Hospital-acquired infections

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.

Hospital-acquired infections US Medical PG Question 6: A 25-year-old construction worker presents to the office due to a yellowish discoloration of his skin and eyes for the past 2 weeks. He also complains of nausea and loss of appetite for the same duration. The past medical history is insignificant. He is a smoker, but recently has grown a distaste for smoking. The vital signs include: heart rate 83/min, respiratory rate 13/min, temperature 36.5°C (97.7°F), and blood pressure 111/74 mm Hg. On physical examination, there is mild hepatomegaly. The results of the hepatitis viral panel are as follows: Anti-HAV IgM positive HBsAg negative IgM anti-HBc negative Anti-HCV negative HCV-RNA negative Anti-HDV negative Anti-HEV negative What is the most common mode of transmission for this patient’s diagnosis?

• A. Breast milk
• B. Perinatal
• C. Fecal-oral (Correct Answer)
• D. Blood transfusion
• E. Sexual contact

Hospital-acquired infections Explanation: ***Fecal-oral*** - This patient's symptoms (jaundice, nausea, anorexia) and labs (**positive Anti-HAV IgM**) indicate acute **Hepatitis A virus (HAV)** infection - **HAV** is predominantly transmitted via the **fecal-oral route**, often through contaminated food or water - This is the **most common mode** of transmission, particularly in areas with poor sanitation or through contaminated food handlers *Breast milk* - While some viruses can be transmitted via breast milk, it is **not a common mode** of transmission for acute **Hepatitis A** - **HAV** primarily spreads through contaminated ingestion via the fecal-oral route *Perinatal* - **Perinatal transmission** refers to infection from mother to child during pregnancy or childbirth, which is common for viruses like **HBV or HIV** - **HAV** is not typically transmitted **perinatally** and is not a concern during pregnancy in the same way bloodborne viruses are *Blood transfusion* - **Bloodborne pathogens** like **Hepatitis B, C, or HIV** are transmissible through blood transfusions - **Hepatitis A** is an **enteric virus** and is rarely transmitted via blood transfusions, especially with modern screening practices - Viremia in HAV is transient and brief compared to chronic bloodborne hepatitis viruses *Sexual contact* - Although **HAV** can be transmitted through close person-to-person contact, including sexual contact (particularly among men who have sex with men), it is **not its most common mode of transmission** overall - The primary route remains **fecal-oral**, especially in settings with contaminated food or water - Sexual transmission typically involves fecal-oral exposure during sexual practices

Hospital-acquired infections US Medical PG Question 7: A regional academic medical center has 10 cases of adenovirus in the span of a week among its ICU patients. A committee is formed to investigate this outbreak. They are tasked with identifying the patients and interviewing the care providers to understand how adenovirus could have been spread from patient to patient. This committee will review charts, talk to the care provider teams, and investigate current patient safety and sanitation measures in the ICU. The goal of the committee is to identify weaknesses in the current system and to put in place a plan to help prevent this sort of outbreak from reoccurring in the future. The committee is most likely using what type of analysis?

• A. Simulation
• B. Root cause analysis (Correct Answer)
• C. Algorithmic analysis
• D. Heuristic analysis
• E. Failure mode and effects analysis

Hospital-acquired infections Explanation: ***Root cause analysis*** - The committee's goal is to **identify weaknesses** in the current system and **prevent recurrence**, which aligns perfectly with the principles of **root cause analysis (RCA)**. - RCA is a structured method for **identifying the underlying causes** of problems or incidents, rather than just addressing symptoms. *Simulation* - **Simulation** involves creating a model of a process or system to test different scenarios and predict outcomes. - While useful for planning, it's not the primary method for investigating an actual past event or identifying causative factors after an outbreak has occurred. *Algorithmic analysis* - **Algorithmic analysis** is primarily used in computer science to evaluate the efficiency and complexity of algorithms. - It does not apply to investigating the spread of infectious diseases or healthcare system failures. *Heuristic analysis* - **Heuristic analysis** involves using a rule of thumb or an educated guess to solve a problem quickly and efficiently, especially when perfect solutions are not feasible. - This approach is less systematic and comprehensive than what is required to thoroughly investigate an outbreak and identify root causes. *Failure mode and effects analysis* - **Failure mode and effects analysis (FMEA)** is a proactive method used to identify **potential failure modes** in a system and their effects *before* an event occurs. - The committee is investigating an **already existing problem**, making RCA more appropriate than FMEA, which is used for risk assessment of future processes.

Hospital-acquired infections US Medical PG Question 8: A 65-year-old man is admitted to the hospital because of a 1-month history of fatigue, intermittent fever, and weakness. Results from a peripheral blood smear taken during his evaluation are indicative of possible acute myeloid leukemia. Bone marrow aspiration and subsequent cytogenetic studies confirm the diagnosis. The physician sets aside an appointed time-slot and arranges a meeting in a quiet office to inform him about the diagnosis and discuss his options. He has been encouraged to bring someone along to the appointment if he wanted. He comes to your office at the appointed time with his daughter. He appears relaxed, with a full range of affect. Which of the following is the most appropriate opening statement in this situation?

• A. Your lab reports show that you have an acute myeloid leukemia
• B. What is your understanding of the reasons we did bone marrow aspiration and cytogenetic studies? (Correct Answer)
• C. You must be curious and maybe even anxious about the results of your tests.
• D. I may need to refer you to a blood cancer specialist because of your diagnosis. You may need chemotherapy or radiotherapy, which we are not equipped for.
• E. Would you like to know all the details of your diagnosis, or would you prefer I just explain to you what our options are?

Hospital-acquired infections Explanation: ***"What is your understanding of the reasons we did bone marrow aspiration and cytogenetic studies?"*** - This **open-ended question** allows the patient to express their current knowledge and perceptions, which helps the physician tailor the discussion. - It establishes a **patient-centered approach**, respecting the patient's existing understanding and preparing them for further information. *"You must be curious and maybe even anxious about the results of your tests."* - While empathic, this statement makes an **assumption about the patient's feelings** rather than inviting them to share their own. - It is often better to ask directly or use more open-ended questions that allow the patient to express their true emotions, especially given their **relaxed demeanor**. *"I may need to refer you to a blood cancer specialist because of your diagnosis. You may need chemotherapy or radiotherapy, which we are not equipped for.”"* - This statement immediately introduces **overwhelming and potentially alarming information** (referral, chemotherapy, radiotherapy) without first establishing the diagnosis or assessing the patient's readiness to receive it. - It prematurely jumps to treatment and logistics, potentially causing **unnecessary distress** before the patient has processed the core diagnosis. *"Would you like to know all the details of your diagnosis, or would you prefer I just explain to you what our options are?""* - While it attempts to assess the patient's preference for information, this question is a **closed-ended "either/or" choice** that might limit the patient's ability to express nuanced needs. - It also prematurely introduces the idea of "options" without first explaining the diagnosis in an understandable context. *"Your lab reports show that you have an acute myeloid leukemia"* - This is a **direct and blunt delivery of a serious diagnosis** without any preparatory context or assessment of the patient's existing knowledge or emotional state. - Delivering such news abruptly can be shocking and overwhelming, potentially **hindering effective communication** and rapport building.

Hospital-acquired infections US Medical PG Question 9: A 13-year-old boy is brought to the emergency department because of vomiting, diarrhea, abdominal pain, and dizziness for the past 3 hours with fever, chills, and muscle pain for the last day. He had presented 5 days ago for an episode of epistaxis caused by nasal picking and was treated with placement of anterior nasal packing. His parents report that the bleeding stopped, but they forgot to remove the nasal pack. His temperature is 40.0°C (104.0°F), pulse is 124/min, respirations are 28/min, and blood pressure is 96/68 mm Hg. He looks confused, and physical exam shows conjunctival and oropharyngeal hyperemia with a diffuse, erythematous, macular rash over the body that involves the palms and the soles. Removal of the anterior nasal pack shows hyperemia with purulent discharge from the underlying mucosa. Laboratory studies show: Total white blood cell count 30,000/mm3 (30 x 109/L) Differential count Neutrophils 90% Lymphocytes 8% Monocytes 1% Eosinophils 1% Basophils 0% Platelet count 95,000/mm3 (95 x 109/L) Serum creatine phosphokinase 400 IU/L What is the most likely diagnosis for this patient?

• A. Stevens-Johnson syndrome
• B. Measles
• C. Disseminated gonococcal infection
• D. Herpes simplex virus type 2 (HSV-2) meningitis
• E. Toxic shock syndrome (Correct Answer)

Hospital-acquired infections Explanation: ***Toxic shock syndrome*** - The patient's presentation with **fever**, **hypotension**, **diffuse erythematous rash** involving palms/soles, **multisystem involvement** (vomiting, diarrhea, dizziness, confusion, elevated CPK), and the history of prolonged **nasal packing** (a common nidus for *Staphylococcus aureus* toxin production) is highly characteristic of **toxic shock syndrome (TSS)**. - **Leukocytosis with neutrophilia** and **thrombocytopenia** are also common laboratory findings in TSS. *Stevens-Johnson syndrome* - Characterized by **mucocutaneous lesions** with epidermal detachment, forming **bullae** and **erosions**, often preceded by fever and flu-like symptoms. - While it can involve mucous membranes, the **diffuse erythematous macular rash without bullae** and the rapid development of **shock** are not typical features. *Measles* - Presents with a **maculopapular rash** that typically starts on the face and spreads downwards, often coalescing. It is preceded by **prodromal symptoms** like cough, coryza, conjunctivitis, and **Koplik spots**. - **Hypotension**, **severe multiorgan dysfunction**, and **nasal packing as a risk factor** are not features of measles. *Disseminated gonococcal infection* - Can cause **fever**, migratory **polyarthralgia**, and a **pustular or vesiculopustular rash** with hemorrhagic lesions, primarily on the extremities. - The described **diffuse erythematous macular rash**, severe hypotension, and history of nasal packing do not fit the typical presentation of disseminated gonococcal infection. *Herpes simplex virus type 2 (HSV-2) meningitis* - Primarily causes **aseptic meningitis** with symptoms like fever, headache, stiff neck, and photophobia. - It does not explain the **diffuse erythematous rash**, **hypotension**, **multisystem involvement**, or the role of **nasal packing** in the patient's presentation.

Hospital-acquired infections US Medical PG Question 10: An 83-year-old male presents to the emergency department with altered mental status. The patient’s vitals signs are as follows: temperature is 100.7 deg F (38.2 deg C), blood pressure is 143/68 mmHg, heart rate is 102/min, and respirations are 22/min. The caretaker states that the patient is usually incontinent of urine, but she has not seen any soiled adult diapers in the past 48 hours. A foley catheter is placed with immediate return of a large volume of cloudy, pink urine. Which of the following correctly explains the expected findings from this patient’s dipstick urinalysis?

• A. Detection of an enzyme produced by white blood cells
• B. Detection of urinary nitrate conversion by gram-negative pathogens (Correct Answer)
• C. Detection of an enzyme produced by red blood cells
• D. Detection of urinary nitrate conversion by gram-positive pathogens
• E. Direct detection of white blood cell surface proteins

Hospital-acquired infections Explanation: ***Detection of urinary nitrate conversion by gram-negative pathogens*** - The presence of **nitrites** on a urine dipstick is a highly specific indicator of a **urinary tract infection (UTI)** caused by **gram-negative bacteria**. - **Gram-negative bacteria** like *E. coli* possess an enzyme, **nitrate reductase**, which converts urinary nitrates (normally present from dietary intake) into nitrites. - This is the **most specific finding** for gram-negative UTI and directly explains the expected dipstick result in this patient with cloudy urine and clinical signs of infection. *Detection of an enzyme produced by white blood cells* - This refers to the detection of **leukocyte esterase**, an enzyme released by neutrophils (white blood cells) in response to infection or inflammation. - While **leukocyte esterase** would likely be positive in this case of UTI, it is **less specific** than nitrite detection because it can be positive in any inflammatory condition of the urinary tract, not just bacterial infections. - The **nitrite test** is more specific for identifying **gram-negative bacterial** infections, which are the most common cause of UTIs. *Detection of an enzyme produced by red blood cells* - This refers to the detection of **hemoglobin**, which can be indirectly detected by dipstick due to its peroxidase-like activity. While the patient has **pink urine** (indicating hematuria), this finding is less specific for a **bacterial UTI** than nitrites and does not explain the *cause* of the infection. - Hematuria can be caused by various factors, including irritation from infection, kidney stones, trauma, or malignancy, and doesn't directly point to the type of pathogen. *Detection of urinary nitrate conversion by gram-positive pathogens* - **Gram-positive pathogens**, such as *Staphylococcus saprophyticus* or *Enterococcus faecalis*, which can cause UTIs, typically **do not convert urinary nitrates to nitrites** because they lack nitrate reductase enzyme. - Therefore, a positive nitrite test generally rules out a gram-positive infection as the sole cause of the positive dipstick finding. *Direct detection of white blood cell surface proteins* - The dipstick test for **leukocytes** (white blood cells) detects **leukocyte esterase**, an enzyme *released by* neutrophils, not their surface proteins directly. - While **leukocyte esterase** would likely be positive in this case, a positive **nitrite** test is more specific to the type of bacterial infection (gram-negative) responsible for the majority of UTIs.

Hospital-acquired infections Flashcard 1 of 2

Question: What is the route of transmission of influenza?_____

Answer: Respiratory droplets

Hospital-acquired infections Flashcard 2 of 2

Question: Klebsiella, enterobacter, and serratia commonly exhibit multi-drug _____

Answer: resistance