Infectious Diseases Practice Questions

Q: Cluster testing is useful in detecting cases of which of the following?

Sexually transmitted infections. **Explanation:** **Cluster testing** (also known as contact tracing or partner notification) is a specialized epidemiological technique used to identify infected individuals by investigating the social and sexual networks of a known index case. **1. Why Sexually Transmitted Infections (STIs) is correct:** STIs do not occur randomly in a population; they tend to occur in "clusters" among individuals sharing common risk behaviors or sexual networks. In cluster testing, once a case is diagnosed, the investigator identifies and tests their sexual partners and social contacts (the cluster). This is the most effective way to break the chain of transmission for infections like Syphilis, Gonorrhea, and HIV, where asymptomatic carriers often unknowingly spread the disease. **2. Why other options are incorrect:** * **Measles:** This is a highly contagious respiratory infection spread via droplets. Control relies on **outbreak investigation** and mass immunization rather than tracing specific social clusters. * **Unimmunized/Immunized children (12-23 months):** To estimate immunization coverage, the WHO recommends the **30-cluster sampling technique**. This is a *sampling methodology* used for surveys to estimate prevalence/coverage in a community, which is distinct from "cluster testing" used for case-finding in infectious diseases. **High-Yield Pearls for NEET-PG:** * **Cluster Testing:** Best for STIs (Syphilis is the classic example). * **30-Cluster Sampling:** Used for EPI (Expanded Programme on Immunization) coverage surveys. It involves 30 clusters of 7 or 10 children each. * **Snowball Sampling:** A qualitative research method often used to reach "hidden populations" (e.g., IV drug users) which shares some conceptual similarities with cluster testing.

Q: What percentage of multidrug-resistant tuberculosis (MDR TB) cases are extensively drug-resistant tuberculosis (XDR TB) worldwide?

10%. ### Explanation **Correct Answer: B. 10%** **Understanding the Concept:** According to the World Health Organization (WHO) Global Tuberculosis Reports, approximately **10%** of all multidrug-resistant tuberculosis (MDR-TB) cases are estimated to be extensively drug-resistant (XDR-TB). * **MDR-TB** is defined as resistance to at least **Isoniazid (H) and Rifampicin (R)**, the two most potent first-line drugs. * **XDR-TB** (Revised WHO definition) is MDR-TB that is also resistant to any **fluoroquinolone** AND at least one additional Group A drug (such as **Bedaquiline or Linezolid**). The 10% figure represents a critical epidemiological threshold used to monitor the escalation of drug resistance globally. **Analysis of Incorrect Options:** * **Option A (5%):** This is an underestimate. While resistance patterns vary by region, the global average has consistently hovered around the 9-10% mark in recent surveillance data. * **Options C & D (20% and 25%):** These figures are significantly higher than the global average. While some "hotspots" (certain Eastern European or Central Asian countries) may report higher proportions, they do not represent the worldwide prevalence. **High-Yield NEET-PG Pearls:** * **Pre-XDR TB:** MDR-TB that is resistant to any fluoroquinolone (but not yet to Group A drugs). * **Primary vs. Acquired Resistance:** Most XDR-TB cases in high-burden countries are now due to **primary transmission** rather than poor treatment adherence alone. * **Treatment Duration:** Under the National TB Elimination Program (NTEP), the treatment for drug-resistant TB has shifted toward shorter, all-oral regimens (e.g., BPaLM regimen: Bedaquiline, Pretomanid, Linezolid, and Moxifloxacin). * **Diagnostic Gold Standard:** Cartridge Based Nucleic Acid Amplification Test (**CBNAAT/GeneXpert**) is the initial investigation of choice to detect Rifampicin resistance.

Q: Which of the following parasitic infections is characterized by a cyclodevelopmental stage?

Filaria. In vector-borne diseases, the relationship between the parasite and the vector is classified based on whether the parasite multiplies or undergoes structural changes within the host. **Explanation of the Correct Answer:** **Filaria (Option B)** is the classic example of **Cyclodevelopmental** transmission. In this stage, the parasite undergoes essential developmental changes (e.g., microfilariae maturing into L1, L2, and infective L3 larvae) within the mosquito vector, but there is **no multiplication** in numbers. One microfilaria ingested results in only one infective larva. **Analysis of Incorrect Options:** * **Malaria (Option A):** Exhibits **Cyclo-propagative** transmission. The *Plasmodium* parasite undergoes both developmental changes (gametocyte to sporozoite) and significant multiplication (sporogony) within the female Anopheles mosquito. * **Plague (Option C):** Exhibits **Propagative** transmission. The *Yersinia pestis* bacteria simply multiply within the gut of the rat flea without undergoing any cyclic changes or metamorphosis. * **Cholera (Option D):** This is a water-borne/fecal-oral disease, not a vector-borne parasitic infection. It does not involve biological transmission through an arthropod vector. **High-Yield Clinical Pearls for NEET-PG:** 1. **Propagative:** Multiplication only (e.g., Plague, Yellow Fever, Dengue). 2. **Cyclodevelopmental:** Development only; no multiplication (e.g., Filaria, Guinea worm). 3. **Cyclo-propagative:** Both development and multiplication (e.g., Malaria). 4. **Transovarial Transmission:** When the pathogen is passed to the next generation of vectors via eggs (e.g., Scrub typhus/Trombiculid mites, Kyasanur Forest Disease/Ticks).

Q: An extraordinary outbreak of SARS occurred in 2002-2003 and eventually resulted in 8096 recognized cases. All of the following are TRUE about SARS, EXCEPT:

Epidemic in India. **Explanation:** The 2002-2003 SARS (Severe Acute Respiratory Syndrome) outbreak was a significant global health event caused by the SARS-associated coronavirus (SARS-CoV). **1. Why Option A is the Correct Answer (The Exception):** While SARS was a global pandemic affecting 26 countries, it **never reached epidemic proportions in India**. India reported only 3 laboratory-confirmed cases and no deaths during the entire 2002-2003 period. Therefore, labeling it an "epidemic in India" is factually incorrect. **2. Analysis of Other Options:** * **Option B (Spreads by droplet):** This is true. The primary mode of transmission for SARS-CoV is through respiratory droplets (coughing or sneezing) and close person-to-person contact. * **Option C (Diagnosed by PCR):** This is true. Molecular testing via Reverse Transcription-Polymerase Chain Reaction (RT-PCR) is the gold standard for detecting the viral RNA in respiratory secretions, blood, or stool. * **Option D (Caused by SARS CoV):** This is true. The causative agent was identified as a novel coronavirus, later named SARS-CoV (a lineage B betacoronavirus). **High-Yield Clinical Pearls for NEET-PG:** * **Origin:** First emerged in Guangdong Province, China (November 2002). * **Intermediate Host:** The Himalayan palm civet was identified as the intermediate host, while horseshoe bats are the natural reservoirs. * **Case Fatality Rate (CFR):** Approximately 9.6% globally. * **Super-spreaders:** A unique epidemiological feature of SARS where certain individuals infected a disproportionately large number of contacts. * **Incubation Period:** Typically 2 to 7 days (up to 10 days).

Q: What is the epidemiological marker of Hepatitis B?

HBsAg. ### Explanation **Hepatitis B Surface Antigen (HBsAg)** is the correct answer because it is the first serological marker to appear in the blood after infection (even before symptoms or biochemical changes). In epidemiological studies, HBsAg is used to determine the **prevalence** of HBV in a population and to identify both acute and chronic carriers. Its presence for more than 6 months defines a chronic carrier state. **Analysis of Incorrect Options:** * **Anti-HBs (HBsAb):** This antibody indicates **immunity** to HBV, either through successful vaccination or recovery from a natural infection. It is not used as a marker for active disease prevalence. * **Anti-HBc (HBcAb):** This is a marker of **exposure**. IgM anti-HBc indicates recent/acute infection (and is the only marker positive during the "window period"), while IgG anti-HBc indicates past exposure. * **HBeAg:** This is a marker of **active viral replication and high infectivity**. While clinically significant for assessing the risk of transmission, it is not the primary epidemiological tool for screening populations. **High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The interval when HBsAg disappears but Anti-HBs has not yet appeared. **IgM anti-HBc** is the diagnostic marker here. * **Screening:** HBsAg is the standard marker for screening blood donors. * **Vaccine Response:** A person vaccinated against HBV will be **Anti-HBs positive** but **Anti-HBc negative** (since the vaccine contains only the surface antigen). * **Infectivity:** HBeAg and HBV-DNA levels are the best indicators of a patient's level of infectivity.

Question 1

What are the mechanisms by which cholera might be maintained during the intervals between peak cholera seasons?

Accepted Answer

Continuous transmission in man

Answer

Carrier status in animals

Answer

Carrier status in man

Answer

An environmental reservoir

Question 2

Cluster testing is useful in detecting cases of which of the following?

Accepted Answer

Sexually transmitted infections

Answer

Measles

Answer

Unimmunized children

Answer

Completely immunized children in the age group 12-23 months

Question 3

All of the following are true for Hepatitis B EXCEPT one?

Accepted Answer

Vertical transmission is more important than horizontal transmission.

Answer

Age of onset determines the prognosis.

Answer

The period of communicability lasts several months.

Answer

The virus can be found in the blood one month before the onset of jaundice.

Question 4

What is the method of choice for mass screening of tuberculosis?

Accepted Answer

Sputum smear examination by direct microscopy

Answer

Tuberculin test

Answer

Mass Miniature Radiography (MMR)

Answer

Sputum culture

Question 5

What percentage of multidrug-resistant tuberculosis (MDR TB) cases are extensively drug-resistant tuberculosis (XDR TB) worldwide?

Accepted Answer

10%

Answer

5%

Answer

20%

Answer

25%

Question 6

Which of the following conditions is known to be transmitted vertically?

Accepted Answer

Herpes simplex

Answer

Leprosy

Answer

Tetanus

Answer

Whooping cough

Question 7

Which of the following parasitic infections is characterized by a cyclodevelopmental stage?

Accepted Answer

Filaria

Answer

Malaria

Answer

Plague

Answer

Cholera

Question 8

Which of the following statements about hepatitis B is FALSE?

Accepted Answer

Vertical transmission is more important than horizontal transmission.

Answer

The communicable period lasts for months.

Answer

The virus can be found in the blood 1 month before jaundice appears.

Answer

The age of onset determines the prognosis.

Question 9

An extraordinary outbreak of SARS occurred in 2002-2003 and eventually resulted in 8096 recognized cases. All of the following are TRUE about SARS, EXCEPT:

Accepted Answer

Epidemic in India

Answer

Spreads by droplet

Answer

Diagnosed by PCR

Answer

Caused by SARS CoV

Question 10

What is the epidemiological marker of Hepatitis B?

Accepted Answer

HBsAg

Answer

Anti-HBs

Answer

Anti-HBc

Answer

HBeAg

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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