A 65-year-old woman is brought to the emergency department by her daughter for fever and cough. She just returned from a cruise trip to the Bahamas with her family 5 days ago and reports that she has been feeling ill since then. She endorses fever, productive cough, and general malaise. Her daughter also mentions that the patient has been having some diarrhea but reports that the rest of her family has been experiencing similar symptoms. Physical examination was significant for localized crackles at the right lower lobe. Laboratory findings are as follows: Serum Na+: 130 mEq/L K+: 3.9 mEq/L Cl-: 98 mEq/L HCO3-: 27 mEq/L Mg2+: 1.8 mEq/L What findings would you expect in this patient?

High titers of cold agglutinins

Gram-negative rod on chocolate agar with factors V and X

Gram-positive diplococci on Gram stain

Broad-based budding on fungal sputum culture

A patient is hospitalized for pneumonia. Gram-positive cocci in clusters are seen on sputum gram stain. Which of the following clinical scenarios is most commonly associated with this form of pneumonia?

Hospitalized adult with development of pneumonia symptoms 2 weeks following a viral illness

Elderly patient who has trouble swallowing and poor dentition

An alcoholic with evidence of empyema and "currant jelly sputum"

An otherwise healthy young adult with a week of mild fatigue, chills, and cough

HIV positive adult with a CD4 count less than 150 and an impaired diffusion capacity

A 59-year-old man comes to the clinic for an annual well-exam. He was lost to follow-up for the past 3 years due to marital issues but reports that he feels fine. The patient reports, “I feel tired but it is probably because I am getting old. I do feel a little feverish today - I think I got a cold.” His past medical history is significant for hypertension that is controlled with hydrochlorothiazide. He reports fatigue, congestion, cough, and night sweats. He denies any sick contacts, recent travel, weight changes, chest pain, or dizziness. His temperature is 101°F (38.3°C), blood pressure is 151/98 mmHg, pulse is 97/min, and respirations are 15/min. His laboratory values are shown below: Hemoglobin: 13.5 g/dL Hematocrit: 41% Leukocyte count: 25,000/mm^3 Segmented neutrophils: 73% Bands: 8% Eosinophils: 1% Basophils: 2% Lymphocytes: 15% Monocytes: 2% Platelet count: 200,000/mm^3 What diagnostic test would be helpful in distinguishing this patient’s condition from pneumonia?

Magnetic resonance imaging of the chest

A 59-year-old woman comes to the emergency department because of a 2-day history of worsening fever, chills, malaise, productive cough, and difficulty breathing. Three days ago, she returned from a trip to South Africa. She has type 2 diabetes mellitus, hypertension, and varicose veins. Her current medications include metformin, lisinopril, and atorvastatin. Her temperature is 39.4°C (102.9°F), pulse is 102/minute, blood pressure is 94/68 mm Hg, and respirations are 31/minute. Pulse oximetry on 2 L of oxygen via nasal cannula shows an oxygen saturation of 91%. Examination reveals decreased breath sounds and dull percussion over the left lung base. The skin is very warm and well-perfused. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 11.6 g/dL Leukocyte count 15,400/mm3 platelet count 282,000/mm3 Serum Na+ 144 mEq/L Cl- 104 mEq/L K+ 4.9 mEq/L Creatinine 1.5 mg/dL Blood and urine for cultures are obtained. Intravenous fluid resuscitation is begun. Which of the following is the next best step in management?

Intravenous ceftriaxone and azithromycin

External cooling and intravenous acetaminophen

Intravenous vancomycin and ceftriaxone

A 24-year-old woman, otherwise healthy, presents with a non-productive cough, sore throat, and myalgia. The patient reports that her symptoms started gradually 2 weeks ago and have not improved. She has no significant past medical history and no current medications. She is a college student and denies any recent overseas travel. The patient received the flu vaccine this year, and her 2-part PPD required for school was negative. She does not smoke, drink, or use recreational drugs. The patient denies being sexually active. The vital signs include: temperature 37.0°C (98.6°F), blood pressure 110/75 mm Hg, pulse 98/min, respirations 20/min, and oxygen saturation 99% on room air. On physical exam, the patient is alert and cooperative. The cardiac exam is normal. There are rales present bilaterally over both lung fields. The skin and conjunctiva are pale. The laboratory tests are pending. The chest X-ray is shown in the image. Which of the following laboratory findings would also commonly be found in this patient?

Elevated cold agglutinin titers

Heinz bodies on peripheral smear

Low serum ferritin and serum iron

Schistocytes on peripheral smear

Pneumonia (community-acquired, hospital-acquired) for USMLE Step 2 CK: High-Yield Internal Medicine Lessons

Pneumonia Types - Lungs Under Siege

Community-Acquired (CAP): Acquired outside a hospital or within 48 hours of admission.
Hospital-Acquired (HAP): Develops ≥48 hours after hospital admission.
- Ventilator-Associated (VAP): Arises >48 hours after endotracheal intubation.

Chest X-ray patterns in pneumonia

Clinical Syndromes:
- Typical: Sudden onset, high fever, purulent cough, lobar consolidation. Caused by typical organisms (S. pneumoniae).
- Atypical ("Walking"): Insidious onset, low-grade fever, non-productive cough, patchy infiltrates. Caused by atypical organisms (Mycoplasma, Chlamydia, Legionella).

⭐ Exam Favorite: Legionella pneumophila, an atypical cause, is classically associated with GI symptoms (diarrhea) and hyponatremia (low sodium).

Etiology - The Usual Suspects

Pneumonia Type	Common Pathogens
CAP (Outpatient)	S. pneumoniae, Mycoplasma, H. influenzae, Viruses
CAP (Inpatient)	S. pneumoniae, H. influenzae, S. aureus, Legionella
HAP / VAP	Pseudomonas, S. aureus (MRSA), GNRs (Klebsiella, E. coli)

-   **Alcoholism:** *Klebsiella pneumoniae* (currant jelly sputum)
-   **COPD/Smoking:** *H. influenzae*, *Pseudomonas*
-   **Post-Influenza:** *S. aureus* (often MRSA)
-   **Aspiration:** Oral anaerobes (e.g., *Peptostreptococcus*)

⭐ Pseudomonas aeruginosa is a critical pathogen in patients with structural lung diseases like cystic fibrosis or bronchiectasis, often requiring specific antibiotic coverage.

📌 Atypicals: 'My Legion of Clamoring Q-Ts' (Mycoplasma, Legionella, Chlamydophila, Coxiella)

Diagnosis & Severity - Spotting the Shadow

Clinical & Radiologic Dx:
- H&P: Fever, cough, dyspnea, crackles on auscultation.
- Chest X-ray: Key to diagnosis. Look for:
  - Lobar consolidation: Classic for S. pneumoniae.
  - Interstitial infiltrates: Atypical pathogens (e.g., Mycoplasma).
  - Cavities: S. aureus, anaerobes, TB.
- Labs: ↑ WBC; ↑ Procalcitonin suggests bacterial etiology.
Severity Scoring (CURB-65 for CAP):
- Confusion (new onset)
- Uremia (BUN > 20 mg/dL)
- Respiratory Rate (≥ 30 breaths/min)
- Blood Pressure (SBP < 90 or DBP ≤ 60 mmHg)
- Age (≥ 65 years)
- Disposition: 0-1 (Outpatient), 2 (Inpatient), ≥3 (ICU).

⭐ Procalcitonin is a specific marker for bacterial infections; levels >0.25 ng/mL strongly support bacterial pneumonia and guide antibiotic stewardship.

Treatment - The Antibiotic Arsenal

Community-Acquired Pneumonia (CAP): Empiric choice depends on severity.
Hospital-Acquired (HAP) / Ventilator-Associated (VAP): Cover MRSA & Pseudomonas.
- MRSA: Vancomycin or Linezolid.
- Anti-pseudomonal: Piperacillin-tazobactam, Cefepime, or a Carbapenem.

⭐ For CAP, empiric outpatient therapy must cover atypical pathogens. Standard beta-lactams alone are insufficient against Mycoplasma, Chlamydia, and Legionella.

High‑Yield Points - ⚡ Biggest Takeaways

S. pneumoniae is the most common cause of Community-Acquired Pneumonia (CAP).

Atypical pathogens like Mycoplasma cause "walking pneumonia," especially in young adults.

Use the CURB-65 score to determine CAP severity and need for hospitalization.

Hospital-Acquired Pneumonia (HAP) develops >48 hours post-admission; common culprits are Pseudomonas and MRSA.

Legionella is linked to contaminated water and classically causes hyponatremia and GI symptoms.

For severe pneumonia, obtain blood and sputum cultures before starting antibiotics.

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