease and a risk factor is studied by which measure?

Odds ratio. In a **Case-Control Study**, we start with the outcome (disease) and look backward in time to determine exposure. Because the researcher determines the number of cases and controls, the true **Incidence** of the disease cannot be calculated. Since Relative Risk requires incidence data, it cannot be used here. Instead, we use the **Odds Ratio (OR)**, which estimates the strength of association by comparing the odds of exposure among cases to the odds of exposure among controls. ### Why the other options are incorrect: * **A. Relative Risk (RR):** This is the ratio of incidence among the exposed to incidence among the unexposed. It is the hallmark measure for **Cohort Studies**, where we follow a group forward in time to observe new cases. * **B. Attributable Risk (AR):** This measures the amount of disease incidence that can be attributed to a specific exposure (Incidence in exposed - Incidence in unexposed). Like RR, it requires incidence data from **Cohort Studies**. * **C. Population Attributable Risk (PAR):** This indicates how much the disease incidence in the total population would decrease if the exposure were eliminated. It also requires incidence data. ### High-Yield Clinical Pearls for NEET-PG: * **Odds Ratio** is also known as the **Cross-product ratio**. * If a disease is rare (Incidence < 5%), the Odds Ratio becomes a very good approximation of the Relative Risk. * **Case-Control Studies** are the design of choice for **rare diseases** or diseases with long latency periods. * **Recall Bias** is the most common systematic error encountered in Case-Control studies.

Q: Which of the following infections is not documented to be spread by sexual contact?

Hepatitis E Virus (HEV). ### Explanation The correct answer is **Hepatitis E Virus (HEV)**. **1. Why Hepatitis E (HEV) is the correct answer:** Hepatitis E is primarily transmitted via the **fecal-oral route**, most commonly through contaminated drinking water. Unlike other hepatitis viruses, there is currently **no documented evidence** of HEV transmission through sexual contact. It is characterized by epidemic outbreaks in developing countries and carries a high mortality rate (up to 20%) specifically in pregnant women. **2. Why the other options are incorrect:** * **Hepatitis B (HBV):** This is a classic sexually transmitted infection (STI). It is found in high concentrations in blood, semen, and vaginal secretions. Sexual contact is a major route of transmission globally. * **Hepatitis C (HCV):** While primarily blood-borne (parenteral), sexual transmission of HCV is documented, particularly among men who have sex with men (MSM) and individuals with multiple sexual partners or co-infection with HIV. * **Hepatitis A (HAV):** Although primarily fecal-oral, HAV is well-documented to spread via **sexual contact**, specifically through oral-anal contact (anilingus). Outbreaks are frequently reported in the MSM community. **3. NEET-PG High-Yield Pearls:** * **Vowels (A & E):** Transmitted by the **Enteric** route (Fecal-oral). * **Consonants (B, C, D):** Transmitted by **Blood** and Body fluids (Parenteral/Sexual). * **Exception to remember:** While both A and E are enteric, **only A** is significantly associated with sexual transmission (oral-anal). * **Pregnancy & HEV:** Always remember the association of HEV with **Fulminant Hepatic Failure** in the third trimester of pregnancy. * **HCV:** Has the highest risk of progressing to **chronic** hepatitis and cirrhosis.

Q: What is the most common carcinoma in females worldwide?

Breast. **Explanation:** The correct answer is **Breast Cancer**. According to the latest **GLOBOCAN** data (World Health Organization), breast cancer has overtaken lung cancer to become the most commonly diagnosed cancer globally, regardless of gender, and remains the **most common carcinoma in females worldwide**. **Why Breast Cancer is Correct:** Breast cancer accounts for approximately 1 in 4 cancer cases among women globally. Its high incidence is attributed to changing reproductive patterns (late age at first childbirth, fewer children), sedentary lifestyles, and increased screening/early detection in developed nations. **Analysis of Incorrect Options:** * **Cervix:** While cervical cancer remains a leading cause of cancer death in low-income countries and was historically the most common in India, it has been surpassed by breast cancer in most urban Indian registries and globally due to improved screening (Pap smears) and HPV vaccination. * **Lung:** Lung cancer is the leading cause of cancer-related *mortality* worldwide (both sexes combined) and the second most common cancer in women globally, but it ranks below breast cancer in terms of incidence. * **Kidney:** Renal cell carcinoma is significantly less common than breast, lung, or colorectal cancers in females. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cancer (Worldwide):** Breast Cancer (Incidence); Lung Cancer (Mortality). * **Most common cancer (India - Females):** Breast Cancer (followed by Cervix). * **Most common cancer (India - Males):** Lip/Oral Cavity (followed by Lung). * **Most common cancer (India - Both sexes):** Breast Cancer. * **Screening:** Mammography is the gold standard for breast cancer screening (starting age 40–50 years).

Q: Transmission of hepatitis A virus occurs:

2 weeks after onset of symptoms. **Explanation:** The transmission of Hepatitis A Virus (HAV) is primarily through the **fecal-oral route**. The period of maximum infectivity occurs during the late incubation period and the prodromal phase, when viral shedding in the feces is at its peak. **Why Option C is correct:** According to standard epidemiological data (and Park’s Textbook of Preventive and Social Medicine), the period of communicability for Hepatitis A is defined as **two weeks before the onset of jaundice to two weeks after the onset of symptoms**. While viral shedding decreases significantly once jaundice appears, the virus can still be detected in stools for up to two weeks, making this the clinically accepted window for transmission risk. **Analysis of Incorrect Options:** * **Option A & D:** These are partially correct but incomplete. While shedding occurs one week after symptoms, the risk persists for a full two weeks. * **Option B:** This only accounts for the pre-icteric phase. While this is the period of *maximum* infectivity, it does not cover the entire duration of transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–50 days (Average: 28 days). * **Maximum Infectivity:** Occurs **before** the onset of jaundice (during the late incubation period). By the time jaundice is clinically evident, the risk of transmission actually begins to decline. * **Secondary Attack Rate (SAR):** High among household contacts. * **Control:** Handwashing and the HAV vaccine are the mainstays. The vaccine is an inactivated (killed) vaccine given in two doses. * **Diagnosis:** Acute infection is confirmed by **Anti-HAV IgM**. Anti-HAV IgG indicates past infection or immunity.

Q: What is the denominator of the crude death rate?

Mid-year population. **Explanation:** The **Crude Death Rate (CDR)** is the simplest and most common measure of mortality in a population. It is defined as the number of deaths per 1,000 population in a given year. **1. Why Mid-year population is correct:** The denominator for CDR is the **Mid-year population** (the population as of July 1st of that year). This is used because the population size changes throughout the year due to births, deaths, and migration. The mid-year population serves as an estimate of the "average" population at risk during that period. * **Formula:** $\frac{\text{Total deaths during the year}}{\text{Mid-year population}} \times 1000$ **2. Why other options are incorrect:** * **Option A (1000 live births):** This is the denominator for the **Infant Mortality Rate (IMR)** and Maternal Mortality Ratio (MMR), not the general death rate. * **Option C (Total number of deaths):** This is the numerator of the CDR, not the denominator. * **Option D (Total number of cases):** This is typically the denominator for **Case Fatality Rate (CFR)**, which measures the killing power of a specific disease. **3. High-Yield Pearls for NEET-PG:** * **"Crude"** means the rate is not adjusted for factors like age or sex distribution. Therefore, it cannot be used for direct comparison between two different populations with different age structures. * For comparing mortality between two countries, **Age-Standardized Death Rates** are the preferred indicator. * The Mid-year population is also the denominator for the **Crude Birth Rate (CBR)**. * In India, the Sample Registration System (SRS) is the primary source for CDR data.

Q: What is the study design of choice for determining the diurnal variation of fat content in expressed breast milk for preterm babies?

Cross-sectional study. ### Explanation **Why Cross-sectional Study is Correct:** A cross-sectional study (also known as a **prevalence study**) is designed to examine the relationship between variables at a **single point in time** or over a short, defined interval. In this scenario, the objective is to measure the fat content in breast milk at specific times of the day (diurnal variation). Since the researchers are "taking a snapshot" of the milk composition at various points (e.g., morning vs. evening) without following the subjects over a long period to see an outcome, it fits the definition of a cross-sectional design. It is the most efficient way to determine the **prevalence or status** of a physiological parameter at a specific moment. **Analysis of Incorrect Options:** * **Prospective Cohort Study:** This involves following a group of exposed and unexposed individuals over time to see who develops a disease. It is used to determine **incidence and relative risk**, which is not the goal here. * **Ambispective Cohort Study:** This combines retrospective (past records) and prospective (future follow-up) data. It is unnecessarily complex for measuring a physiological baseline like milk fat. * **Case-Control Study:** This is a retrospective study that starts with an outcome (disease) and looks back for exposures. Since there is no "disease" or "control" group being compared for risk factors, this design is inapplicable. **High-Yield Pearls for NEET-PG:** * **Snapshot Rule:** If the study measures "What is happening right now?" it is Cross-sectional. * **Sequence:** Cross-sectional studies are often the first step in exploring a hypothesis before committing to a longitudinal cohort. * **Breast Milk Fact:** Fat is the most variable macronutrient in breast milk; it typically increases as the breast is emptied (hindmilk > foremilk) and often shows a diurnal peak in the evening.

Question 1

What does a relative risk of 1 indicate?

Accepted Answer

No association between exposure and outcome

Answer

The effect may be due to Type I error

Answer

A strong correlation between exposure and outcome

Answer

The effect may be due to Type II error

Question 2

In a case-control study, the association between a disease and a risk factor is studied by which measure?

Accepted Answer

Odds ratio

Answer

Relative risk

Answer

Attributable risk

Answer

Population attributable risk

Question 3

Which of the following infections is not documented to be spread by sexual contact?

Accepted Answer

Hepatitis E Virus (HEV)

Answer

Hepatitis A Virus (HAV)

Answer

Hepatitis B Virus (HBV)

Answer

Hepatitis C Virus (HCV)

Question 4

What is the most common carcinoma in females worldwide?

Accepted Answer

Breast

Answer

Cervix

Answer

Lung

Answer

Kidney

Question 5

Transmission of hepatitis A virus occurs:

Accepted Answer

2 weeks after onset of symptoms

Answer

One week before and one week after onset of symptoms

Answer

2 weeks before onset of symptoms

Answer

1 week after onset of symptoms

Question 6

Intraspecies competition refers to competition among what?

Accepted Answer

Individuals of a population

Answer

Species

Answer

Individuals of a community

Answer

Populations and their regulatory factors

Question 7

What is the denominator of the crude death rate?

Accepted Answer

Mid-year population

Answer

1000 live births

Answer

Total number of deaths in a community

Answer

Total number of cases in a community

Question 8

Which one of the following is not associated with an increased risk of cancer?

Accepted Answer

Excess fibre

Answer

Smoking

Answer

Alcohol

Answer

Chewing betel

Question 9

Which of the following statements about DOTS is INCORRECT?

Accepted Answer

None of the above.

Answer

Continuation phase drugs are given in a multi-blister combipack.

Answer

Medication is to be taken in the presence of a health worker.

Answer

Treatment is given on alternate days.

Question 10

What is the study design of choice for determining the diurnal variation of fat content in expressed breast milk for preterm babies?

Accepted Answer

Cross-sectional study

Answer

Prospective cohort study

Answer

Ambispective cohort study

Answer

Case-control study

Epidemiology — MCQs

Epidemiology — MCQs

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