Infectious Diseases Practice Questions

Q: A long-term diabetic patient with blisters walked barefoot for a few miles on hot sand. He presented with rapidly spreading deep tissue infection with extensive tissue necrosis. What is the most probable diagnosis?

Necrotizing fasciitis. ***Necrotizing fasciitis*** - The rapid spread of deep tissue infection with extensive necrosis, especially in an immunocompromised patient like a diabetic, is highly characteristic of **necrotizing fasciitis**. [1] - **Diabetic peripheral neuropathy** can lead to unnoticed injury (walking barefoot on hot sand) and impaired wound healing, further predisposing to severe infections. [2] *Burn* - While walking on hot sand can cause burns, this patient's presentation of "rapidly spreading deep tissue infection" and "extensive tissue necrosis" goes beyond a typical burn injury, suggesting an overwhelming infection. - Burns primarily involve direct tissue damage from heat, whereas the described pathology is indicative of a **bacterial infection** escalating rapidly. *Cellulitis* - **Cellulitis** is a superficial skin infection that typically presents as localized redness, warmth, and swelling, but it usually does not involve deep tissue necrosis or such rapid, extensive spread. - It lacks the hallmark sign of rapid progression to **necrosis** and involvement of deep fascial planes that necessitate urgent surgical debridement. *Diabetic foot* - **Diabetic foot** is a broad term encompassing various foot complications in diabetes, including ulcers, infections, and Charcot arthropathy. While this patient has a diabetic foot, the specific presentation of **rapidly spreading infection** with **extensive necrosis** points to a particular, severe diagnosis within the diabetic foot spectrum, rather than the general term. [2] - The context describes a specific acute, life-threatening infectious process rather than the chronic complications typically associated with the general term "diabetic foot."

Q: A 40-year-old male presents with fever and abdominal pain and is diagnosed with HIV and TB. What is the most appropriate sequence of treatment?

ATT followed by ART within 2-8 weeks. ***ATT followed by ART within 2-8 weeks*** - This sequence is crucial for patients with co-infection of **HIV and TB**. Initiating **anti-tuberculous treatment (ATT)** first is vital to control the active TB infection, which can be rapidly fatal [2]. - Subsequently, starting **antiretroviral therapy (ART)** within 2-8 weeks (typically 2-4 weeks after ATT in patients without CNS TB) helps to restore the immune system and prevent other opportunistic infections, but delaying it slightly reduces the risk of **IRIS (Immune Reconstitution Inflammatory Syndrome)** [1]. *First ATT and then ART* - While starting ATT first is correct, this option is too vague regarding the timing of ART initiation. - The specific window of 2-8 weeks (or 2-4 weeks without CNS TB) is important to balance TB treatment efficacy and mitigate **IRIS risk** [1]. *ATT only* - This approach is incorrect as it fails to address the underlying HIV infection, which would lead to continued immune decline and increased morbidity and mortality. - ART is essential for improving prognosis and reducing viral load in HIV-infected individuals. *First ART and then ATT* - Initiating ART before ATT in co-infected patients with active TB can worsen the TB condition due to **IRIS**, which can be severe and life-threatening [1]. - ART can cause a rapid immune reconstitution and paradoxical worsening of symptoms or presentation of subclinical TB [1].

Q: MC cause of atypical pneumonia?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - *M. pneumoniae* is the most common cause of **atypical pneumonia**, often referred to as **"walking pneumonia"** due to milder symptoms compared to typical bacterial pneumonia. - It lacks a **cell wall**, making it resistant to many common antibiotics like penicillin and cephalosporins. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* typically causes **lobar pneumonia**, particularly in individuals with compromised immune systems or alcoholism. - It is associated with **severe symptoms**, such as thick, "currant jelly" sputum, and often forms dense consolidated infiltrates on chest X-rays. [1] *Hemophilus influenzae* - *Haemophilus influenzae* is a common cause of **bacterial pneumonia**, especially in children and adults with underlying lung disease (e.g., COPD). - It usually presents as **typical pneumonia** with more acute and severe symptoms, rather than the milder, atypical presentation. *Chlamydia* - While *Chlamydia pneumoniae* can cause a form of atypical pneumonia, it is **less common** than *Mycoplasma pneumoniae* as the primary cause. [1] - *Chlamydia* infections can also cause other conditions, such as **urethritis** and **cervicitis**, depending on the species involved.

Q: Chronic viral hepatitis is seen with all of the following viruses, except?

HEV. ***HEV*** - While HEV can cause acute hepatitis, it **rarely progresses to chronic infection** in immunocompetent individuals. - Chronic HEV infection is primarily seen in **immunocompromised patients**, such as organ transplant recipients. *HCV* - **Hepatitis C virus** is well-known for its high propensity to establish chronic infection, with about 75-85% of acutely infected individuals developing **chronic hepatitis** [1]. - Chronic HCV infection can lead to **cirrhosis**, liver failure, and hepatocellular carcinoma [1]. *HBV* - **Hepatitis B virus** is a major cause of chronic hepatitis worldwide, especially when acquired perinatally or in early childhood [1]. - Approximately 5-10% of immunocompetent adults who acquire acute HBV infection progress to **chronic hepatitis** [1]. *HDV* - **Hepatitis D virus** is a defective virus that requires co-infection with HBV to replicate; therefore, chronic HDV infection only occurs in individuals with chronic HBV. - Co-infection or superinfection with HDV often **accelerates the progression of liver disease** to cirrhosis and liver failure.

Q: The following serological status is noted in a patient: HbsAg positive and HbeAg positive. Diagnosis is?

Active hepatitis B with high infectivity. ***Active hepatitis B with high infectivity*** - The presence of **HBsAg** indicates ongoing **hepatitis B infection** (either acute or chronic) [1]. - The presence of **HBeAg** signifies active **viral replication** and **high infectivity**, meaning the patient can easily transmit the virus [1]. *Chronic viral hepatitis* - While the patient does have hepatitis B, simply stating "chronic viral hepatitis" is less specific and doesn't fully capture the **infectivity status**. - **Chronic hepatitis B** is defined by **HBsAg persistence** for more than six months, but a high infectivity state is specifically implied by HBeAg positivity [1]. *Remote infection* - **Remote infection** would typically be indicated by the presence of **anti-HBs** and **anti-HBc IgG** antibodies, with no detectable HBsAg [1]. - The patient's **HBsAg positive** status rules out a remote infection where the virus has been cleared [1]. *Resolved hepatitis B infection* - A resolved hepatitis B infection is characterized by **loss of HBsAg** and the development of **anti-HBs antibodies**, indicating immunity [1]. - The patient's **HBsAg positive** status definitively indicates that the infection is not resolved and is still active [1].

Q: Tropical pulmonary eosinophilia is most characteristically seen due to which of the following infections?

Filaria. *Filaria* - **Tropical pulmonary eosinophilia (TPE)** is a hypersensitivity reaction to microfilariae from filarial nematodes like *Wuchereria bancrofti* and *Brugia malayi* [1]. - It is characterized by cough, dyspnea, wheezing, and marked **peripheral eosinophilia**, with interstitial infiltrates on chest X-ray [1]. *Roundworm* - **Ascaris lumbricoides** can cause **Loeffler's syndrome**, a transient pulmonary infiltration with eosinophilia during larval migration, but not chronic TPE [2]. - Symptoms are usually less severe and self-limiting compared to TPE [2]. *Trichinella* - **Trichinella spiralis** causes **trichinellosis**, presenting with muscle pain, fever, and periorbital edema, possibly with eosinophilia, but typically does not manifest as TPE. - Pulmonary involvement is rare and not the characteristic feature. *Ancylostoma* - **Hookworm (Ancylostoma duodenale, Necator americanus)** larvae can cause mild pulmonary symptoms and eosinophilia during migration through the lungs [3]. - However, they also do not typically lead to the severe and chronic pulmonary symptoms seen in TPE [3].

Q: Meningococcal meningitis is seen with which of the following complement deficiency?

C5. ***C5*** - Deficiencies in terminal complement components (C5-C9) lead to impaired formation of the **membrane attack complex (MAC)**, which is crucial for lysing Neisseria species [1]. - This significantly increases susceptibility to recurrent infections, particularly by **encapsulated bacteria** like *Neisseria meningitidis*, causing diseases such as meningococcal meningitis [2]. *C4* - C4 deficiency is primarily associated with **lupus-like syndromes** and **vasculitis**, due to impaired clearance of immune complexes. - While it can lead to some increased risk of infection, it is not specifically linked to a marked predisposition to meningococcal disease. *C1q* - C1q deficiency also leads to impaired **immune complex clearance** and is strongly associated with **systemic lupus erythematosus (SLE)**. - Like C4 deficiency, it does not typically present with recurrent meningococcal infections as the primary manifestation. *C2* - C2 deficiency is the **most common complement deficiency** and is associated with **lupus-like syndromes** and increased susceptibility to **pyogenic bacterial infections**. - Though it can lead to some increased infection risk, C2 deficiency is not as strongly or specifically linked to recurrent meningococcal meningitis as deficiencies in the terminal complement pathway [2].

Q: Hemolytic uraemic syndrome is associated with

E. coli 0157. ***E. coli O157*** - **Hemolytic uremic syndrome (HUS)** is most commonly associated with infection by **Shiga toxin-producing E. coli (STEC)**, particularly serotype O157:H7 [2]. - The Shiga toxin damages the **endothelium** of blood vessels, leading to **thrombotic microangiopathy**, which manifests as **hemolytic anemia**, **thrombocytopenia**, and **acute kidney injury** [1], [2]. *Bartonella henselae* - This bacterium is the causative agent of **cat scratch disease**, characterized by **lymphadenopathy** and sometimes systemic symptoms. - It is not typically associated with hemolytic uremic syndrome. *Malaria* - Malaria is a **parasitic infection** transmitted by mosquitoes, causing **fever**, **chills**, and **anemia** due to red blood cell lysis. - While it can cause anemia, it does not directly lead to the thrombotic microangiopathy of HUS. *Parvovirus B19* - **Parvovirus B19** causes **erythema infectiosum (fifth disease)** in children and can cause **aplastic crisis** in individuals with underlying hemolytic disorders. - It primarily targets erythroid precursors in the bone marrow but is not directly linked to HUS.

Q: Montenegro test is used for diagnosis of:

Kala azar. ***Kala azar*** - The Montenegro test, also known as the **leishmanin skin test (LST)**, detects delayed-type hypersensitivity to **Leishmania antigens**, indicating past or present infection with *Leishmania donovani*, the causative agent of **kala azar (visceral leishmaniasis)** [1]. - A **positive reaction** (induration of 5 mm or more) signifies cell-mediated immunity against the parasite [1]. *Leptospirosis* - Diagnosed primarily through **serological tests** like the **Microscopic Agglutination Test (MAT)** or by detecting the organism through **culture** or **PCR**. - The Montenegro test is not used for the diagnosis of **leptospirosis**. *Malaria* - Diagnosed by identifying **parasites in blood smears** (thick and thin films) or by **antigen detection rapid diagnostic tests (RDTs)**. - The Montenegro test plays no role in the diagnosis of **malaria**. *Leprosy* - Diagnosed through **clinical signs and symptoms**, microscopic examination of **skin or nerve biopsies for acid-fast bacilli**, or sometimes the **lepromin skin test**. - While the lepromin test is a skin test, it targets *Mycobacterium leprae* antigens and is distinct from the Montenegro test for leishmaniasis.

Question 1

A long-term diabetic patient with blisters walked barefoot for a few miles on hot sand. He presented with rapidly spreading deep tissue infection with extensive tissue necrosis. What is the most probable diagnosis?

Accepted Answer

Necrotizing fasciitis

Answer

Burn

Answer

Cellulitis

Answer

Diabetic foot

Question 2

A 40-year-old male presents with fever and abdominal pain and is diagnosed with HIV and TB. What is the most appropriate sequence of treatment?

Accepted Answer

ATT followed by ART within 2-8 weeks

Answer

First ATT and then ART

Answer

ATT only

Answer

First ART and then ATT

Question 3

MC cause of atypical pneumonia?

Accepted Answer

Mycoplasma pneumoniae

Answer

Klebsiella pneumoniae

Answer

Hemophilus influenzae

Answer

Chlamydia

Question 4

Chronic viral hepatitis is seen with all of the following viruses, except?

Accepted Answer

HEV

Answer

HCV

Answer

HBV

Answer

HDV

Question 5

The following serological status is noted in a patient: HbsAg positive and HbeAg positive. Diagnosis is?

Accepted Answer

Active hepatitis B with high infectivity

Answer

Chronic viral hepatitis

Answer

Remote infection

Answer

Resolved hepatitis B infection

Question 6

Tropical pulmonary eosinophilia is most characteristically seen due to which of the following infections?

Accepted Answer

Filaria

Answer

Roundworm

Answer

Trichinella

Answer

Ancylostoma

Question 7

Meningococcal meningitis is seen with which of the following complement deficiency?

Accepted Answer

C5

Answer

C4

Answer

C1q

Answer

C2

Question 8

Hemolytic uraemic syndrome is associated with

Accepted Answer

E. coli 0157

Answer

Bartonella henselae

Answer

Malaria

Answer

Parvovirus B19

Question 9

A 43-year-old woman has had a headache and fever for the past 2 weeks following a severe respiratory tract infection accompanying bronchiectasis. On physical examination, her temperature is 38.3degC. There is no papilledema. She has no loss of sensation or motor function, but there is decreased vision in the left half of her visual fields. CT scan of the head shows a sharply demarcated, 3-cm, a ring-enhancing lesion in the right occipital region. A lumbar puncture is done, and laboratory analysis of the CSF shows numerous leukocytes, increased protein, and normal glucose levels. What is the most likely diagnosis?

Accepted Answer

Localized brain infection with ring enhancement (e.g., cerebral abscess).

Answer

Demyelinating disease with white matter lesions (e.g., multiple sclerosis).

Answer

Primary brain tumor with ring enhancement (e.g., glioblastoma).

Answer

Secondary brain lesion from systemic malignancy (e.g., metastatic carcinoma).

Question 10

Montenegro test is used for diagnosis of:

Accepted Answer

Kala azar

Answer

Leptospirosis

Answer

Malaria

Answer

Leprosy

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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