Infectious Diseases Practice Questions

Q: A patient with HIV presents with a chronic cough and weight loss. A chest X-ray shows bilateral interstitial infiltrates. What is the most likely cause?

Pneumocystis jiroveci pneumonia. ***Pneumocystis jiroveci pneumonia*** - **Pneumocystis jiroveci pneumonia (PJP)** is a common opportunistic infection in HIV patients, presenting with **chronic cough**, **weight loss**, and **bilateral interstitial infiltrates** on chest X-ray [1]. - The insidious onset and classic radiographic findings are highly suggestive of PJP, especially in individuals with advanced HIV [1]. *Kaposi's sarcoma* - While common in HIV, **Kaposi's sarcoma** typically manifests as **cutaneous lesions**, though it can affect internal organs, including the lungs. - Lung involvement usually presents with **nodular** or **peribronchial infiltrates** and sometimes **pleural effusions**, which differ from the diffuse interstitial pattern described [1]. *Mycobacterium avium complex* - **Mycobacterium avium complex (MAC)** infection in HIV patients typically causes **disseminated disease** with fever, weight loss, and anemia [2]. - Pulmonary MAC often presents with **nodular** or **cavitary lesions** on imaging, not bilateral interstitial infiltrates. *Cryptococcal meningitis* - **Cryptococcal meningitis** is a central nervous system infection causing **headache**, **fever**, and **altered mental status**, not primarily respiratory symptoms [1]. - While *Cryptococcus* can cause pulmonary disease (**cryptococcosis**), it's less common to present with chronic cough and exclusively interstitial infiltrates compared to PJP.

Q: A patient from a Lyme disease-endemic area presents with erythema migrans, fatigue, and arthralgia. Laboratory tests show positive IgM antibodies against Borrelia burgdorferi. Evaluate the stage of Lyme disease.

Early localized. ***Early localized*** - **Erythema migrans** is the hallmark rash of early localized Lyme disease, typically appearing within days to weeks of a tick bite [1]. - The presence of **fatigue** and **arthralgia** are non-specific symptoms that can occur at any stage, but along with positive **IgM antibodies**, are consistent with early infection. *Early disseminated* - This stage involves multiple erythema migrans lesions, **cranial nerve palsies** (e.g., Bell's palsy), **meningitis**, or **cardiac involvement** like AV block, none of which are described. - While fatigue and arthralgia can persist, the specific presentation points to the earliest stage before systemic spread with major organ involvement. *Late disseminated* - Characterized by chronic **arthritis** (especially in large joints), **encephalopathy**, or **neuropathy**, which typically develop months to years after the initial infection. - The patient's current symptoms are not indicative of these severe, chronic manifestations. *Post-Lyme disease syndrome* - Refers to persistent symptoms such as fatigue, joint pain, and cognitive difficulties lasting for more than 6 months after successful treatment of Lyme disease. - This patient presents with active infection symptoms, not chronic residual symptoms after treatment.

Q: A 30-year-old man presents with jaundice, fever, and right upper quadrant pain. He reports returning from a trip to Africa two weeks ago. Blood tests reveal elevated liver enzymes and a positive test for hepatitis B surface antigen. What is the most likely mode of transmission?

Parenteral. ***Parenteral*** - The presence of **hepatitis B surface antigen** indicates a **hepatitis B virus infection**. **Hepatitis B** is primarily transmitted through **parenteral routes**, including exposure to infected blood, sexual contact, or perinatal transmission [1]. - The recent travel to Africa, where hepatitis B is endemic, further supports this diagnosis, as exposure to contaminated needles or unsafe medical practices could have occurred via the **parenteral route**. *Fecal-oral* - **Fecal-oral transmission** is characteristic of **hepatitis A** and **hepatitis E**, typically contracted through contaminated food or water [1]. - The clinical presentation and positive hepatitis B surface antigen are inconsistent with **fecal-oral transmitted hepatitis**. *Respiratory droplets* - **Respiratory droplet transmission** is common for viruses like **influenza** or **measles** and is not a known mode of transmission for **hepatitis B**. - **Hepatitis B** does not spread through casual contact or breathing in infected droplets. *Vector-borne* - **Vector-borne transmission** involves an arthropod vector, such as mosquitoes or ticks, carrying the pathogen (e.g., malaria, dengue). - **Hepatitis B** is not transmitted via insect bites, making this mode of transmission unlikely.

Q: What is the initial step in the management of a patient with suspected meningitis following neurosurgery?

Administer empirical antibiotics. Administer empirical antibiotics - In suspected post-neurosurgical meningitis, empirical antibiotics should be initiated promptly to cover likely pathogens, given the high morbidity and mortality associated with delayed treatment [1]. - Delaying antibiotics for diagnostic procedures can worsen outcomes, especially if the patient's condition is deteriorating [1]. *Conduct a lumbar puncture* - While a lumbar puncture (LP) is crucial for definitive diagnosis, it should typically be performed *after* empirical antibiotics have been started, especially if there's a risk of intracranial pressure or focal neurological deficits. - An LP may be contraindicated or need careful consideration until imaging rules out mass effect, but delaying antibiotics for LP alone is generally not recommended in this critical situation. *Perform a CT scan of the head* - A CT scan is important to rule out mass lesions, hydrocephalus, or other surgical complications *prior* to a lumbar puncture, especially in neurosurgical patients. - However, performing a CT scan should not delay the administration of empirical antibiotics, which is the immediate priority in suspected meningitis. *Monitor neurological status* - Monitoring neurological status is an ongoing and essential part of managing any neurosurgical patient, including those with suspected meningitis. - However, mere monitoring is not an *initial step* in intervention; rather, it informs the urgency and effectiveness of active treatments like antibiotic administration.

Q: A patient with chronic hepatitis B is being evaluated for antiviral therapy. Recent lab results show high HBV DNA levels and normal ALT levels. What is the most appropriate next step in management?

Consider starting antiviral therapy immediately. Consider starting antiviral therapy immediately - **High HBV DNA levels** in a patient with chronic hepatitis B, even with normal ALT, indicate an **active viral replication** phase [1]. - This scenario often represents **HBeAg-positive (immune tolerant) phase** or early **HBeAg-negative (immune active) disease**, where treatment is often warranted to prevent progression to cirrhosis and hepatocellular carcinoma [1]. *Monitor liver function tests closely before deciding* - While monitoring ALT is important, **high HBV DNA levels** indicate ongoing viral activity and potential for liver damage, even if current ALT is normal [1]. - Delaying therapy based solely on normal ALT could miss an opportunity to prevent **long-term complications**. *Switch to a different antiviral agent if necessary* - This option is relevant for patients already on therapy who are experiencing **treatment failure** or resistance, which is not indicated here as the patient is being evaluated for *initiation* of therapy. - There is no mention of prior antiviral treatment, so switching agents is not applicable. *Perform a liver biopsy to assess fibrosis* - A liver biopsy can provide information about the degree of inflammation and fibrosis, but it is an **invasive procedure** and often reserved for cases where the decision to treat is not clear-cut based on non-invasive markers. - In cases of high viral load, treatment is often initiated regardless of biopsy findings, and **non-invasive tests** (e.g., FibroScan) are increasingly preferred for fibrosis assessment.

Q: A patient presents with diarrhea following a course of broad-spectrum antibiotics. Stool tests positive for toxin B DNA. What is the best management approach?

Initiate oral vancomycin treatment. ***Initiate oral vancomycin treatment*** - The patient's symptoms (diarrhea post-antibiotics) and positive **toxin B DNA** indicate **Clostridioides difficile infection (CDI)** [1]. - **Oral vancomycin** is a first-line treatment for CDI due to its bioavailability in the GI tract, effectively targeting the bacteria [2]. *Continue current antibiotics* - Continuing the **broad-spectrum antibiotics** would likely exacerbate the CDI by further disrupting the normal gut flora [3]. - The current antibiotics are the probable cause of the initial **gut dysbiosis** allowing *C. difficile* to proliferate [1]. *Switch to a different antibiotic* - Switching to another broad-spectrum antibiotic is unlikely to treat CDI effectively and may even worsen the condition. - CDI requires specific treatment with agents like **vancomycin** or **fidaxomicin** that target *C. difficile* [2]. *Recommend probiotics only* - While probiotics can sometimes help restore normal gut flora, they are **insufficient as a sole treatment** for established CDI. - Probiotics do not directly eradicate *C. difficile* and are not a substitute for targeted antibiotic therapy in symptomatic infection.

Q: A 25-year-old man presents with non-anesthetic hypopigmented macules on his arm and has a family history of leprosy. What is the most appropriate diagnostic test?

Skin biopsy. ***Skin biopsy*** - A **skin biopsy** of the affected lesion, particularly the edge, is the most appropriate diagnostic test to confirm leprosy by identifying **acid-fast bacilli (AFB)** or characteristic histological changes like granulomas and nerve involvement. - It allows for the differentiation of leprosy from other hypopigmenting conditions and classification into specific types based on the **Ridley-Jopling classification**. *KOH mount* - A **KOH mount** is primarily used to diagnose **fungal infections** by dissolving keratinocytes and allowing visualization of fungal elements. - It would not be useful for identifying the acid-fast bacilli of *Mycobacterium leprae* or for assessing nerve involvement. *PCR for Mycobacterium leprae* - While **PCR is highly sensitive** for detecting *M. leprae* DNA, it is not the **first-line diagnostic test** and is usually reserved for cases where conventional methods are inconclusive or for research purposes. - It may not always correlate with disease activity or viability of the bacilli, and false positives can occur. *Slit skin smear* - A **slit skin smear** is used to determine the **bacterial index (BI)** and **morphological index (MI)** in leprosy, particularly in patients with multiple lesions or suspected lepromatous leprosy [1]. - However, in cases of **paucibacillary leprosy** (tuberculoid type), the smear may be negative, making a biopsy more reliable for diagnosis and classification, especially with **non-anesthetic hypopigmented macules** [1].

Q: A patient with AIDS presents with fever and weight loss. A biopsy of a lymph node shows intracellular amastigotes. Which organism is likely responsible?

Leishmania donovani (causes visceral leishmaniasis). ***Leishmania donovani (causes visceral leishmaniasis)*** - The presence of **intracellular amastigotes** in a lymph node biopsy, combined with fever and weight loss in an **AIDS patient**, is highly suggestive of **visceral leishmaniasis** caused by *Leishmania donovani* [1]. - **Immunocompromized individuals**, particularly those with AIDS, are highly susceptible to severe and disseminated forms of leishmaniasis, leading to **visceral involvement** [1]. *Trypanosoma cruzi (causes Chagas disease)* - While *Trypanosoma cruzi* is an intracellular parasite and can be found in tissue, its amastigotes are typically found within **cardiac and smooth muscle cells**, not primarily in lymph nodes. - **Chagas disease** primarily affects the heart and gastrointestinal tract, and while amastigotes are seen, the overall clinical context and preferred tissue for biopsy differ. *Plasmodium falciparum (causes malaria)* - *Plasmodium falciparum* are **intracellular parasites** that infect **red blood cells**, not lymph nodes. - The classic presentation of malaria involves **cyclic fevers**, chills, and anemia, and the diagnosis is made by identifying parasites in **blood smears**. *Toxoplasma gondii (opportunistic infection)* - *Toxoplasma gondii* can cause disseminated disease in **AIDS patients**, particularly **encephalitis**, and forms **cysts** (bradyzoites) in various tissues including the brain, muscle, and lymph nodes. - However, the characteristic finding in *Toxoplasma* infection is usually **cysts** or **tachyzoites** in tissue, not the distinct amastigote form seen in Leishmania, and lymph node involvement is often as a toxoplasmic lymphadenitis rather than disseminated amastigotes.

Q: A 45-year-old woman presents with jaundice and elevated liver enzymes. A serological test is positive for HBsAg and anti-HBc IgM. What is the stage of her hepatitis B infection?

Acute. ***Acute*** - The presence of **HBsAg** (hepatitis B surface antigen) indicates active infection, while **anti-HBc IgM** (antibody to hepatitis B core antigen, IgM class) specifically points to a recent, **acute infection** [1]. - Elevated liver enzymes and jaundice further support a recent, **active inflammatory process** in the liver. *Chronic* - Chronic hepatitis B is characterized by the presence of **HBsAg for more than 6 months**, often with **anti-HBc IgG** rather than IgM [1]. - The presence of **anti-HBc IgM** rules out a purely chronic infection, as it signifies recent exposure. *Resolved* - A resolved infection typically shows **negative HBsAg** and **positive anti-HBs** (antibody to hepatitis B surface antigen), indicating immunity [1]. - The presence of **HBsAg** means the infection is still active, not resolved. *Carrier* - The term "carrier" refers to a person with chronic hepatitis B infection (HBsAg positive for >6 months), often with relatively stable liver enzymes and minimal liver damage, but can also refer to chronic active hepatitis. - The presence of **anti-HBc IgM** indicates an **acute phase**, not a stable carrier state without acute viral replication.

Question 1

A patient with HIV presents with a chronic cough and weight loss. A chest X-ray shows bilateral interstitial infiltrates. What is the most likely cause?

Accepted Answer

Pneumocystis jiroveci pneumonia

Answer

Kaposi's sarcoma

Answer

Mycobacterium avium complex

Answer

Cryptococcal meningitis

Question 2

A 35-year-old man presents with an eschar following a recent hike in a scrub typhus-endemic area. Despite initial doxycycline therapy, the patient remains febrile after 48 hours. What is the most appropriate next step?

Accepted Answer

Evaluate for antibiotic resistance and consider alternative antibiotics

Answer

Increase the doxycycline dose

Answer

Switch to a third-generation cephalosporin

Answer

Add azithromycin to the treatment regimen

Question 3

A patient from a Lyme disease-endemic area presents with erythema migrans, fatigue, and arthralgia. Laboratory tests show positive IgM antibodies against Borrelia burgdorferi. Evaluate the stage of Lyme disease.

Accepted Answer

Early localized

Answer

Early disseminated

Answer

Late disseminated

Answer

Post-Lyme disease syndrome

Question 4

A 30-year-old man presents with jaundice, fever, and right upper quadrant pain. He reports returning from a trip to Africa two weeks ago. Blood tests reveal elevated liver enzymes and a positive test for hepatitis B surface antigen. What is the most likely mode of transmission?

Accepted Answer

Parenteral

Answer

Fecal-oral

Answer

Respiratory droplets

Answer

Vector-borne

Question 5

What is the initial step in the management of a patient with suspected meningitis following neurosurgery?

Accepted Answer

Administer empirical antibiotics

Answer

Conduct a lumbar puncture

Answer

Perform a CT scan of the head

Answer

Monitor neurological status

Question 6

A patient with chronic hepatitis B is being evaluated for antiviral therapy. Recent lab results show high HBV DNA levels and normal ALT levels. What is the most appropriate next step in management?

Accepted Answer

Consider starting antiviral therapy immediately

Answer

Monitor liver function tests closely before deciding

Answer

Switch to a different antiviral agent if necessary

Answer

Perform a liver biopsy to assess fibrosis

Question 7

A patient presents with diarrhea following a course of broad-spectrum antibiotics. Stool tests positive for toxin B DNA. What is the best management approach?

Accepted Answer

Initiate oral vancomycin treatment

Answer

Continue current antibiotics

Answer

Switch to a different antibiotic

Answer

Recommend probiotics only

Question 8

A 25-year-old man presents with non-anesthetic hypopigmented macules on his arm and has a family history of leprosy. What is the most appropriate diagnostic test?

Accepted Answer

Skin biopsy

Answer

KOH mount

Answer

PCR for Mycobacterium leprae

Answer

Slit skin smear

Question 9

A patient with AIDS presents with fever and weight loss. A biopsy of a lymph node shows intracellular amastigotes. Which organism is likely responsible?

Accepted Answer

Leishmania donovani (causes visceral leishmaniasis)

Answer

Trypanosoma cruzi (causes Chagas disease)

Answer

Plasmodium falciparum (causes malaria)

Answer

Toxoplasma gondii (opportunistic infection)

Question 10

A 45-year-old woman presents with jaundice and elevated liver enzymes. A serological test is positive for HBsAg and anti-HBc IgM. What is the stage of her hepatitis B infection?

Accepted Answer

Acute

Answer

Chronic

Answer

Resolved

Answer

Carrier

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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