An 18-year-old girl is brought to the emergency department because of a 1-day history of severe headache with photophobia and diffuse myalgias. She is a college student and lives in a dormitory in a large urban area. She has not traveled recently. On arrival, she is lethargic. Her temperature is 39.3°C (102.7°F), pulse is 120/min, and blood pressure is 88/58 mm Hg. Examination shows scattered petechiae and ecchymoses on the trunk and lower extremities. There is decreased range of motion of the neck. Cerebrospinal fluid analysis shows a cell count of 1,600/μL (80% neutrophils) and a lactate concentration of 5.1 mmol/L. Which of the following is most likely to have prevented this patient's condition?
Q2
An 18-month-old boy presents to the emergency department for malaise. The boy’s parents report worsening fatigue for 3 days with associated irritability and anorexia. The patient’s newborn screening revealed a point mutation in the beta-globin gene but the patient has otherwise been healthy since birth. On physical exam, his temperature is 102.4°F (39.1°C), blood pressure is 78/42 mmHg, pulse is 124/min, and respirations are 32/min. The child is tired-appearing and difficult to soothe. Laboratory testing is performed and reveals the following:
Serum:
Na+: 137 mEq/L
Cl-: 100 mEq/L
K+: 4.4 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 16 mg/dL
Creatinine: 0.9 mg/dL
Glucose: 96 mg/dL
Leukocyte count: 19,300/mm^3 with normal differential
Hemoglobin: 7.8 g/dL
Hematocrit: 21%
Mean corpuscular volume: 82 um^3
Platelet count: 324,000/mm^3
Reticulocyte index: 3.6%
Which of the following is the most likely causative organism for this patient's presentation?
Q3
A 15-year-old boy is brought to the Emergency department by ambulance from school. He started the day with some body aches and joint pain but then had several episodes of vomiting and started complaining of a terrible headache. The school nurse called for emergency services. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. Past medical history is noncontributory. He is a good student and enjoys sports. At the hospital, his blood pressure is 120/80 mm Hg, heart rate is 105/min, respiratory rate is 21/min, and his temperature is 38.9°C (102.0°F). On physical exam, he appears drowsy with neck stiffness and sensitivity to light. Kernig’s sign is positive. An ophthalmic exam is performed followed by a lumbar puncture. An aliquot of cerebrospinal fluid is sent to microbiology. A gram stain shows gram-negative diplococci. A smear is prepared on blood agar and grows round, smooth, convex colonies with clearly defined edges. Which of the following would identify the described pathogen?
Q4
A 71-year-old woman presents with high-grade fever and chills, difficulty breathing, and a productive cough with rust-colored sputum. She complains of a sharp left-sided chest pain. Physical examination reveals increased fremitus, dullness to percussion, and bronchial breath sounds on the lower left side. A chest X-ray shows left lower lobe consolidation. The offending organism that was cultured from the sputum was catalase-negative and had a positive Quellung reaction. The organism will show which gram stain results?
Q5
You are seeing a 4-year-old boy in clinic who is presenting with concern for a primary immune deficiency. He has an unremarkable birth history, but since the age of 6 months he has had recurrent otitis media, bacterial pneumonia, as well as two episodes of sinusitis, and four episodes of conjunctivitis. He has a maternal uncle who died from sepsis secondary to H. influenza pneumonia. If you drew blood work for diagnostic testing, which of the following would you expect to find?
Q6
An 8-year-old girl is brought to the emergency room for a 6-hour history of fever, sore throat, and difficulty swallowing. Physical examination shows pooling of oral secretions and inspiratory stridor. Lateral x-ray of the neck shows thickening of the epiglottis and aryepiglottic folds. Throat culture with chocolate agar shows small, gram-negative coccobacilli. The patient's brother is started on the recommended antibiotic for chemoprophylaxis. Which of the following is the primary mechanism of action of this drug?
Q7
A 27-year-old woman presents to the clinic with severe pain in her left knee of 1-day duration. Physical examination reveals a red, swollen, warm, and tender left knee with a decreased range of motion. The patient affirms that she has been sexually active with several partners over the last year and that 1 of her partners has complained of dysuria and yellow urethral discharge. An arthrocentesis was performed and showed a WBC count of 60,000/µL, with 90% polymorphonuclear leukocytes. Visualization of the patient's synovial fluid is provided in the image. Which of the following is a characteristic feature of the organism causing this condition?
Q8
While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?
Q9
A 2-year-old girl who emigrated from Pakistan 2 weeks ago is brought to the emergency department because of lower limb weakness for one-day. One week ago, she had a 3-day episode of flu-like symptoms that resolved without treatment. She has not yet received any routine childhood vaccinations. Deep tendon reflexes are 1+ in the right lower extremity and absent in the left lower extremity. Analysis of cerebrospinal fluid shows a leukocyte count of 38 cells/mm3 (68% lymphocytes), a protein concentration of 49 mg/dL, and a glucose concentration of 60 mg/dL. Which of the following is the most likely diagnosis in this patient?
Q10
An 18-year-old female college student is brought to the emergency department by ambulance for a headache and altered mental status. The patient lives with her boyfriend who is with her currently. He states she had not been feeling well for the past day and has vomited several times in the past 12 hours. Lumbar puncture is performed in the emergency room and demonstrates an increased cell count with a neutrophil predominance and gram-negative diplococci on Gram stain. The patient is started on vancomycin and ceftriaxone. Which of the following is the best next step in management?
Haemophilus influenzae US Medical PG Practice Questions and MCQs
Question 1: An 18-year-old girl is brought to the emergency department because of a 1-day history of severe headache with photophobia and diffuse myalgias. She is a college student and lives in a dormitory in a large urban area. She has not traveled recently. On arrival, she is lethargic. Her temperature is 39.3°C (102.7°F), pulse is 120/min, and blood pressure is 88/58 mm Hg. Examination shows scattered petechiae and ecchymoses on the trunk and lower extremities. There is decreased range of motion of the neck. Cerebrospinal fluid analysis shows a cell count of 1,600/μL (80% neutrophils) and a lactate concentration of 5.1 mmol/L. Which of the following is most likely to have prevented this patient's condition?
A. Intravenous vancomycin
B. Polysaccharide conjugate vaccine (Correct Answer)
C. Erythromycin therapy
D. Doxycycline therapy
E. Toxoid vaccine
Explanation: ***Polysaccharide conjugate vaccine***
- This patient presents with symptoms highly suggestive of **bacterial meningitis** and **septic shock**, likely caused by *Neisseria meningitidis*, given the petechiae, ecchymoses, and rapid deterioration.
- A **meningococcal conjugate vaccine** would have provided protection against most common serogroups of *N. meningitidis* (A, C, W-135, Y) and is strongly recommended for college students living in dormitories due to increased risk of transmission.
*Intravenous vancomycin*
- This is an **acute treatment** for bacterial meningitis, specifically active against *Streptococcus pneumoniae* and some resistant strains.
- It would not have **prevented** the condition; preventative measures are typically vaccines or prophylactic antibiotics.
*Erythromycin therapy*
- Erythromycin is an antibiotic used for various bacterial infections, including atypical pneumonia and some skin infections.
- It is **not the primary prophylactic agent** for meningococcal disease and would not have prevented this specific condition.
*Doxycycline therapy*
- Doxycycline is a broad-spectrum antibiotic used for a range of infections, including tick-borne diseases and certain respiratory infections.
- It is **not indicated for the prevention** of meningococcal meningitis.
*Toxoid vaccine*
- **Toxoid vaccines** protect against diseases caused by bacterial toxins, such as tetanus and diphtheria.
- *Neisseria meningitidis* causes disease primarily through direct invasion and immune response to its capsular polysaccharides, not primarily exotoxins, so a toxoid vaccine would not be effective here.
Question 2: An 18-month-old boy presents to the emergency department for malaise. The boy’s parents report worsening fatigue for 3 days with associated irritability and anorexia. The patient’s newborn screening revealed a point mutation in the beta-globin gene but the patient has otherwise been healthy since birth. On physical exam, his temperature is 102.4°F (39.1°C), blood pressure is 78/42 mmHg, pulse is 124/min, and respirations are 32/min. The child is tired-appearing and difficult to soothe. Laboratory testing is performed and reveals the following:
Serum:
Na+: 137 mEq/L
Cl-: 100 mEq/L
K+: 4.4 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 16 mg/dL
Creatinine: 0.9 mg/dL
Glucose: 96 mg/dL
Leukocyte count: 19,300/mm^3 with normal differential
Hemoglobin: 7.8 g/dL
Hematocrit: 21%
Mean corpuscular volume: 82 um^3
Platelet count: 324,000/mm^3
Reticulocyte index: 3.6%
Which of the following is the most likely causative organism for this patient's presentation?
A. Streptococcus pneumoniae (Correct Answer)
B. Listeria monocytogenes
C. Haemophilus influenzae
D. Neisseria meningitidis
E. Salmonella
Explanation: ***Streptococcus pneumoniae***
- Patients with **sickle cell disease** (indicated by the beta-globin gene mutation) are functionally **asplenic** and highly susceptible to encapsulated bacteria, with *S. pneumoniae* being the most common cause of **sepsis** in this population.
- The patient's presentation with **fever**, **hypotension**, **tachycardia**, and **leukocytosis** is consistent with **sepsis**, and the elevated reticulocyte index suggests a hemolytic process or bone marrow response, common in sickle cell crises exacerbated by infection.
*Listeria monocytogenes*
- This pathogen primarily affects **neonates**, **immunocompromised individuals**, and **elderly** patients, often presenting as meningitis or sepsis.
- While it can cause sepsis, it is a less common cause of severe infection in a non-neonatal toddler with sickle cell disease compared to *S. pneumoniae*.
*Haemophilus influenzae*
- Although *H. influenzae* is an encapsulated bacterium that can cause severe infections in functionally asplenic patients, routine childhood vaccinations have significantly reduced its incidence.
- While possible, it is less likely than *S. pneumoniae* in an 18-month-old, especially if vaccinated, and *S. pneumoniae* remains the leading cause of sepsis in sickle cell patients.
*Neisseria meningitidis*
- *N. meningitidis* is another encapsulated bacterium that can cause serious infections, including **meningitis** and **sepsis**, particularly in immunocompromised individuals like those with sickle cell disease.
- However, the incidence of **meningococcal disease** is generally lower than **pneumococcal disease** in this age group, and the absence of classic meningeal signs or petechial rash makes it a less probable primary suspect compared to *S. pneumoniae*.
*Salmonella*
- *Salmonella* species can cause **osteomyelitis** and **sepsis** in patients with sickle cell disease, often presenting with gastrointestinal symptoms.
- While a known pathogen in this population, the clinical picture of **rapidly progressive sepsis** without clear GI focus makes *S. pneumoniae* a more immediate and common concern.
Question 3: A 15-year-old boy is brought to the Emergency department by ambulance from school. He started the day with some body aches and joint pain but then had several episodes of vomiting and started complaining of a terrible headache. The school nurse called for emergency services. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. Past medical history is noncontributory. He is a good student and enjoys sports. At the hospital, his blood pressure is 120/80 mm Hg, heart rate is 105/min, respiratory rate is 21/min, and his temperature is 38.9°C (102.0°F). On physical exam, he appears drowsy with neck stiffness and sensitivity to light. Kernig’s sign is positive. An ophthalmic exam is performed followed by a lumbar puncture. An aliquot of cerebrospinal fluid is sent to microbiology. A gram stain shows gram-negative diplococci. A smear is prepared on blood agar and grows round, smooth, convex colonies with clearly defined edges. Which of the following would identify the described pathogen?
A. Oxidase-positive and ferments glucose and maltose (Correct Answer)
B. Oxidase-positive test and ferments glucose only
C. Catalase-negative and oxidase-positive
D. No growth on Thayer-Martin medium
E. Growth in anaerobic conditions
Explanation: ***Oxidase-positive and ferments glucose and maltose***
- The patient's symptoms (fever, headache, neck stiffness, sensitivity to light, positive Kernig's sign) are classic for **meningitis**, and the CSF showing **gram-negative diplococci** points to *Neisseria meningitidis*.
- *Neisseria meningitidis* is identified by its positive **oxidase test** and its ability to ferment both **glucose and maltose**.
*Oxidase-positive test and ferments glucose only*
- This description corresponds to *Neisseria gonorrhoeae*, which primarily causes **gonorrhea** and occasionally meningitis due to disseminated infection but is less common in this age group and presentation.
- While *Neisseria gonorrhoeae* is also an **oxidase-positive gram-negative diplococcus**, it specifically ferments only *glucose*, not maltose.
*Catalase-negative and oxidase-positive*
- While *Neisseria meningitidis* is **oxidase-positive**, stating it is "catalase-negative" is incorrect; *Neisseria* species are actually **catalase-positive**.
- This option incorrectly describes a general metabolic property that would rule out *Neisseria meningitidis*.
*No growth on Thayer-Martin medium*
- Thayer-Martin medium is a **selective medium** specifically designed to isolate pathogenic *Neisseria species* by inhibiting the growth of commensal bacteria and fungi.
- Therefore, *Neisseria meningitidis* would **grow well** on Thayer-Martin medium, making "no growth" an incorrect identifier.
*Growth in anaerobic conditions*
- *Neisseria meningitidis* is an **obligate aerobe**, meaning it requires oxygen for growth.
- It would **not grow** in anaerobic conditions, making this statement false for identifying the described pathogen.
Question 4: A 71-year-old woman presents with high-grade fever and chills, difficulty breathing, and a productive cough with rust-colored sputum. She complains of a sharp left-sided chest pain. Physical examination reveals increased fremitus, dullness to percussion, and bronchial breath sounds on the lower left side. A chest X-ray shows left lower lobe consolidation. The offending organism that was cultured from the sputum was catalase-negative and had a positive Quellung reaction. The organism will show which gram stain results?
A. Gram-negative diplococci
B. Cannot be seen with gram staining since the organism lacks a cell wall
C. Gram-positive cocci in clusters
D. Gram-negative rod
E. Gram-positive diplococci (Correct Answer)
Explanation: ***Gram-positive diplococci***
- The clinical presentation (high fever, chills, productive cough with **rust-colored sputum**, sharp chest pain, signs of **consolidation**) is classic for **pneumococcal pneumonia**.
- The organism responsible for pneumococcal pneumonia, *Streptococcus pneumoniae*, is a **Gram-positive, catalase-negative diplococcus** that exhibits a **positive Quellung reaction** due to its polysaccharide capsule.
*Gram-negative diplococci*
- This describes organisms such as **Neisseria meningitidis** or **Neisseria gonorrhoeae**, which cause meningitis or gonorrhea, respectively, not typical pneumonia.
- While *Moraxella catarrhalis* is a Gram-negative diplococcus that can cause respiratory infections, it typically causes otitis media or sinusitis and less commonly severe pneumonia with rust-colored sputum.
*Cannot be seen with gram staining since the organism lacks a cell wall*
- This description typically refers to **Mycoplasma pneumoniae**, which causes **atypical pneumonia** and lacks a cell wall, rendering it unstainable by Gram stain.
- Mycoplasma pneumonia usually presents with a more indolent course, a non-productive cough, and rarely causes rust-colored sputum or lobar consolidation seen on X-ray.
*Gram-positive cocci in clusters*
- This morphology is characteristic of **staphylococci**, such as *Staphylococcus aureus*, which can cause pneumonia, often in immunocompromised individuals or as a complication of influenza.
- However, *Staphylococcus aureus* is **catalase-positive**, and its pneumonia presentation can be more fulminant, often leading to abscess formation, differing from the typical presentation of pneumococcal pneumonia.
*Gram-negative rod*
- This morphology is characteristic of various bacteria including **Klebsiella pneumoniae**, **Pseudomonas aeruginosa**, or **Haemophilus influenzae**.
- **Klebsiella pneumoniae** can cause severe pneumonia with **currant jelly sputum** but is a Gram-negative rod and would not exhibit a Quellung reaction in the same manner as *S. pneumoniae*.
Question 5: You are seeing a 4-year-old boy in clinic who is presenting with concern for a primary immune deficiency. He has an unremarkable birth history, but since the age of 6 months he has had recurrent otitis media, bacterial pneumonia, as well as two episodes of sinusitis, and four episodes of conjunctivitis. He has a maternal uncle who died from sepsis secondary to H. influenza pneumonia. If you drew blood work for diagnostic testing, which of the following would you expect to find?
A. Abnormally low number of T cells
B. Abnormally high number of B cells
C. Elevated immunoglobulin levels
D. Abnormally low number of B cells (Correct Answer)
E. Abnormally high number of T cells
Explanation: ***Abnormally low number of B cells***
- The recurrent bacterial infections (otitis media, pneumonia, sinusitis, conjunctivitis) and the family history of death from *H. influenza* pneumonia suggest a **primary B-cell immunodeficiency**, such as **X-linked agammaglobulinemia (XLA)**.
- In XLA, there is a block in B-cell development, leading to a profound absence of mature B cells and immunoglobulins.
*Abnormally low number of T cells*
- This would point towards a **T-cell immunodeficiency** or a **combined immunodeficiency**, typically presenting with opportunistic infections, viral, or fungal infections, rather than predominantly bacterial infections.
- Examples include **Severe Combined Immunodeficiency (SCID)**, which often presents earlier and more severely.
*Abnormally high number of B cells*
- This is not characteristic of a primary immunodeficiency with recurrent bacterial infections; rather, it might be seen in certain autoimmune conditions or lymphoproliferative disorders.
- **High B cell counts** generally imply a functioning humoral immune system, which contradicts the infectious history.
*Elevated immunoglobulin levels*
- This finding would generally indicate a **functioning humoral immune response**, possibly due to chronic infection or an inflammatory process, but not a primary B-cell immunodeficiency causing recurrent bacterial infections.
- In conditions like **Common Variable Immunodeficiency (CVID)**, some immunoglobulin levels might be normal, but often key classes (like IgG, IgA, or IgM) are low.
*Abnormally high number of T cells*
- This finding is generally not associated with the pattern of recurrent bacterial infections described, which strongly points to a **humoral (antibody) deficiency**.
- **Elevated T cells** could be seen in some autoimmune conditions or certain viral infections, but not typically in a primary immunodeficiency characterized by recurrent bacterial infections.
Question 6: An 8-year-old girl is brought to the emergency room for a 6-hour history of fever, sore throat, and difficulty swallowing. Physical examination shows pooling of oral secretions and inspiratory stridor. Lateral x-ray of the neck shows thickening of the epiglottis and aryepiglottic folds. Throat culture with chocolate agar shows small, gram-negative coccobacilli. The patient's brother is started on the recommended antibiotic for chemoprophylaxis. Which of the following is the primary mechanism of action of this drug?
A. Inhibition of the 50S ribosomal subunit
B. Inhibition of prokaryotic topoisomerase II
C. Inhibition of DNA-dependent RNA-polymerase (Correct Answer)
D. Inhibition of the 30S ribosomal subunit
E. Inhibition of peptidoglycan crosslinking
Explanation: ***Inhibition of DNA-dependent RNA-polymerase***
- The clinical picture strongly suggests **epiglottitis** caused by *Haemophilus influenzae type b* (Hib), characterized by **fever, sore throat, difficulty swallowing, pooling of oral secretions, inspiratory stridor**, and **epiglottic thickening** on X-ray.
- **Rifampin** is the recommended antibiotic for chemoprophylaxis in close contacts of Hib patients; its primary mechanism of action is to inhibit bacterial **DNA-dependent RNA polymerase**, thereby preventing **mRNA synthesis**.
*Inhibition of the 50S ribosomal subunit*
- This mechanism is characteristic of **macrolides** (e.g., azithromycin, erythromycin) and **clindamycin**, which are not the primary choice for Hib chemoprophylaxis.
- These drugs prevent **protein synthesis** by interfering with translocation or peptide bond formation on the larger ribosomal subunit.
*Inhibition of prokaryotic topoisomerase II*
- This is the mechanism of action for **fluoroquinolones** (e.g., ciprofloxacin), which are typically reserved for specific infections due to potential side effects in children.
- Fluoroquinolones interfere with **DNA replication** and **transcription** by preventing DNA unwinding and supercoiling.
*Inhibition of the 30S ribosomal subunit*
- This mechanism is associated with **tetracyclines** and **aminoglycosides** (e.g., doxycycline, gentamicin).
- These antibiotics block **protein synthesis** by preventing tRNA attachment or causing misreading of mRNA.
*Inhibition of peptidoglycan crosslinking*
- This describes the mechanism of **beta-lactam antibiotics** (e.g., penicillin, amoxicillin, cephalosporins), which inhibit bacterial **cell wall synthesis**.
- While some beta-lactams are used to treat Hib infections, they are not the primary drug for **chemoprophylaxis**.
Question 7: A 27-year-old woman presents to the clinic with severe pain in her left knee of 1-day duration. Physical examination reveals a red, swollen, warm, and tender left knee with a decreased range of motion. The patient affirms that she has been sexually active with several partners over the last year and that 1 of her partners has complained of dysuria and yellow urethral discharge. An arthrocentesis was performed and showed a WBC count of 60,000/µL, with 90% polymorphonuclear leukocytes. Visualization of the patient's synovial fluid is provided in the image. Which of the following is a characteristic feature of the organism causing this condition?
A. It causes the Jarisch-Herxheimer reaction when treated with penicillin
B. It produces a heat-labile toxin that prevents protein synthesis
C. It selectively grows on Thayer-Martin medium (Correct Answer)
D. It is a gram-positive diplococcus
E. It ferments maltose
Explanation: ***It selectively grows on Thayer-Martin medium***
- The patient's presentation with **septic arthritis**, a history of multiple sexual partners, and a partner with symptoms of **urethritis** suggests **gonococcal arthritis** caused by *Neisseria gonorrhoeae*.
- *Neisseria gonorrhoeae* is a fastidious organism that requires an enriched selective medium like **Thayer-Martin agar** for optimal growth, which contains antimicrobial agents to inhibit commensal flora.
*It causes the Jarisch-Herxheimer reaction when treated with penicillin*
- The **Jarisch-Herxheimer reaction** is typically associated with treatment of **spirochetal diseases** like **syphilis** (caused by *Treponema pallidum)* or **Lyme disease** (caused by *Borrelia burgdorferi*) with penicillin.
- This reaction results from the rapid lysis of spirochetes and the release of endotoxins, which is not characteristic of gonococcal infection or its treatment.
*It produces a heat-labile toxin that prevents protein synthesis*
- This description is characteristic of toxins produced by organisms like **diphtheria toxin** (*Corynebacterium diphtheriae*) or **Shiga toxin** (*Shigella dysenteriae* and enterohemorrhagic *E. coli*), which inhibit protein synthesis but are not associated with *Neisseria gonorrhoeae*.
- *Neisseria gonorrhoeae* possesses virulence factors like pili, Opa proteins, and LOS, but its primary pathogenicity mechanism does not involve a heat-labile toxin that prevents protein synthesis.
*It is a gram-positive diplococcus*
- The image clearly shows **gram-negative diplococci** within phagocytes (neutrophils), which is a classic microscopic finding for *Neisseria gonorrhoeae*.
- *Neisseria gonorrhoeae* is specifically a **Gram-negative organism**, not Gram-positive.
*It ferments maltose*
- *Neisseria gonorrhoeae* metabolizes **glucose only** and does not ferment maltose, which helps differentiate it from *Neisseria meningitidis* (which ferments both glucose and maltose).
- This metabolic characteristic is a key biochemical test used in the laboratory for the identification of *Neisseria* species.
Question 8: While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?
A. Quellung reaction (Correct Answer)
B. Hemolytic reaction when grown on sheep blood agar
C. Bile solubility
D. Optochin sensitivity
E. Motility
Explanation: ***Quellung reaction***
- The **Quellung reaction** tests for the presence of the **polysaccharide capsule**, which is the primary virulence factor of *S. pneumoniae*.
- An **avirulent strain** that cannot cause disease would most likely lack the capsule and show a **negative Quellung reaction** (no capsular swelling), deviating from the **positive reaction** seen in typical encapsulated pathogenic strains.
- The capsule enables *S. pneumoniae* to evade phagocytosis and complement-mediated killing, which is essential for establishing infection in the lungs.
*Hemolytic reaction when grown on sheep blood agar*
- Both virulent and avirulent strains of *S. pneumoniae* typically exhibit **alpha-hemolysis** (partial hemolysis, producing a greenish discoloration) on sheep blood agar due to the production of pneumolysin.
- This characteristic does not differentiate between pathogenic and non-pathogenic strains in terms of disease-causing ability.
*Bile solubility*
- *S. pneumoniae* is characteristically **bile-soluble** due to the presence of autolysin enzymes that are activated by bile salts, leading to cellular lysis.
- This property is a **species characteristic** present in both virulent and avirulent strains, thus it would not explain the inability to cause disease.
*Optochin sensitivity*
- *S. pneumoniae* is universally **sensitive to optochin**, a chemical agent that inhibits its growth and is used for laboratory identification.
- This characteristic is used for **species identification** but does not correlate with strain virulence or disease-causing ability.
*Motility*
- *Streptococcus pneumoniae* is a **non-motile** bacterium; it lacks flagella.
- This characteristic is consistent across all strains and is not a virulence factor for this species.
Question 9: A 2-year-old girl who emigrated from Pakistan 2 weeks ago is brought to the emergency department because of lower limb weakness for one-day. One week ago, she had a 3-day episode of flu-like symptoms that resolved without treatment. She has not yet received any routine childhood vaccinations. Deep tendon reflexes are 1+ in the right lower extremity and absent in the left lower extremity. Analysis of cerebrospinal fluid shows a leukocyte count of 38 cells/mm3 (68% lymphocytes), a protein concentration of 49 mg/dL, and a glucose concentration of 60 mg/dL. Which of the following is the most likely diagnosis in this patient?
A. Poliomyelitis (Correct Answer)
B. Tetanus
C. Guillain-Barre syndrome
D. Botulism
E. HSV encephalitis
Explanation: ***Poliomyelitis***
- The patient's presentation with **acute flaccid paralysis** (lower limb weakness with absent reflexes), recent emigration from a region with potential **endemic polio** (Pakistan), and **lack of vaccination** are highly suggestive of poliomyelitis.
- The **CSF findings** (mild pleocytosis with lymphocytic predominance and normal glucose) are consistent with a viral infection of the central nervous system, which is characteristic of polio.
*Tetanus*
- Tetanus typically presents with **spastic paralysis**, muscle rigidity, and **lockjaw**, not flaccid paralysis.
- The onset of symptoms is also usually preceded by a wound contamination, which is not mentioned in this case.
*Guillain-Barre syndrome*
- While GBS can cause **flaccid paralysis** and is often preceded by a viral illness, it typically presents with **ascending paralysis** and the CSF classically shows **albumino-cytological dissociation** (high protein with normal or low cell count), which is not fully consistent with the CSF findings here.
- The rapid onset of significant asymmetry in reflexes is also less typical for GBS.
*Botulism*
- Botulism causes **descending flaccid paralysis**, often starting with cranial nerve palsies (e.g., ptosis, diplopia), and is typically associated with ingestion of contaminated food or honey in infants.
- The patient's symptoms are more focused on lower limb weakness without initial cranial nerve involvement, and the CSF findings are usually normal in botulism.
*HSV encephalitis*
- HSV encephalitis typically presents with **fever, seizures, altered mental status, and focal neurological deficits**, not primarily acute flaccid paralysis.
- While it is a viral encephalitis, the predominant symptom pattern and the specific lower limb weakness are not characteristic of HSV encephalitis.
Question 10: An 18-year-old female college student is brought to the emergency department by ambulance for a headache and altered mental status. The patient lives with her boyfriend who is with her currently. He states she had not been feeling well for the past day and has vomited several times in the past 12 hours. Lumbar puncture is performed in the emergency room and demonstrates an increased cell count with a neutrophil predominance and gram-negative diplococci on Gram stain. The patient is started on vancomycin and ceftriaxone. Which of the following is the best next step in management?
A. Treat boyfriend with rifampin (Correct Answer)
B. Add ampicillin to treatment regimen
C. Add ampicillin, dexamethasone, and rifampin to treatment regimen
D. Add dexamethasone to treatment regimen
E. Treat boyfriend with ceftriaxone and vancomycin
Explanation: ***Treat boyfriend with rifampin***
- The patient's presentation with headache, altered mental status, neutrophilic pleocytosis, and **Gram-negative diplococci** on CSF Gram stain is highly suggestive of **Neisseria meningitidis** meningitis.
- The patient is already on appropriate empiric antibiotic therapy (vancomycin and ceftriaxone), so the **immediate priority** is to prevent secondary cases through **post-exposure prophylaxis** for close contacts.
- Close contacts, including household members like the boyfriend, are at high risk of contracting the infection and should receive prophylaxis within **24 hours** of case identification, with **rifampin**, **ciprofloxacin**, or **IM ceftriaxone** being standard options.
*Add ampicillin to treatment regimen*
- Ampicillin provides coverage for **Listeria monocytogenes**, but the Gram stain demonstrating **Gram-negative diplococci** makes Listeria (Gram-positive rod) unlikely in this otherwise healthy young adult without specific risk factors for Listeria.
- The current regimen of vancomycin and ceftriaxone provides adequate empiric coverage for acute bacterial meningitis, targeting common pathogens like **S. pneumoniae** and **N. meningitidis**.
*Add ampicillin, dexamethasone, and rifampin to treatment regimen*
- While providing rifampin prophylaxis to the boyfriend is appropriate, adding it to the **patient's** treatment regimen is not indicated for her active infection.
- **Dexamethasone** is often added to reduce inflammation and neurological sequelae but should be given **prior to or concurrently** with the first dose of antibiotics; adding it later in the course may not be as beneficial.
- This option conflates treatment of the patient with prophylaxis of contacts.
*Add dexamethasone to treatment regimen*
- Dexamethasone is recommended in adults with suspected pneumococcal meningitis to reduce mortality and neurological sequelae, but ideal administration is **prior to or with the first dose of antibiotics**.
- While it might still be considered, the priority given the **Gram-negative diplococci** (suggesting N. meningitidis rather than S. pneumoniae) is **contact prophylaxis** to prevent further spread, and the timing for optimal dexamethasone benefit has likely passed.
*Treat boyfriend with ceftriaxone and vancomycin*
- Ceftriaxone and vancomycin are appropriate for treating the patient's active meningitis, but they are not the standard or preferred agents for **post-exposure prophylaxis** in contacts.
- Post-exposure prophylaxis typically involves a short course of agents like **rifampin**, **ciprofloxacin**, or a single dose of **intramuscular ceftriaxone**, primarily to eradicate nasopharyngeal carriage and prevent transmission.
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