What is the most likely organism causing symptoms in an elderly male with fever, cough, and shortness of breath (SOB) for 3 days, with an air bronchogram sign on chest X-ray, severe anemia (low hemoglobin), and high reticulocyte count?

Most Likely Organism: Streptococcus pneumoniae

In an elderly male presenting with acute pneumonia (fever, cough, shortness of breath for 3 days) and air bronchogram on chest X-ray, Streptococcus pneumoniae is the most common causative organism, regardless of the presence of severe anemia with high reticulocyte count. 1, 2, 3, 4

Rationale for Streptococcus pneumoniae

Epidemiologic Evidence

• S. pneumoniae is the most common bacterial pathogen in community-acquired pneumonia (CAP) across all clinical settings, accounting for the majority of cases in outpatients, hospitalized patients, and even ICU admissions 1, 2, 4
• In elderly patients specifically, S. pneumoniae remains the predominant organism, present in up to one-third of all hospitalized CAP patients 1
• Multiple guideline sources consistently identify S. pneumoniae as the leading cause of acute bacterial pneumonia with acute onset of productive cough and short duration of illness (<3 days) 1

Radiographic Correlation

• Air bronchogram is a highly specific radiographic finding for bacterial pneumonia, particularly pneumococcal pneumonia 5
• The presence of air bronchograms within consolidation has 96% specificity for pneumonia and is characteristic of lobar consolidation patterns typical of S. pneumoniae 5
• The acute bacterial pneumonia pattern described (acute onset, productive cough, <3 days illness) with air bronchogram strongly suggests S. pneumoniae over atypical organisms 1

Clinical Presentation Match

• The 3-day duration with acute onset of fever, cough, and dyspnea fits the classic presentation of acute bacterial pneumonia rather than atypical pneumonia 1
• Atypical organisms like Mycoplasma pneumoniae typically present with minimal sputum production for ≥3 days, not the acute presentation described here 1

Why Not Mycoplasma pneumoniae

Clinical Pattern Mismatch

• Mycoplasma pneumoniae causes atypical pneumonia characterized by cough with minimal sputum production, gradual onset, and typically longer duration before presentation 1
• The acute 3-day presentation with presumed productive symptoms is inconsistent with Mycoplasma's typical course 1

Radiographic Findings

• Mycoplasma typically produces diffuse, non-segmental ground-glass opacities or interstitial patterns, not the focal air bronchogram pattern described 5
• Air bronchograms are characteristic of alveolar consolidation from bacterial pathogens, not atypical organisms 5

Epidemiologic Frequency

• While Mycoplasma is recognized as a cause of CAP, it occurs far less frequently than S. pneumoniae in elderly patients 1
• In hospitalized patients, S. pneumoniae is consistently more common than Mycoplasma across all age groups 1

Addressing the Hematologic Findings

Anemia and Reticulocytosis Context

• The severe anemia (Hg 6.8) with high reticulocyte count suggests hemolytic anemia, which can occur with severe pneumococcal infection 3
• Pneumococcal pneumonia is associated with significant systemic complications including hematologic abnormalities 3
• This hematologic picture does not change the most likely organism—S. pneumoniae remains the answer—but may indicate severe disease with complications 3

Clinical Pitfall to Avoid

• Do not be distracted by the anemia findings; they represent a complication or concurrent process, not a clue toward an atypical organism 3
• The core clinical presentation (acute onset, air bronchogram, elderly patient) overwhelmingly points to S. pneumoniae 1, 2, 4

Answer: B. Streptococcus pneumoniae

The combination of elderly age, acute presentation (<3 days), air bronchogram on chest X-ray, and the epidemiologic dominance of S. pneumoniae in CAP makes this the correct answer. 1, 2, 3, 4