A 29-year-old man comes to the physician for a routine health maintenance examination. He feels well. He works as a nurse at a local hospital in the city. Three days ago, he had a needlestick injury from a patient whose serology is positive for hepatitis B. He completed the 3-dose regimen of the hepatitis B vaccine 2 years ago. His other immunizations are up-to-date. He appears healthy. Physical examination shows no abnormalities. He is concerned about his risk of being infected with hepatitis B following his needlestick injury. Serum studies show negative results for hepatitis B surface antigen, hepatitis B surface antibody, and hepatitis C antibody. Which of the following is the most appropriate next step in management?

Administer hepatitis B immunoglobulin and 3-dose regimen of hepatitis B vaccine

Revaccinate with 3-dose regimen of hepatitis B vaccine

Revaccinate with two doses of hepatitis B vaccine

Administer hepatitis B immunoglobulin

Administer hepatitis B immunoglobulin and single dose hepatitis B vaccine

A 28-year-old soldier is brought back to a military treatment facility 45 minutes after sustaining injuries in a building fire from a mortar attack. He was trapped inside the building for around 20 minutes. On arrival, he is confused and appears uncomfortable. He has a Glasgow Coma Score of 13. His pulse is 113/min, respirations are 18/min, and blood pressure is 108/70 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Examination shows multiple second-degree burns over the chest and bilateral upper extremities and third-degree burns over the face. There are black sediments seen within the nose and mouth. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. The abdomen is soft and nontender. Intravenous fluid resuscitation is begun. Which of the following is the most appropriate next step in management?

Intubation and mechanical ventilation

Insertion of nasogastric tube and enteral nutrition

Intravenous corticosteroid therapy

A 36-year-old man comes to the physician because of a 2-week history of productive cough, weight loss, and intermittent fever. He recently returned from a 6-month medical deployment to Indonesia. He appears tired. Physical examination shows nontender, enlarged, palpable cervical lymph nodes. An x-ray of the chest shows right-sided hilar lymphadenopathy. A sputum smear shows acid-fast bacilli. A diagnosis of pulmonary tuberculosis is made from PCR testing of the sputum. The patient requests that the physician does not inform anyone of this diagnosis because he is worried about losing his job. Which of the following is the most appropriate initial action by the physician?

Inform the local public health department of the diagnosis

Request the patient's permission to discuss the diagnosis with an infectious disease specialist

Assure the patient that his diagnosis will remain confidential

Confirm the diagnosis with a sputum culture

Notify all of the patient's household contacts of the diagnosis

A 67-year-old man is brought to the emergency department because of severe dyspnea and orthopnea for 6 hours. He has a history of congestive heart disease and an ejection fraction of 40%. The medical history is otherwise unremarkable. He appears confused. At the hospital, his blood pressure is 165/110 mm Hg, the pulse is 135/min, the respirations are 48/min, and the temperature is 36.2°C (97.2°F). Crackles are heard at both lung bases. There is pitting edema from the midtibia to the ankle bilaterally. The patient is intubated and admitted to the critical care unit for mechanical ventilation and treatment. Intravenous morphine, diuretics, and nitroglycerine are initiated. Which of the following is the most effective method to prevent nosocomial infection in this patient?

Daily oropharynx decontamination with antiseptic agent

Daily urinary catheter irrigation with antimicrobial agent

A 35-year-old man is brought into the emergency department by emergency medical services with his right hand wrapped in bloody bandages. The patient states that he is a carpenter and was cutting some wood for a home renovation project when he looked away and injured one of his digits with a circular table saw. He states that his index finger was sliced off and is being brought in by his wife. On exam, his vitals are within normal limits and stable, and he is missing part of his second digit on his right hand distal to the proximal interphalangeal joint. How should the digit be transported to the hospital for the best outcome?

In a sterile plastic bag wrapped in saline moistened gauze on ice

In the pocket of a coat or a jacket

In a sterile plastic bag wrapped in saline moistened gauze

A 70-year-old woman comes to the physician for the evaluation of loss of urine for the last several months. She loses small amounts of urine without warning after coughing or sneezing. She also sometimes forgets the names of her relatives. She is retired and lives at an assisted-living facility. She has type 2 diabetes mellitus and hypertension. Her older sister recently received a ventriculoperitoneal shunt. She does not smoke or drink alcohol. Medications include metformin and enalapril. Vital signs are within normal limits. She walks without any problems. Sensation to pinprick and light touch is normal. Which of the following is the most likely underlying cause of this patient's symptoms?

Decreased cerebrospinal fluid absorption

Bacterial infection of the urinary tract

Infection control practices for USMLE Step 2 CK: High-Yield Microbiology Lessons

Standard & Contact Precautions - The First Line of Defense

Standard Precautions: The universal baseline applied to ALL patients, assuming everyone is potentially infectious.
- Hand Hygiene: Before and after every patient contact.
- PPE: Use of gloves, gowns, and eye protection based on anticipated exposure to blood or body fluids.
Contact Precautions: For pathogens spread by direct/indirect contact. Includes Standard Precautions plus:
- Private Room: Or cohorting with a patient with the same active infection.
- Gown & Gloves: Required for all entries into the patient room.
- Key Pathogens: MRSA, VRE, C. difficile, Scabies, RSV.

⭐ For Clostridioides difficile, hand hygiene MUST be performed with soap and water. Alcohol-based hand rubs are ineffective against C. diff spores.

Droplet & Airborne Precautions - Guarding the Air

Essential for preventing nosocomial spread of respiratory pathogens. The distinction hinges on particle size, which dictates aerosolization and travel distance.

Feature	Droplet Precautions	Airborne Precautions
Particle Size	Large respiratory droplets (>5 µm)	Small droplet nuclei (<5 µm)
Transmission	Travel short distances (~3-6 ft)	Suspended in air; travel long distances
Room Type	Private room preferred; cohorting possible	Airborne Infection Isolation Room (AIIR); negative pressure, ≥12 air changes/hr
PPE	Surgical mask within 3 ft of patient	N95 respirator or PAPR required before entry
Pathogens	📌 SPIDERMAN: Strep, Pertussis, Influenza, Diphtheria, Epiglottitis, Rubella, Meningitis	📌 MTV: Measles (Rubeola), TB (pulmonary/laryngeal), Varicella (chickenpox/disseminated zoster)

⭐ For airborne precautions, the door to the patient's room must remain closed. Patients leaving the AIIR should wear a surgical mask to contain respiratory secretions.

Disinfection & Sterilization - The Decontamination Spectrum

Decontamination: A process to make an object safe to handle.
Spectrum of Activity: Effectiveness varies based on the microbial load and type.

Resistance to Disinfectants (Most to Least):
- Prions
- Bacterial spores (e.g., Clostridium, Bacillus)
- Mycobacteria
- Nonenveloped viruses
- Fungi
- Vegetative bacteria
- Enveloped viruses

⭐ Prions are highly resistant to standard sterilization. Decontamination requires treatment with 1 N NaOH or concentrated bleach followed by autoclaving at 134°C for at least 1 hour.

Post-Exposure Prophylaxis - The Needlestick Protocol

Immediate Steps: Wash with soap and water. Report the incident immediately.
Assess Source: Test source patient for HBsAg, anti-HCV, and anti-HIV antibodies.
Baseline Labs: Draw blood from exposed person for baseline testing.
HBV Prophylaxis: For non-immune individuals, administer HBIG and initiate the HBV vaccine series.
HCV Prophylaxis: No PEP exists. Monitor with HCV RNA testing.
HIV Prophylaxis: Initiate a 3-drug antiretroviral therapy (ART) regimen. Start within 2 hours and no later than 72 hours post-exposure for 4 weeks.

⭐ The efficacy of HIV PEP is highest when initiated immediately. A preferred modern regimen is Tenofovir + Emtricitabine + Raltegravir.

High‑Yield Points - ⚡ Biggest Takeaways

Hand hygiene is the single most effective measure to prevent HAIs; use soap and water for spore-forming organisms like C. difficile.

Use Contact Precautions (gown and gloves) for pathogens like MRSA and VRE.

Employ Droplet Precautions (surgical mask) for infections such as influenza and Neisseria meningitidis.

Airborne Precautions (N95 respirator, negative pressure room) are crucial for tuberculosis, measles, and varicella.

Minimize device-related infections by ensuring aseptic technique and removing catheters/lines promptly.

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