Hospital-acquired infections US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Hospital-acquired infections. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Hospital-acquired infections US Medical PG Question 1: The surgical equipment used during a craniectomy is sterilized using pressurized steam at 121°C for 15 minutes. Reuse of these instruments can cause transmission of which of the following pathogens?
- A. Non-enveloped viruses
- B. Sporulating bacteria
- C. Prions (Correct Answer)
- D. Enveloped viruses
- E. Yeasts
Hospital-acquired infections Explanation: ***Prions***
- Prions are **abnormally folded proteins** that are highly resistant to standard sterilization methods like steam autoclaving at 121°C, making them a risk for transmission through reused surgical instruments.
- They cause transmissible spongiform encephalopathies (TSEs) like **Creutzfeldt-Jakob disease**, where even trace amounts can be highly infectious.
*Non-enveloped viruses*
- Non-enveloped viruses are generally **more resistant to heat and disinfectants** than enveloped viruses but are typically inactivated by recommended steam sterilization protocols.
- Standard autoclaving conditions are effective in destroying most non-enveloped viruses.
*Sporulating bacteria*
- **Bacterial spores**, such as those from *Clostridium* or *Bacillus*, are known for their high resistance to heat and chemicals, but are usually **inactivated by steam sterilization at 121°C** for 15 minutes.
- This method is specifically designed to kill bacterial spores effectively.
*Enveloped viruses*
- Enveloped viruses are the **least resistant to heat and chemical disinfectants** due to their lipid envelope.
- They are readily **inactivated by standard steam sterilization** at 121°C.
*Yeasts*
- **Yeasts** are eukaryotic microorganisms that are typically **susceptible to heat sterilization**.
- They are effectively killed by typical steam autoclaving conditions used for surgical instruments.
Hospital-acquired infections US Medical PG Question 2: A 33-year-old woman presents to the urgent care center with 4 days of abdominal pain and increasingly frequent bloody diarrhea. She states that she is currently having 6 episodes of moderate volume diarrhea per day with streaks of blood mixed in. Her vital signs include: blood pressure 121/81 mm Hg, heart rate 77/min, and respiratory rate 15/min. Physical examination is largely negative. Given the following options, which is the most likely pathogen responsible for her presentation?
- A. Campylobacter
- B. Shigella (Correct Answer)
- C. Salmonella
- D. Clostridium difficile
- E. E. coli O157:H7
Hospital-acquired infections Explanation: ***Shigella***
- **Shigella** infection commonly presents with sudden onset of high fever, **abdominal cramps**, and **bloody, watery diarrhea**, often with a small volume.
- The patient's presentation of 4 days of abdominal pain and increasingly frequent **bloody diarrhea** with **6 episodes per day** is highly characteristic of shigellosis.
*Campylobacter*
- **Campylobacter** infection often manifests with **bloody diarrhea**, but it typically presents with preceding **fever** and **malaise**, followed by diarrhea that can be bloody.
- While it can cause bloody diarrhea, the progression described in the patient (increasingly frequent and bloody) might be more indicative of other bacterial dysenteries.
*E. coli 0157:H7*
- **E. coli O157:H7** is a common cause of **hemorrhagic colitis**, characterized by **severe abdominal cramps** and **bloody diarrhea** without significant fever.
- However, its association with **hemolytic uremic syndrome (HUS)**, especially in children, makes it a concern, and while it *can* cause this presentation, other options are more likely given the pure dysenteric picture.
*Salmonella*
- **Salmonella** gastroenteritis typically causes **non-bloody diarrhea**, fever, and abdominal cramps.
- While some serotypes can cause invasive disease and bloody stool, the classic presentation is usually **watery diarrhea**.
*Clostridium difficile*
- **Clostridium difficile** infection is usually associated with **recent antibiotic use** or hospitalization, and commonly causes **foul-smelling, watery diarrhea**, which can occasionally be bloody in severe cases.
- The patient's history does not mention recent antibiotic use, and the presentation of increasingly frequent and bloody diarrhea makes other pathogens more likely.
Hospital-acquired infections US Medical PG Question 3: A 33-year-old female comes to her primary care physician with complaints of fatigue and nausea. She has also noticed that her skin tone is darker than it used to be. On exam, the physician notes that the woman appears to be jaundiced and obtains liver enzymes which demonstrate an elevated AST and ALT. Further testing subsequently confirms the diagnosis of hepatitis B (HBV). The woman is extremely concerned about transmitting this disease to her loved ones and ask how HBV is transmitted. By which of the following routes can HBV be spread? (I) blood, (II) sexual contact, (III) maternal-fetal, and/or (IV) breast milk?
- A. II, III
- B. I, II, III, IV
- C. I, II, III (Correct Answer)
- D. I, III, IV
- E. I only
Hospital-acquired infections Explanation: ***I, II, III***
- **Hepatitis B virus (HBV)** is primarily transmitted through contact with infected **blood** or other bloody body fluids (e.g., semen, vaginal secretions), making routes I (blood) and II (sexual contact) major modes of transmission.
- **Maternal-fetal transmission** (route III) can occur during childbirth, especially if the mother has high viral loads, although *in utero* transmission is rare.
*II, III*
- This option is incorrect because it omits **blood transmission (I)**, which is a major route for HBV spread through shared needles, transfusions, or open wounds.
- While sexual and maternal-fetal transmissions are significant, they do not account for all primary modes of spread.
*I, II, III, IV*
- This option is incorrect because while routes I, II, and III are valid, **breast milk (IV)** is generally *not* considered a significant route for HBV transmission.
- Studies have shown a very low, if any, risk of HBV transmission through breast milk, and breastfeeding is typically safe for HBV-positive mothers, especially if the infant is vaccinated.
*I, III, IV*
- This option is incorrect because it includes **breast milk (IV)**, which is not a clinically significant route of transmission, and it excludes **sexual contact (II)**, a very common mode of HBV spread.
- Many HBV infections are acquired through unprotected sexual intercourse with an infected partner.
*I only*
- This option is incorrect as it severely underrepresents the various transmission routes of HBV, omitting **sexual contact (II)** and **maternal-fetal transmission (III)**.
- While blood transmission is critical, HBV is also frequently spread through other bodily fluids and from mother to child.
Hospital-acquired infections US Medical PG Question 4: A 65-year-old woman undergoes an abdominal hysterectomy. She develops pain and discharge at the incision site on the fourth postoperative day. The past medical history is significant for diabetes of 12 years duration, which is well-controlled on insulin. Pus from the incision site is sent for culture on MacConkey agar, which shows white-colorless colonies. On blood agar, the colonies were green. Biochemical tests reveal an oxidase-positive organism. Which of the following is the most likely pathogen?
- A. Staphylococcus aureus
- B. Enterococcus faecalis
- C. Streptococcus pyogenes
- D. Pseudomonas aeruginosa (Correct Answer)
- E. Staphylococcus epidermidis
Hospital-acquired infections Explanation: ***Pseudomonas aeruginosa***
- The combination of **white, colorless colonies on MacConkey agar** (indicating a non-lactose fermenter), **green colonies on blood agar** (due to pigment production), and a **positive oxidase test** is highly characteristic of *Pseudomonas aeruginosa*.
- This organism is a common cause of **nosocomial infections**, particularly in immunocompromised patients (like those with diabetes) and in postoperative wound infections.
*Staphylococcus aureus*
- This bacterium would typically produce **golden-yellow colonies** on blood agar and **no growth on MacConkey agar**.
- It is **oxidase-negative** and a common cause of surgical site infections, but its colonial morphology and biochemical tests do not match the description.
*Enterococcus faecalis*
- This organism is a **Gram-positive coccus** that would not grow well on MacConkey agar and would not produce green colonies on blood agar or be oxidase-positive.
- It is a common cause of urinary tract and wound infections, especially in hospitalized patients.
*Streptococcus pyogenes*
- This is a **beta-hemolytic Streptococcus** that typically produces small, clear colonies with a zone of complete hemolysis on blood agar and would not grow on MacConkey agar.
- It is also **oxidase-negative**, making it inconsistent with the findings.
*Staphylococcus epidermidis*
- This organism forms **white colonies** on blood agar and would not grow on MacConkey agar or produce green pigment.
- It is **coagulase-negative** and **oxidase-negative**, and while it can cause surgical site infections, its colonial characteristics differ.
Hospital-acquired infections US Medical PG Question 5: A 62-year-old man is brought to the emergency department with fatigue, dry cough, and shortness of breath for 3 days. He reports a slight fever and has also had 3 episodes of watery diarrhea earlier that morning. Last week, he attended a business meeting at a hotel and notes some of his coworkers have also become sick. He has a history of hypertension and hyperlipidemia. He takes atorvastatin, hydrochlorothiazide, and lisinopril. He appears in mild distress. His temperature is 102.1°F (38.9°C), pulse is 56/min, respirations are 16/min, and blood pressure is 150/85 mm Hg. Diffuse crackles are heard in the thorax. Examination shows a soft and nontender abdomen. Laboratory studies show:
Hemoglobin 13.5 g/dL
Leukocyte count 15,000/mm3
Platelet count 130,000/mm3
Serum
Na+ 129 mEq/L
Cl- 100 mEq/L
K+ 4.6 mEq/L
HCO3- 22 mEq/L
Urea nitrogen 14 mg/dL
Creatinine 1.3 mg/dL
An x-ray of the chest shows infiltrates in both lungs. Which of the following is the most appropriate next step in diagnosis?
- A. Urine antigen assay (Correct Answer)
- B. CT Chest
- C. Direct immunofluorescent antibody test
- D. Stool culture
- E. Polymerase chain reaction
Hospital-acquired infections Explanation: ***Urine antigen assay***
- This patient presents with **pneumonia symptoms** (low-grade fever, dry cough, dyspnea, bilateral infiltrates) along with **gastrointestinal symptoms** (watery diarrhea) and **hyponatremia**, after attending a hotel meeting with other sick attendees. These are classic features of **Legionnaires' disease**.
- A **urine antigen assay** is a rapid and highly specific test for **Legionella pneumophila serogroup 1**, which causes the majority of Legionnaires' disease cases.
*CT Chest*
- A CT scan of the chest would provide more detailed imaging of the lung infiltrates but is typically used to characterize findings once pneumonia is diagnosed or to rule out other lung pathologies, not as an initial diagnostic test for the specific pathogen.
- While it can reveal characteristic patterns, it doesn't identify the causative organism and is not the most appropriate *next step in diagnosis* for a presumed Legionella infection.
*Direct immunofluorescent antibody test*
- A **direct immunofluorescent antibody (DFA) test** is used to identify legionella in respiratory secretions. However, collecting a sufficiently good sputum sample can be difficult, especially with a **dry cough**.
- Its sensitivity is lower than urine antigen testing for serogroup 1 and requires a respiratory sample, making it less convenient for initial diagnosis.
*Stool culture*
- While the patient has diarrhea, a **stool culture** would primarily detect typical bacterial enteric pathogens (e.g., Salmonella, Shigella, Campylobacter) and would not identify **Legionella**.
- The diarrhea, in this context, is likely an extrapulmonary manifestation of Legionnaires' disease caused by Legionella, not a separate primary enteric infection.
*Polymerase chain reaction*
- **PCR testing** can detect Legionella DNA in respiratory samples, offering high sensitivity and specificity.
- However, it is generally less rapid and widely available than the urine antigen test for initial diagnosis of Legionella pneumophila serogroup 1, which is the most common cause of Legionnaires' disease.
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