Clinical presentations of dimorphic fungal infections US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Clinical presentations of dimorphic fungal infections. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Clinical presentations of dimorphic fungal infections US Medical PG Question 1: An investigator is studying growth patterns of various fungal pathogens. Incubation of an isolated fungus at 25°C shows branching hyphae with rosettes of conidia under light microscopy. After incubation at 37°C, microscopic examination of the same organism instead shows smooth, white colonies with rounded, elongated cells. Infection with the investigated pathogen is most likely to cause which of the following conditions?
- A. Pityriasis versicolor
- B. Candidiasis
- C. Cryptococcosis
- D. Sporotrichosis (Correct Answer)
- E. Coccidioidomycosis
Clinical presentations of dimorphic fungal infections Explanation: ***Sporotrichosis***
- The description of a fungal pathogen exhibiting **thermal dimorphism** (different forms at 25°C and 37°C) is characteristic of **Sporothrix schenckii**.
- At 25°C, it typically grows as **mold with branching hyphae and conidia in rosettes**, and at 37°C, it grows as **yeast-like cells (cigar-shaped bodies in tissue)**, which can appear rounded and elongated.
*Pityriasis versicolor*
- Caused by **Malassezia globosa**, which is a **lipophilic yeast** and does not exhibit thermal dimorphism described here.
- Characterized by **hypo- or hyperpigmented skin patches**, not deep tissue infection with dimorphic growth.
*Candidiasis*
- Caused by **Candida species**, which are **opportunistic yeasts** that can form pseudohyphae and true hyphae but do not display the specific dimorphism with rosettes of conidia at 25°C.
- Infections range from superficial mucocutaneous to systemic, but the fungal morphology described does not fit.
*Cryptococcosis*
- Caused by **Cryptococcus neoformans** or **Cryptococcus gattii**, which are **encapsulated yeasts** and do not exhibit dimorphism (mold at 25°C, yeast at 37°C).
- Primarily causes **meningoencephalitis** or pulmonary disease, and is identified by its capsule and yeast form.
*Coccidioidomycosis*
- Caused by **Coccidioides immitis** or **Coccidioides posadasii**, which are **thermally dimorphic fungi**, but their morphology differs from the description.
- At 25°C, they grow as molds with **arthroconidia**, and at 37°C, they form **spherules containing endospores** in tissue, not smooth, white colonies with rounded, elongated cells.
Clinical presentations of dimorphic fungal infections US Medical PG Question 2: A 47-year-old woman comes to the physician because of a 3-day history of fever, fatigue, loss of appetite, cough, and chest pain. Physical examination shows diffuse inspiratory crackles over the left lung field. An x-ray of the chest shows hilar lymphadenopathy and well-defined nodules with central calcifications. Urine studies show the presence of a polysaccharide antigen. A biopsy specimen of the lung shows cells with basophilic, crescent-shaped nuclei and pericellular halos located within macrophages. This patient's history is most likely to show which of the following?
- A. Visit to Arizona desert
- B. Recent trip to Brazil
- C. Previous mycobacterial infection
- D. Exposure to bat droppings (Correct Answer)
- E. Treatment with inhaled glucocorticoids
Clinical presentations of dimorphic fungal infections Explanation: ***Exposure to bat droppings***
- The clinical presentation, including fever, cough, chest pain, **hilar lymphadenopathy**, **nodules with central calcifications**, and **intracellular encapsulated yeasts** in macrophages, is classic for **histoplasmosis**.
- **Histoplasma capsulatum** is endemic to the Ohio and Mississippi River valleys and is transmitted through inhalation of spores from soil contaminated with **bat or bird droppings**.
*Visit to Arizona desert*
- Exposure in the **Arizona desert** is associated with **coccidioidomycosis** (Valley Fever), which presents with similar pulmonary symptoms but is caused by Coccidioides immitis/posadasii, characterized by **spherules** containing endospores.
- While it can cause hilar lymphadenopathy and nodules, the characteristic intracellular budding yeasts within macrophages and the polysaccharide antigen in urine point away from coccidioidomycosis.
*Recent trip to Brazil*
- A trip to **Brazil** might suggest diseases like **Paracoccidioidomycosis**, which presents with chronic mucocutaneous or disseminated lesions, or various tropical infections, but is not typically characterized by the specific pulmonary and microscopic findings described here.
- The histopathological findings of **intracellular yeasts with pericellular halos** (consistent with Histoplasma) would not be the primary finding for paracoccidioidomycosis, which generally shows characteristic **"pilot wheel"** or multiple budding yeasts.
*Previous mycobacterial infection*
- A previous **mycobacterial infection** would lead to tuberculosis, characterized by **acid-fast bacilli** and granulomas with **caseating necrosis**, which is different from the described intracellular yeasts and polysaccharide antigen.
- While tuberculosis can cause hilar lymphadenopathy and pulmonary nodules, the given microscopic description of cells with basophilic nuclei and pericellular halos within macrophages does not fit Mycobacterium tuberculosis.
*Treatment with inhaled glucocorticoids*
- Inhaled glucocorticoids are used to treat conditions like asthma or COPD and, while prolonged use can rarely predispose to **opportunistic fungal infections** (e.g., aspergillosis, candidiasis), they are not a cause of this specific clinical presentation or the microbiological findings of histoplasmosis.
- The use of inhaled steroids would not explain the geographic exposure, hilar lymphadenopathy, or the specific appearance of the fungal elements within macrophages described.
Clinical presentations of dimorphic fungal infections US Medical PG Question 3: A 40-year-old farmer from Ohio seeks evaluation at a clinic with complaints of a chronic cough, fevers, and anorexia of several months duration. On examination, he has generalized lymphadenopathy with hepatosplenomegaly. A chest radiograph reveals local infiltrates and patchy opacities involving all lung fields. Fine needle aspiration of an enlarged lymph node shows the presence of intracellular yeast. A fungal culture shows the presence of smooth, thin-walled microconidia and tuberculate macroconidia. Which of the following is the most likely diagnosis?
- A. Coccidioidomycosis
- B. Blastomycosis
- C. Cryptococcosis
- D. Histoplasmosis (Correct Answer)
- E. Sporotrichosis
Clinical presentations of dimorphic fungal infections Explanation: ***Histoplasmosis***
- **Histoplasmosis** is characterized by the presence of **intracellular yeast** in tissue samples and **tuberculate macroconidia** in fungal cultures, which are key diagnostic findings in this case.
- The patient's presentation with chronic cough, fevers, anorexia, generalized lymphadenopathy, hepatosplenomegaly, and lung infiltrates, along with geographic exposure in **Ohio** (part of the Ohio River Valley endemic area), is highly consistent with disseminated histoplasmosis.
*Coccidioidomycosis*
- While coccidioidomycosis can cause lung infiltrates, it is typically endemic to the **southwestern United States** and Mexico, not Ohio.
- Microscopic examination would reveal **spherules** containing endospores, not intracellular yeast with tuberculate macroconidia.
*Blastomycosis*
- Blastomycosis is also endemic to the Ohio River Valley, but it is characterized by **broad-based budding yeast** in tissue, and its cultures typically do not show tuberculate macroconidia.
- While it causes pulmonary and disseminated disease, the specific microscopic and culture findings differentiate it from histoplasmosis.
*Cryptococcosis*
- Cryptococcosis primarily affects immunocompromised individuals and is characterized by encapsulated yeast, which would be visible with India ink stain.
- It typically presents as **meningitis** or pneumonia, and its culture morphology does not include tuberculate macroconidia.
*Sporotrichosis*
- Sporotrichosis is commonly associated with **cutaneous lesions** following traumatic inoculation of spores from soil or vegetation, and it rarely causes disseminated disease with extensive systemic symptoms like those described.
- The yeast forms in tissue are typically smaller and cigar-shaped, and the culture morphology differs significantly from what is described.
Clinical presentations of dimorphic fungal infections US Medical PG Question 4: A 58-year-old man presents with a high-grade fever, throbbing left-sided headache, vision loss, and left orbital pain. He says that his symptoms started acutely 2 days ago with painful left-sided mid-facial swelling and a rash, which progressively worsened. Today, he woke up with complete vision loss in his left eye. His past medical history is significant for type 2 diabetes mellitus, diagnosed 5 years ago. He was started on an oral hypoglycemic agent which he discontinued after a year. His temperature is 38.9°C (102.0°F), blood pressure is 120/80 mm Hg, pulse is 120/min, and respiratory rate is 20/min. On examination, there is purulent discharge from the left eye and swelling of the left half of his face including the orbit. Oral examination reveals extensive necrosis of the palate with a black necrotic eschar and purulent discharge. Ophthalmic examination is significant for left-sided ptosis, proptosis, and an absence of the pupillary light reflex. Laboratory findings are significant for a blood glucose level of 388 mg/dL and a white blood cell count of 19,000 cells/mm³. Urinary ketone bodies are positive. Fungal elements are found on a KOH mount of the discharge. Which of the following statements best describes the organism responsible for this patient’s condition?
- A. It appears as a narrow-based budding yeast with a thick capsule
- B. Histopathological examination shows non-septate branching hyphae (Correct Answer)
- C. It produces conidiospores
- D. It has budding and filamentous forms
- E. Histopathological examination shows acute angle branching hyphae
Clinical presentations of dimorphic fungal infections Explanation: ***Histopathological examination shows non-septate branching hyphae***
- The patient's presentation with **diabetic ketoacidosis**, orbital pain, vision loss, facial swelling, necrotic palatal eschar, and high fever strongly suggests **mucormycosis**, a severe fungal infection.
- Mucormycosis is caused by fungi belonging to **Mucorales order** (e.g., *Rhizopus*, *Mucor*, *Lichtheimia*), which are characterized by **broad, ribbon-like, non-septate hyphae with irregular, wide-angle branching**.
*It appears as a narrow-based budding yeast with a thick capsule*
- This description is characteristic of **Cryptococcus neoformans**, which causes cryptococcosis, often presenting with meningoencephalitis and lung involvement.
- The clinical picture and *KOH mount* findings in this patient are inconsistent with cryptococcosis.
*It produces conidiospores*
- **Conidiospores are asexual spores** produced by many fungi, including *Aspergillus* and *Penicillium*, but this is a general characteristic and not specific enough to definitively identify the pathogen responsible for mucormycosis.
- The *histopathological features* (non-septate hyphae) are the key identifier in mucormycosis.
*It has budding and filamentous forms*
- This description generally refers to **dimorphic fungi** (e.g., *Histoplasma*, *Blastomyces*, *Coccidioides*), which exhibit yeast forms in tissue and mold forms in culture.
- Mucorales are typically **molds** in both environments and are not considered dimorphic, nor do they commonly present with budding forms.
*Histopathological examination shows acute angle branching hyphae*
- This morphological description is characteristic of **Aspergillus species**, which cause aspergillosis, another opportunistic fungal infection.
- *Aspergillus* hyphae are typically **septate** and branch at acute angles (around 45 degrees), unlike the broad, non-septate, wide-angle branching hyphae of Mucorales.
Clinical presentations of dimorphic fungal infections US Medical PG Question 5: A 29-year-old woman comes to the military physician because of a 2-day history of fever, joint pain, dry cough, chest pain, and a painful red rash on her lower legs. Two weeks ago, she returned from military training in Southern California. She appears ill. Her temperature is 39°C (102.1°F). Physical examination shows diffuse inspiratory crackles over all lung fields and multiple tender erythematous nodules over the anterior aspect of both legs. A biopsy specimen of this patient's lungs is most likely to show which of the following?
- A. Septate hyphae with acute-angle branching
- B. Spherules filled with endospores (Correct Answer)
- C. Broad-based budding yeast
- D. Encapsulated yeast with narrow-based budding
- E. Oval, budding yeast with pseudohyphae
Clinical presentations of dimorphic fungal infections Explanation: **Spherules filled with endospores**
- The patient's symptoms (fever, joint pain, dry cough, chest pain, erythema nodosum on legs) combined with her travel history to **Southern California** are highly suggestive of **Coccidioidomycosis** ("Valley Fever").
- A biopsy of affected lung tissue in coccidioidomycosis typically reveals **spherules** (thick-walled structures) containing numerous **endospores**, which are characteristic of the tissue phase of *Coccidioides immitis/posadasii*.
*Septate hyphae with acute-angle branching*
- This morphology is characteristic of **Aspergillus** species, which can cause opportunistic infections, especially in immunocompromised individuals.
- While it can cause lung infections, the clinical presentation and geographic exposure do not point towards aspergillosis as the most likely diagnosis.
*Broad-based budding yeast*
- This describes the characteristic morphology of *Blastomyces dermatitidis*, the causative agent of **Blastomycosis**.
- **Blastomycosis** is typically found in the Great Lakes region, Ohio, Mississippi River valleys, and southeastern United States, not Southern California.
*Encapsulated yeast with narrow-based budding*
- This describes **Cryptococcus neoformans**, which appears as an encapsulated yeast with narrow-based budding in tissue.
- While it can cause pulmonary disease, the classic presentation (erythema nodosum, acute illness after Southern California exposure) is not consistent with **cryptococcosis**, which typically presents subacutely in immunocompromised patients.
*Oval, budding yeast with pseudohyphae*
- This morphology is characteristic of *Candida albicans*, which commonly causes mucocutaneous infections and can cause systemic candidiasis, particularly in immunocompromised patients.
- The clinical picture of a healthy young woman with exposure in Southern California does not fit with a typical **Candida** infection.
Clinical presentations of dimorphic fungal infections US Medical PG Question 6: A 3-month-old girl is brought to the emergency department because of a 2-day history of progressive difficulty breathing and a dry cough. Five weeks ago, she was diagnosed with diffuse hemangiomas involving the intrathoracic cavity and started treatment with prednisolone. She appears uncomfortable and in moderate respiratory distress. Her temperature is 38°C (100.4°F), pulse is 150/min, respirations are 50/min, and blood pressure is 88/50 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 87%. Oral examination shows a white plaque covering the tongue that bleeds when scraped. Chest examination shows subcostal and intercostal retractions. Scattered fine crackles and rhonchi are heard throughout both lung fields. Laboratory studies show a leukocyte count of 21,000/mm3 and an increased serum beta-D-glucan concentration. An x-ray of the chest shows symmetrical, diffuse interstitial infiltrates. Which of the following is most likely to confirm the diagnosis?
- A. Tuberculin skin test
- B. Urine antigen test
- C. CT scan of the chest
- D. Bronchoalveolar lavage (Correct Answer)
- E. DNA test for CFTR mutation
Clinical presentations of dimorphic fungal infections Explanation: ***Bronchoalveolar lavage***
- The patient, an infant on **prednisolone** (immunosuppression) with **diffuse interstitial infiltrates**, **uncomfortable appearance**, **respiratory distress**, and **oral thrush (white plaque that bleeds when scraped)**, points to **Pneumocystis pneumonia (PCP)**.
- **Bronchoalveolar lavage (BAL)** is the gold standard for diagnosing PCP by identifying **Pneumocystis jirovecii cysts** or **trophozoites** using special stains (e.g., Giemsa, methenamine silver).
*Tuberculin skin test*
- The **tuberculin skin test** is used to diagnose **tuberculosis**, which typically presents with **granulomas** and **cavitary lesions** on chest X-ray, not diffuse interstitial infiltrates.
- While tuberculosis can cause respiratory symptoms, the presence of oral thrush and immunosuppression suggests an opportunistic fungal infection like PCP rather than TB.
*Urine antigen test*
- A **urine antigen test** is commonly used for diagnosing **Legionnaires' disease** or **pneumococcal pneumonia** in adults, and is not applicable for PCP.
- It does not detect *Pneumocystis jirovecii*, which is the suspected pathogen in this immunosuppressed infant.
*CT scan of the chest*
- A **CT scan of the chest** would show **diffuse ground-glass opacities** characteristic of PCP but is a **radiological finding**, not a definitive diagnostic test for the pathogen itself.
- While it can further characterize the pulmonary findings, it cannot identify the causative organism, which is crucial for targeted treatment.
*DNA test for CFTR mutation*
- A **DNA test for CFTR mutation** is used to diagnose **cystic fibrosis**, a genetic disorder affecting mucus production, and is not relevant in this acute presentation of respiratory distress and immunosuppression.
- Cystic fibrosis typically presents with recurrent respiratory infections, pancreatic insufficiency, and failure to thrive, not primarily with opportunistic infections like PCP.
Clinical presentations of dimorphic fungal infections US Medical PG Question 7: A 30-year-old man is admitted to the hospital with a presumed pneumonia and started on antibiotics. Two days later, the patient shows no improvement. Blood cultures reveal yeast with pseudophyphae. Which of the following cell types is most likely deficient or dysfunctional in this patient?
- A. Eosinophils
- B. Macrophages
- C. Neutrophils (Correct Answer)
- D. T-cells
- E. B-cells
Clinical presentations of dimorphic fungal infections Explanation: ***Neutrophils***
- The presence of **yeast with pseudohyphae** in blood cultures, particularly *Candida*, indicates a fungal infection.
- **Neutrophils** are crucial for the host defense against *Candida* and other fungal pathogens, so their deficiency or dysfunction would predispose to candidemia.
- Neutropenia or neutrophil dysfunction (e.g., chronic granulomatous disease) significantly increases risk of invasive candidiasis.
*Eosinophils*
- **Eosinophils** are primarily involved in defense against **parasitic infections** and in allergic reactions.
- They play a minimal role in the immune response to systemic fungal infections like candidemia.
*Macrophages*
- **Macrophages** are phagocytic cells that contribute to antifungal immunity, particularly in tissue surveillance and chronic infection control.
- However, **neutrophils** are the primary and most critical defense against acute *Candida* bloodstream infections.
- Macrophage deficiency alone does not typically predispose to candidemia as severely as neutrophil deficiency.
*T-cells*
- **T-cells** are important for cell-mediated immunity, particularly against **intracellular pathogens** and viral infections.
- While they play a role in modulating antifungal responses, their deficiency typically leads to infections with *Pneumocystis jirovecii* or severe mucocutaneous candidiasis, rather than disseminated candidemia.
*B-cells*
- **B-cells** are responsible for **humoral immunity** through antibody production, which is primarily effective against extracellular bacteria and toxins.
- They are not the primary line of defense against fungal infections such as candidemia.
Clinical presentations of dimorphic fungal infections US Medical PG Question 8: A 10-year-old girl is brought to the physician because of a severe, throbbing headache for 1 hour. The headache is located in the right frontotemporal region. It is her fifth such headache in the past 2 months. Her mother says that all the previous episodes started after soccer practice, following which the child would lock herself in her room, close the curtains, and sleep for a few hours. After waking up, the headache is either diminished or has stopped entirely. One month ago, the child was diagnosed with myopic vision and has been wearing glasses since. Her 4-year-old brother had herpetic gingivostomatitis 2 months ago. Her vital signs are within normal limits. Funduscopic examination is inconclusive because the child is uncooperative. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?
- A. MRI of the brain
- B. Acyclovir therapy
- C. Dihydroergotamine therapy
- D. Neuro-optometric assessment
- E. Acetaminophen therapy (Correct Answer)
Clinical presentations of dimorphic fungal infections Explanation: ***Acetaminophen therapy***
- This patient presents with symptoms highly suggestive of **migraine**, including a throbbing, unilateral headache, photophobia (wanting to close curtains), and improvement with sleep. **Acetaminophen** or NSAIDs are recommended as first-line abortive therapy for mild to moderate migraine attacks in children.
- Given the classic presentation and absence of **red-flag symptoms** (e.g., focal neurological deficits, altered mental status, papilledema), conservative management with an analgesic is the most appropriate initial step.
*MRI of the brain*
- An MRI is generally not indicated as the initial step for typical migraine presentations, especially when there are no **neurological deficits** or atypical features.
- While it can rule out structural abnormalities, the clinical picture strongly points towards a primary headache disorder, making imaging unnecessary at this stage.
*Acyclovir therapy*
- **Acyclovir** is an antiviral medication used to treat herpes virus infections. There is no indication of active herpes simplex virus (HSV) infection causing her headaches.
- The brother's **herpetic gingivostomatitis** 2 months prior is likely an unrelated past event and does not warrant antiviral therapy for the patient's current symptoms.
*Dihydroergotamine therapy*
- **Dihydroergotamine** is a potent vasoconstrictor used for acute migraine treatment, typically for severe attacks refractory to simpler analgesics. It is usually reserved for older adolescents and adults due to potential side effects like nausea and vomiting.
- It is not considered a first-line treatment for migraine in a 10-year-old girl, especially given the likelihood that milder medications would be effective.
*Neuro-optometric assessment*
- The patient was recently prescribed glasses for **myopia**, and while vision problems can cause headaches (**eyestrain headaches**), the characteristics here (throbbing, unilateral, photophobia, improvement with sleep) are more consistent with migraine.
- A specialized neuro-optometric assessment is not indicated as the initial step, as the current episode aligns well with migraine, and her existing vision correction addresses simple refractive error.
Clinical presentations of dimorphic fungal infections US Medical PG Question 9: A 57-year-old woman with non-small cell lung cancer comes to the physician 4 weeks after her tumor was resected. She takes no medications. The physician starts her on a treatment regimen that includes vinblastine. This treatment puts the patient at highest risk for which of the following?
- A. Pulmonary embolism
- B. Invasive fungal infection (Correct Answer)
- C. Progressive multifocal leukoencephalopathy
- D. Pulmonary fibrosis
- E. Heart failure
Clinical presentations of dimorphic fungal infections Explanation: ***Invasive fungal infection***
- Vinblastine is an **antimitotic chemotherapy agent** that, like other chemotherapeutic agents, can cause **myelosuppression**.
- **Myelosuppression** (particularly **neutropenia**) severely compromises the immune system, making patients highly susceptible to **opportunistic infections**, including invasive fungal infections.
*Pulmonary embolism*
- While cancer itself is a risk factor for **venous thromboembolism**, including pulmonary embolism, vinblastine itself **does not directly increase the risk** more than other chemotherapy agents.
- The highest risk with vinblastine specifically relates to its impact on bone marrow.
*Progressive multifocal leukoencephalopathy*
- This is a rare, severe opportunistic infection of the brain caused by the **JC virus**, primarily seen in patients with **severe immunosuppression**, such as those with HIV/AIDS or on chronic immunosuppressive therapy (e.g., natalizumab).
- While chemotherapy can cause immunosuppression, PML is not the most common or highest specific risk directly associated with vinblastine or its immediate, acute side effects compared to myelosuppression and opportunistic infections.
*Pulmonary fibrosis*
- **Pulmonary fibrosis** is a known side effect of certain chemotherapeutic agents like **bleomycin** and **busulfan**, but it is **not a primary or common adverse effect of vinblastine**.
- The side effect profile of vinblastine primarily involves myelosuppression, neurotoxicity, and gastrointestinal effects.
*Heart failure*
- **Cardiotoxicity leading to heart failure** is a significant concern with certain chemotherapy drugs, particularly **anthracyclines** (e.g., doxorubicin) and some tyrosine kinase inhibitors.
- **Vinblastine is not typically associated with cardiotoxicity or heart failure** as a primary or high-risk adverse effect.
Clinical presentations of dimorphic fungal infections US Medical PG Question 10: A 3-month-old male is brought to the emergency room by his mother who reports that the child has a fever. The child was born at 39 weeks of gestation and is at the 15th and 10th percentiles for height and weight, respectively. The child has a history of eczema. Physical examination reveals an erythematous fluctuant mass on the patient's inner thigh. His temperature is 101.1°F (38.4°C), blood pressure is 125/70 mmHg, pulse is 120/min, and respirations are 22/min. The mass is drained and the child is started on broad-spectrum antibiotics until the culture returns. The physician also orders a flow cytometry reduction of dihydrorhodamine, which is found to be abnormal. This patient is at increased risk of infections with which of the following organisms?
- A. Giardia lamblia
- B. Streptococcus viridans
- C. Aspergillus fumigatus (Correct Answer)
- D. Enterococcus faecalis
- E. Streptococcus pyogenes
Clinical presentations of dimorphic fungal infections Explanation: ***Aspergillus fumigatus***
- The abnormal **dihydrorhodamine (DHR) flow cytometry** test indicates **chronic granulomatous disease (CGD)**, a defect in phagocyte function.
- Patients with CGD are particularly susceptible to **catalase-positive organisms**, including *Aspergillus* species, *Staphylococcus aureus*, *Serratia marcescens*, *Burkholderia cepacia*, and *Nocardia* species.
*Giardia lamblia*
- *Giardia lamblia* is a **protozoan parasite** causing gastrointestinal infections, and susceptibility to it is primarily linked to **IgA deficiency**, not phagocyte dysfunction.
- While patients with **immunodeficiencies** can have increased risk, CGD is not specifically associated with *Giardia* infections.
*Streptococcus viridans*
- *Streptococcus viridans* are **catalase-negative bacteria** and cause infections typically in patients with **valvular heart disease** or those undergoing dental procedures, and are not commonly associated with CGD.
- CGD patients are more prone to infections by **catalase-positive organisms**, which this bacterium is not.
*Enterococcus faecalis*
- *Enterococcus faecalis* is a **catalase-negative bacterium** that primarily causes **urinary tract infections** and endocarditis, particularly in hospitalized patients.
- While it can cause opportunistic infections, its catalase-negative status makes it less relevant to the specific phagocytic defect in CGD.
*Streptococcus pyogenes*
- *Streptococcus pyogenes* is a **catalase-negative bacterium** responsible for diseases like strep throat, scarlet fever, and necrotizing fasciitis.
- Susceptibility to *S. pyogenes* is generally not increased in CGD patients due to its **catalase-negative nature**, which allows phagocytes to still effectively kill it.
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