Infectious Diseases Practice Questions

Q: A CSF/serum glucose ratio of < 0.4 is highly suggestive of:

Bacterial Meningitis. Bacterial Meningitis - A **CSF/serum glucose ratio of < 0.4** is a classic finding in bacterial meningitis, indicating that bacteria are consuming glucose in the CSF [1]. - This ratio, along with other CSF findings like **elevated protein** and **pleocytosis** (predominantly neutrophils), helps differentiate bacterial from other forms of meningitis [1]. *Viral Meningitis* - In viral meningitis, the **CSF glucose is typically normal** or only slightly decreased, leading to a normal to slightly decreased CSF/serum glucose ratio (usually > 0.6) [1]. - The cell count primarily shows a **lymphocytic predominance**, differentiating it from bacterial meningitis [1]. *Carcinomatous Meningitis* - While CSF glucose can be decreased in carcinomatous meningitis due to tumor cell metabolism, it is often **not as profoundly low** as in bacterial meningitis. - The diagnosis is usually confirmed by finding **malignant cells** in the CSF and/or imaging evidence of leptomeningeal spread. *Acanthamoeba meningitis* - **Acanthamoeba meningitis** is a rare and severe form of meningitis caused by a free-living amoeba, leading to meningoencephalitis. - While it can cause inflammatory changes and glucose consumption, a specific **CSF/serum glucose ratio of < 0.4** is not a hallmark and it is often associated with a granulomatous inflammatory response.

Q: The following about leptospirosis is true except?

Tetracycline is the drug of choice. ***Tetracycline is the drug of choice*** - While tetracyclines (e.g., **doxycycline**) can be used, the primary drug of choice for severe leptospirosis is typically **intravenous penicillin G** or **ceftriaxone**. - For milder cases, oral **doxycycline** or **amoxicillin** may be used, but labeling tetracycline as *the* drug of choice above penicillin for all severities is inaccurate. *Seen in sewage workers* - **Leptospirosis** is an occupational hazard for individuals exposed to contaminated water or soil, including **sewage workers**, farmers, and veterinarians [1]. - This is because the bacteria, *Leptospira*, are shed in the urine of infected animals and can survive in moist environments [1]. *High fever with chills* - The **initial phase** of leptospirosis (leptospiremic phase) commonly presents with **acute onset of high fever** and **chills**, along with headaches and myalgia [1]. - These are non-specific symptoms that can make early diagnosis challenging [1]. *Jaundice is present* - **Jaundice** is a characteristic symptom of severe leptospirosis, particularly in the form known as **Weil's disease**. - It indicates **hepatic involvement** and often accompanies other severe manifestations like renal dysfunction (leading to **oliguria** or **anuria**) and hemorrhage [1].

Q: In tuberculous meningitis, what is NOT seen:

Increased CSF glucose. ***Increased CSF glucose*** - In **tuberculous meningitis**, the meningeal inflammation and metabolic activity of the Mycobacterium tuberculosis consume glucose, leading to **decreased CSF glucose levels**, not increased. [1] - An increased CSF glucose level would be highly atypical and suggests an alternative diagnosis or a procedural error. *Turbidity of CSF* - **CSF turbidity** is a common finding in many forms of meningitis, including tuberculous meningitis, due to the presence of inflammatory cells and proteins. [1] - The appearance can range from opalescent to frankly purulent depending on the severity of inflammation. [2] *Increased lymphocytes* - **Tuberculous meningitis** is typically characterized by a **lymphocytic pleocytosis** in the CSF, meaning an increase in the number of lymphocytes. - This is a hallmark of chronic inflammatory processes affecting the central nervous system. *Decreased protein levels* - The inflammatory process in **tuberculous meningitis** leads to increased vascular permeability and protein leakage into the CSF, resulting in **elevated CSF protein levels**, not decreased. [2] - Decreased CSF protein levels would be an unusual finding in this condition.

Q: A microbiology laboratory reports growth of Staphylococcus aureus from pus drained from a breast abscess. What is the most likely condition predisposing the patient to the development of a breast abscess?

Breast feeding. ***Breast feeding*** - **Lactation** is the most common predisposing factor for breast abscesses, as **milk stasis** and **cracked nipples** can lead to bacterial entry and infection. - *Staphylococcus aureus* is the most frequent pathogen isolated in **lactational mastitis** and subsequent abscess formation. *Endocarditis* - Endocarditis is an infection of the **heart valves** and, while it can cause septic emboli, it is not a direct predisposing factor for a localized breast abscess. - The primary symptoms of endocarditis are usually systemic, such as fever, new heart murmurs, and embolic phenomena, which are not described here. *Menopause* - Menopause involves hormonal changes that can affect breast tissue but typically does not predispose women to acute bacterial breast abscesses. - Postmenopausal breast infections are less common and often associated with duct ectasia or other benign conditions rather than acute abscesses from *Staphylococcus aureus*. *Inflammatory breast carcinoma* - Inflammatory breast carcinoma can mimic infection with redness and warmth, but it is a **malignancy** and does not directly predispose to a bacterial abscess. - While it can sometimes be superimposed on an infection or cause skin changes that increase infection risk, it is not the most direct predisposing condition for a *Staphylococcus aureus* abscess.

Q: In bacterial meningitis, CSF has:

High protein. High protein - In bacterial meningitis, inflammation and increased permeability of the blood-brain barrier lead to significant leakage of plasma proteins into the cerebrospinal fluid (CSF), resulting in elevated CSF protein levels [1]. - This is a hallmark finding due to the breakdown of normal barrier function and the presence of bacterial exudates [1]. *High glucose* - Bacterial meningitis is characterized by low CSF glucose because bacteria metabolize glucose for their growth and survival. - White blood cells also consume glucose, further decreasing its concentration in the CSF. *High lymphocytes* - While lymphocytes may be present, the predominant cell type in acute bacterial meningitis is neutrophils, indicating an acute inflammatory response [1]. - Lymphocyte predominance is typically seen in viral or chronic meningitis [2]. *High neutrophils* - High neutrophils are indeed characteristic of bacterial meningitis, reflecting the acute inflammatory response to bacterial pathogens [1]. - However, the question asks for a single characteristic, and while neutrophilic pleocytosis is prominent, elevated protein is another consistent and significant finding.

Q: A 40-year-old man presents with fever, productive cough, shortness of breath, mild confusion, and diarrhea. Ten days earlier, he used a shower in a public facility. Sputum Gram stain and direct fluorescent antibody testing are performed, and chest imaging is shown. Which laboratory abnormality is most likely?

Hyponatremia. ***Hyponatremia*** - **Legionella pneumonia** often causes syndrome of inappropriate antidiuretic hormone (SIADH) secretion, leading to **dilutional hyponatremia**. - **Gastrointestinal symptoms** like diarrhea, commonly associated with *Legionella* infection, can also contribute to electrolyte imbalances via fluid loss. *Hypocalcemia* - While electrolyte abnormalities can occur, **hypocalcemia** is not a classic or most common finding specifically associated with *Legionella* pneumonia. - It is more typically seen in conditions like **sepsis** or **acute pancreatitis**, which present differently. *Hypernatremia* - **Hypernatremia** indicates a deficit of total body water relative to total body sodium, which is less common in *Legionella* pneumonia, where **SIADH** typically leads to water retention. - Dehydration can cause hypernatremia, but the overall clinical picture of *Legionella* pneumonia and associated GI symptoms usually doesn't lead to this severe imbalance. *Hypercalcemia* - **Hypercalcemia** is a rare finding in acute infections and is generally not associated with *Legionella* pneumonia. - It is more characteristic of conditions like **malignancy** or **hyperparathyroidism**.

Q: Most common muscle involved in Tropical pyomyositis

Quadriceps. ***Quadriceps*** - The **quadriceps femoris muscle** is the most frequently affected muscle group in tropical pyomyositis, being involved in 30-50% of cases. - Its large muscle mass and susceptibility to minor trauma may contribute to its high incidence of involvement. *Triceps* - While other muscles can be affected, the **triceps muscle** is less commonly involved than the large muscles of the thigh in tropical pyomyositis. - Involvement of upper limb muscles is generally less frequent compared to lower limb and trunk muscles. *Biceps* - The **biceps muscle** is an infrequently affected site in tropical pyomyositis. - The disease typically shows a predilection for larger muscle groups in the lower limbs and trunk rather than the upper limbs. *Gluteus* - The **gluteal muscles** can be affected in tropical pyomyositis but are not as commonly involved as the quadriceps. - Involvement of the gluteal region is more likely to occur in disseminated disease or in specific risk groups.

Q: Six days after receiving several flea bites in a rat-infested shed, a homeless 24-year-old man develops fever, chills, and a rash that spreads from his abdomen to cover his extremities. He is seen at the hospital emergency department, where blood is drawn for analysis. Eight days later, the public health department reports the presence of antibody to one of the rickettsial group antigens. Which of the following is the most likely diagnosis?

Endemic typhus. ***Endemic typhus*** - The patient's history of exposure to a rat-infested shed and flea bites, followed by fever, chills, and a rash spreading from the abdomen to the extremities [1], is highly consistent with **endemic (murine) typhus** [1]. - **Endemic typhus** is caused by *Rickettsia typhi* and is transmitted by the **flea vector** with rats as the reservoir [1]. *Epidemic typhus* - **Epidemic typhus** is caused by *Rickettsia prowazekii* and is transmitted by the **human body louse**, typically in conditions of overcrowding and poor hygiene. - While it shares similar symptoms, the **flea bite** and **rat exposure** in this case point away from epidemic typhus. *Q fever* - **Q fever** is caused by *Coxiella burnetii* and is typically acquired through inhalation of **contaminated aerosols** from infected livestock (cattle, sheep, goats). - Symptoms usually include fever, headache, and flu-like illness, but a **rash is uncommon**, and the transmission vector (flea) is inconsistent with the patient's presentation. *Rocky Mountain spotted fever* - **Rocky Mountain spotted fever (RMSF)** is caused by *Rickettsia rickettsii* and is transmitted by **tick bites**. - The rash of RMSF typically starts on the **ankles and wrists** and spreads centrally, often involving the palms and soles, which differs from the described abdominal onset and flea vector.

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].

Question 1

A CSF/serum glucose ratio of < 0.4 is highly suggestive of:

Accepted Answer

Bacterial Meningitis

Answer

Viral Meningitis

Answer

Carcinomatous Meningitis

Answer

Acanthamoeba meningitis

Question 2

The following about leptospirosis is true except?

Accepted Answer

Tetracycline is the drug of choice

Answer

Seen in sewage workers

Answer

High fever with chills

Answer

Jaundice is present

Question 3

In tuberculous meningitis, what is NOT seen:

Accepted Answer

Increased CSF glucose

Answer

Turbidity of CSF

Answer

Increased lymphocytes

Answer

Decreased protein levels

Question 4

A 34-year-old lady presents with high grade fever with chills and rigors. On examination a firm spleen is felt 3 cm below costal margin with right upper quadrant tenderness. Peripheral smear was prepared. Diagnosis is?

Accepted Answer

Plasmodium falciparum

Answer

Infectious mononucleosis

Answer

Plasmodium vivax

Answer

Amoebic liver abscess

Question 5

A microbiology laboratory reports growth of Staphylococcus aureus from pus drained from a breast abscess. What is the most likely condition predisposing the patient to the development of a breast abscess?

Accepted Answer

Breast feeding

Answer

Endocarditis

Answer

Menopause

Answer

Inflammatory breast carcinoma

Question 6

In bacterial meningitis, CSF has:

Accepted Answer

High protein

Answer

High glucose

Answer

High neutrophils

Answer

High lymphocytes

Question 7

A 40-year-old man presents with fever, productive cough, shortness of breath, mild confusion, and diarrhea. Ten days earlier, he used a shower in a public facility. Sputum Gram stain and direct fluorescent antibody testing are performed, and chest imaging is shown. Which laboratory abnormality is most likely?

Accepted Answer

Hyponatremia

Answer

Hypercalcemia

Answer

Hypernatremia

Answer

Hypocalcemia

Question 8

Most common muscle involved in Tropical pyomyositis

Accepted Answer

Quadriceps

Answer

Triceps

Answer

Biceps

Answer

Gluteus

Question 9

Six days after receiving several flea bites in a rat-infested shed, a homeless 24-year-old man develops fever, chills, and a rash that spreads from his abdomen to cover his extremities. He is seen at the hospital emergency department, where blood is drawn for analysis. Eight days later, the public health department reports the presence of antibody to one of the rickettsial group antigens. Which of the following is the most likely diagnosis?

Accepted Answer

Endemic typhus

Answer

Epidemic typhus

Answer

Q fever

Answer

Rocky Mountain spotted fever

Question 10

Negative Mantoux test is when induration is:

Accepted Answer

<5mm

Answer

<15mm

Answer

<20mm

Answer

<10mm

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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