Infectious Diseases Practice Questions

Q: Negative Mantoux test is when induration is:

<5mm. **<5mm** - A **Mantoux test** (tuberculin skin test) result of less than 5mm induration is generally considered **negative** in all populations, indicating no evidence of M. tuberculosis infection. - However, interpretation can vary depending on the patient's risk factors; for some, induration <5mm would still be considered positive. For a generally healthy individual with no known risk factors, it is a definitive negative. *<15mm* - An induration of 15mm or more is usually considered a **positive** result in anyone, including those with no known risk factors for TB. - This threshold indicates a high likelihood of M. **tuberculosis infection**. *<20mm* - While an induration over 20mm is definitively positive, specifying "<20mm" as negative would incorrectly classify many positive results (e.g., 5-19mm) as negative. - The standard cut-off for a universally negative result is much lower than 20mm. *<10mm* - An induration between **5mm and 9mm** can be considered positive in certain high-risk groups (e.g., recent contacts of TB patients, immunocompromised individuals) and is not universally negative. - Therefore, a test result of "<10mm" does not solely define a negative test, as it might include positive results for some populations [1].

Q: A 17-year-old female presents with a history of fever and headache and now develops altered sensorium. CT scan shows basal exudates with meningeal enhancement. The CSF is most likely to show:

Lymphocytic pleocytosis, low sugar, high protein. ***Lymphocytic pleocytosis, low sugar, high protein*** - The combination of **fever, headache, altered sensorium**, and **basal exudates with meningeal enhancement** on CT is highly suggestive of **tuberculous meningitis (TBM)**. - TBM typically presents with **lymphocytic pleocytosis**, **low CSF glucose** due to bacterial metabolism, and **elevated CSF protein** due to increased permeability of the blood-brain barrier. *Lymphocytic pleocytosis, normal sugar, high protein* - While **lymphocytic pleocytosis** and **high protein** can be seen in viral meningitis or some chronic inflammatory conditions, **normal sugar** would make TBM less likely, as TBM characteristically causes significant hypoglycemia in the CSF. - This profile might be more consistent with conditions like **Guillain-Barré syndrome** or **neoplastic meningitis** where sugar remains normal. *Polymorphonuclear pleocytosis, normal sugar, high protein* - **Polymorphonuclear (neutrophilic) pleocytosis** is characteristic of **acute bacterial meningitis**, not TBM. - While TBM can sometimes show a mixed picture or early neutrophilic predominance, a purely PMN dominance would point away from TBM. *Lymphocytic pleocytosis, low sugar, low protein* - A **low CSF protein** with **low sugar** and **lymphocytic pleocytosis** is an unusual combination and generally not seen in any specific meningitis type. - While **low sugar** and **lymphocytic pleocytosis** are typical of TBM, **low protein** is not; protein is almost always elevated in TBM.

Q: All of the following are strongly associated with AIDS except:

ANUG. ***ANUG*** - **Acute necrotizing ulcerative gingivitis (ANUG)**, also known as Vincent stomatitis or "trench mouth," is a severe form of gingivitis caused by a bacterial infection. While it can occur in immunocompromised individuals, it is not considered an AIDS-defining illness [1]. - ANUG is characterized by painful, bleeding gums, foul breath, and ulceration of the interdental papillae, but its mere presence does not automatically indicate an AIDS diagnosis [1]. *Candidiasis* - **Candidiasis**, particularly **esophageal candidiasis**, is an **AIDS-defining illness** and strongly associated with advanced HIV infection [1]. - Oral candidiasis (thrush) is also very common in HIV-positive individuals and often progresses to esophageal involvement as the immune system weakens [1]. *Kaposi sarcoma* - **Kaposi sarcoma** is an **AIDS-defining cancer** caused by **human herpesvirus 8 (HHV-8)**, and its presence strongly indicates advanced HIV disease [1]. - It manifests as vascular lesions on the skin, mucous membranes, and internal organs, and its incidence has decreased with effective antiretroviral therapy [1]. *Oral hairy leukoplakia* - **Oral hairy leukoplakia (OHL)** is a benign lesion caused by the **Epstein-Barr virus (EBV)**, commonly seen in HIV-positive individuals, signaling significant immunosuppression [1]. - While not an AIDS-defining condition itself, OHL is a strong indicator of **HIV disease progression** and impaired immune function [1].

Q: What is the most common extra-intestinal complication of Shigellosis?

Reactive arthritis. ***Reactive arthritis*** - **Reactive arthritis** is triggered by a prior infection, such as *Shigellosis*, and is the most common extra-intestinal complication, especially in HLA-B27 positive individuals [1]. - It typically presents with a triad of **arthritis**, **urethritis**, and **conjunctivitis**, though not all symptoms may be present [1]. *Pneumonia* - While pneumonia can occur in severely ill patients, it is not a common nor specific extra-intestinal complication directly linked to the pathogenesis of *Shigellosis*. - Respiratory complications are rare in uncomplicated cases of shigellosis. *Meningitis* - **Meningitis** is a rare and severe complication, primarily seen in young children or immunocompromised individuals, and is not the most common extra-intestinal manifestataion. - It suggests systemic spread of the bacteria beyond the gastrointestinal tract, which is uncommon. *HUS* - **Hemolytic Uremic Syndrome (HUS)** is a well-known complication of *E. coli* O157:H7 (Shiga toxin-producing E. coli, STEC), rather than *Shigella* species. - While some *Shigella* strains produce Shiga toxin, HUS is far less common in *Shigellosis* compared to STEC infections.

Q: A lady presented with fever and rashes. She returned from the USA and gives a history of exposure to ticks. Most probable diagnosis is

Rocky mountain fever. ***Rocky mountain fever*** - **Rocky Mountain spotted fever (RMSF)** is a **tick-borne disease** caused by the bacterium *Rickettsia rickettsii*, characterized by **fever and rash**. - The patient's history of returning from the **USA** and **tick exposure** in the context of fever and rash makes RMSF the most probable diagnosis, as it is endemic to many regions of the Americas. *Oraya fever* - **Oraya fever** is caused by **Bartonella bacilliformis** and is characterized by acute hemolytic anemia and fever, with a rash appearing later in some cases. - It is geographically restricted to **Andean regions of Peru, Ecuador, and Colombia**, making it unlikely for a patient returning from the USA. *Scrub typhus* - **Scrub typhus** is a **mite-borne disease** caused by *Orientia tsutsugamushi*, presenting with fever, rash, and often an **eschar** [1]. - It is endemic to **Asia, Australia, and the Pacific Islands**, not typically associated with exposure in the USA [1]. *Epidemic typhus* - **Epidemic typhus** is caused by **Rickettsia prowazekii** and is typically transmitted by the **human body louse**, occurring in crowded, unsanitary conditions. - While it presents with fever and rash, the mode of transmission and typical epidemiological context (lice, crowded living) do not fit the presented case of tick exposure in the USA.

Q: Most common single cause of pyrexia of unknown origin

Mycobacterium tuberculosis. ***Mycobacterium tuberculosis*** - **Tuberculosis** (TB) is a common cause of **Pyrexia of Unknown Origin (PUO)** [2], especially in endemic areas, often presenting with fever, weight loss, and night sweats [3], [4]. - The fever in TB can be **intermittent** and **debilitating**, making diagnosis challenging without specific investigations like cultures or biopsies [1]. *Salmonella paratyphi* - This bacterium causes **paratyphoid fever**, which can present with prolonged fever similar to typhoid, but it is less common globally as a single cause of PUO compared to TB. - While it can manifest as a persistent fever, other characteristic symptoms like rash or gastrointestinal issues might be present, making it less "unknown" in some contexts. *Brucella* - **Brucellosis** (Malta fever) is characterized by **undulating fever**, arthralgia, and fatigue, but infections are often linked to exposure to infected animals or unpasteurized dairy products, limiting its prevalence as the *most common single* PUO cause. - Diagnosis requires specific serological tests or cultures, but its geographical distribution and transmission routes make it less globally pervasive than TB. *Salmonella typhi* - **Typhoid fever**, caused by *Salmonella typhi*, is a significant cause of prolonged fever, but its typical presentation often includes specific symptoms like **relative bradycardia**, **rose spots**, and gastrointestinal symptoms, which might lead to an earlier diagnosis than a true PUO. - While it can cause prolonged, high fever, global incidence and the often-distinctive clinical picture prevent it from typically being labeled as the *most common single* cause of PUO.

Q: Young female with 3 days fever presents with headache, BP 90/60 mmHg, Heart rate of 114/min, and pin point spots developed distal to BP cuff. Most likely organism is:

N. meningitidis. ***N. meningitidis*** - The presentation of **fever**, **headache** [1], signs of **shock** (hypotension, tachycardia), and **petechiae/purpura** (pinpoint spots distal to BP cuff, indicating a bleeding disorder such as thrombocytopenia or DIC often associated with meningococcemia) is classic for **meningococcal sepsis**. - *Neisseria meningitidis* is well-known for causing **rapidly progressive sepsis with disseminated intravascular coagulation (DIC)** and a characteristic **petechial or purpuric rash**. *Brucella suis* - *Brucella suis* causes **brucellosis**, which typically presents with **undulating fever**, **arthralgia**, fatigue, and hepatosplenomegaly. - While it can cause systemic illness, it does not typically manifest with the acute, severe presentation of **sepsis** and **hemorrhagic rash** seen in this patient. *Staphylococcus aureus* - *Staphylococcus aureus* can cause widespread infections, including sepsis characterized by **fever**, **hypotension**, and **tachycardia**, often leading to **toxic shock syndrome**. [2] - However, while *S. aureus* can cause skin manifestations like cellulitis or abscesses, it is less commonly associated with the specific **petechial rash** in the context of acute sepsis, unless it's an endocarditis with septic emboli, which would have a different clinical scenario. [2] *Brucella abortus* - Similar to *Brucella suis*, *Brucella abortus* causes **brucellosis**, a chronic zoonotic infection. - The clinical picture of **acute fulminant sepsis with hemorrhagic skin lesions** is not characteristic of *Brucella abortus* infection.

Q: Early sign of tetanus is locked jaw due to early involvement of:

Masseter. ***Masseter*** - **Trismus**, or **locked jaw**, is one of the earliest and most characteristic signs of tetanus [1]. - It results from powerful and sustained **spasms** of the **masseter muscles**, which are the primary muscles responsible for closing the jaw. *Temporalis* - The **temporalis muscle** is also involved in jaw closure, but the **masseter** is often the first and most prominently affected in early tetanus, leading to the characteristic "locked jaw." - It is a fan-shaped muscle on the side of the skull, contributing to chewing. *Medial pterygoid* - The **medial pterygoid muscle** aids in jaw closure, protrusion, and side-to-side movements but is not typically the very first muscle to manifest severe spasms in tetanus. - Spasms in this muscle would contribute to trismus but usually follow the more direct impact on the masseters. *Lateral pterygoid* - The **lateral pterygoid muscle** is primarily responsible for opening the jaw and moving it side-to-side, rather than closing it. - Spasm of this muscle would cause the jaw to involuntarily open or deviate, which is contrary to the "locked jaw" symptom of tetanus.

Q: Early treatment failure in malaria is indicated by all, EXCEPT:

None of the options. Early treatment failure suggests the antimalarial regimen is ineffective and requires a change in therapy or further investigation into drug resistance, which has historically affected drugs like chloroquine and sulfadoxine-pyrimethamine [1]. *Parasitemia on day 3 >50% of day 1 count* - This criterion indicates inadequate clearance of parasites by the third day of treatment. - A significant reduction in parasite count is expected by day 3; if the count remains high (over 50% of the initial count), it suggests treatment failure. *Parasitemia on day 3 with temperature >37.5°C* - The persistence of fever along with parasitemia on day 3 signifies ongoing infection and a poor clinical response to treatment. - Effective antimalarial therapy should lead to a resolution of fever and a substantial decrease in parasite load by this time. *Development of danger signs or severe malaria on days 1, 2, 3 in presence of parasitemia* - The worsening of clinical condition to include danger signs or criteria for severe malaria within the first three days of treatment, in the presence of parasites, is a clear sign of treatment failure. - This indicates that the chosen therapy is not preventing disease progression and severe complications.

Q: Most common extra pulmonary involvement of TB ?

Lymph nodes. ***Bone*** - While **skeletal tuberculosis** can occur, particularly in the spine (**Pott's disease**), it is not the most common extrapulmonary manifestation [2]. - Bone involvement typically presents with localized pain, swelling, and sometimes neurological deficits [2]. *Ileocecal* - **Gastrointestinal TB**, especially involving the **ileocecal region**, is a significant form of extrapulmonary TB. - It often leads to abdominal pain, weight loss, and malabsorption, but it is less common than lymph node involvement. *Lymph nodes* - **Tuberculous lymphadenitis** (scrofula) is the **most common extrapulmonary manifestation of TB**, especially in immunocompetent individuals and children [1]. - Typically presents as painless, slowly enlarging lymph nodes, most often in the cervical region [1]. *Pleura* - **Pleural effusion** (tuberculous pleurisy) is a common manifestation of TB and involves the lining of the lungs. - Although frequent, it is generally considered a **pulmonary complication** or a contiguous spread from the lung rather than a distinctly extrapulmonary site like the lymph nodes.

Question 1

Negative Mantoux test is when induration is:

Accepted Answer

<5mm

Answer

<15mm

Answer

<20mm

Answer

<10mm

Question 2

A 17-year-old female presents with a history of fever and headache and now develops altered sensorium. CT scan shows basal exudates with meningeal enhancement. The CSF is most likely to show:

Accepted Answer

Lymphocytic pleocytosis, low sugar, high protein

Answer

Lymphocytic pleocytosis, normal sugar, high protein

Answer

Polymorphonuclear pleocytosis, normal sugar, high protein

Answer

Lymphocytic pleocytosis, low sugar, low protein

Question 3

All of the following are strongly associated with AIDS except:

Accepted Answer

ANUG

Answer

Candidiasis

Answer

Kaposi sarcoma

Answer

Oral hairy leukoplakia

Question 4

What is the most common extra-intestinal complication of Shigellosis?

Accepted Answer

Reactive arthritis

Answer

Pneumonia

Answer

Meningitis

Answer

HUS

Question 5

A lady presented with fever and rashes. She returned from the USA and gives a history of exposure to ticks. Most probable diagnosis is

Accepted Answer

Rocky mountain fever

Answer

Oraya fever

Answer

Scrub typhus

Answer

Epidemic typhus

Question 6

Most common single cause of pyrexia of unknown origin

Accepted Answer

Mycobacterium tuberculosis

Answer

Salmonella paratyphi

Answer

Brucella

Answer

Salmonella typhi

Question 7

Young female with 3 days fever presents with headache, BP 90/60 mmHg, Heart rate of 114/min, and pin point spots developed distal to BP cuff. Most likely organism is:

Accepted Answer

N. meningitidis

Answer

Brucella suis

Answer

Staphylococcus aureus

Answer

Brucella abortus

Question 8

Early sign of tetanus is locked jaw due to early involvement of:

Accepted Answer

Masseter

Answer

Temporalis

Answer

Medial pterygoid

Answer

Lateral pterygoid

Question 9

Early treatment failure in malaria is indicated by all, EXCEPT:

Accepted Answer

None of the options

Answer

Parasitemia on day 3 >50% of day 1 count

Answer

Parasitemia on day 3 with temperature >37.5°C

Answer

Development of danger signs or severe malaria on days 1, 2, 3 in presence of parasitemia

Question 10

Most common extra pulmonary involvement of TB ?

Accepted Answer

Lymph nodes

Answer

Bone

Answer

Ileocecal

Answer

Pleura

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?