Pneumonia is defined as an infection of the parenchyma of the lung [1]. As reported by the National Center for Health Statistics in 2014, pneumonia is the eighth cause of mortality in the US [2]. Pneumonia is classified into two groups: community acquired pneumonia (CAP) and hospital acquired pneumonia (HAP). The CAP affects approximately 5.6 million patients every year, and it is ranked as the sixth cause of death in people older than 65 years old [3]. Pneumonia has a bimodal distribution, significantly affecting the very young (< 5 years old) and the elderly (> 65 years old) [4]. The etiological agents of CAPs are most commonly: Streptococcus pneumoniae, Mycoplasma pneumoniae and respiratory syncytial virus, while in other cross-sectional study showed most CAP did not recover an etiological agent in 56.7% (Figure 1) [5][6].

Methicillin resistant Staphylococcus aureus (MRSA), a rare pathogen, its incidence has increased over the last years and nowadays has been identified as a potential pathogen in 8.9% of CAP cases [7]. The MRSA pneumonia is often a post-viral pneumonia, acting as a secondary bacterial infection that commonly affects the lower respiratory tract after a primary viral infection [8]. The MRSA pneumonia can be necrotizing to the lung parenchyma resulting in cavitation due to the pore-forming cytotoxin called Panton–Valentine leukocidin (PVL). This cytotoxin induces cell death by rapid disruption of mitochondrial homeostasis via the activation of caspases (3 and 9) resulting in the lysis of the polymorphonuclear leukocytes and lung cells [9]. This type of pneumonic process usually presents with severe symptoms requiring inpatient management. The most commonly prescribed antibiotics for MRSA pneumonia are vancomycin and linezolid. Vancomycin should be avoided in acute kidney injury and bacterial cultures with minimum inhibitory concentration (MIC) >2. Linezolid is advantageous in MRSA pneumonia as it markedly suppresses PVL protein expression, hindering the progression of the cavitation [10]. The presence of bone marrow (such as thrombocytopenia) problems can impede the implementation of linezolid therapy. Another type of anti-MRSA antibiotic, daptomycin, should not be prescribed in patients with pneumonia because it is inhibited by pulmonary surfactant [11]. Ceftaroline fosamil, a fifth-generation cephalosporin, which has a broad-spectrum activity against gram positive bacteria, working in the penicillin binding protein, that is approved for the treatment CAP’s and skin and soft tissue infection caused by MRSA, but its use for the treatment of MRSA pneumonia has not been approved yet.

A case of 72-year old Hispanic male presented with a medical history of hypertension, diabetes mellitus type 2, chronic kidney disease stage 3B, unspecified chronic thrombocytopenia and asthma that developed an upper respiratory tract infection that manifested with fever and rhinorrhea and resolved without treatment. Ten days later, the patient arrived at the emergency room due to productive cough of rust colored sputum that started three days before admission. Associated symptoms included malaise, fever, chills and shortness of breath. Triage vital signs showed: blood pressure 149/84 mmHg, heart rate 89 beats per minute, respiratory rate 24/minute, temperature 38.8°C, Sat 89% (room air).

Physical examination was remarkable for an acutely ill patient with non-toxic appearance in mild distress that was talking in words. Trachea was midline, thorax showed symmetric expansion and respiratory system was remarkable for bilateral inspiratory and expiratory crackles, and dullness to percussion was noted at the left lower lobe.

Laboratory studies: White blood cells 26.43x10⁹/uL, hemoglobin 9.4 g/dl, hematocrit 27.8%, platelets 74x10⁹/L, sodium 146 mmol/L, potassium 3.6 mmol/L, chloride 108.00 mmol/L, carbon dioxide 27.00 mmol/L, blood urea nitrogen 29 mg/dL, creatinine 1.7 mg/dL, glomerular filtration rate by Cockcroft–Gault 34.2 mL/min, BUN/CREA ratio 17.1.

Arterial blood gasses: pH 7.381, pCO₂ 44.9 mmHg, pO₂ 61 mmHg, HCO₃ 25.8 mmol/L, O₂ sat 86%, expected A-a gradient 22.0 mmHg, calculated A-a gradient 32.6 mmHg, PaO₂/FiO₂ 290.5 mmHg.

Chest X-ray taken at the emergency room showed perihilar thickening, left costophrenic angle effacement and left lower lobe consolidation (Figure 2). Findings were worrisome for abscess formation, therefore, chest CT scan was performed immediately and showed bilateral pulmonary nodules, including several cavitary nodules, in addition to patchy bilateral lower lung airspace disease and small left pleural effusion (Figure 3). CURB-65 and PORT/PSI were calculated showing and found to be: 2 and class IV, respectively (Table 1), (Table 2) [12]. The patient was admitted to medicine ward with diagnosis of CAP and was initially managed with azithromycin/ceftriaxone. Skin tuberculin test was performed and was determined to be 0 mm. However, persistent fever and tachypnea for 72 hours resulted in the need for reassessment. The follow-up chest X-ray showed worsening of the previous infiltrates/cavities and a second chest CT scan was ordered (Figure 4) and (Figure 5). Sputum culture revealed MRSA with a MIC >2 for vancomycin, thus requiring alternative treatment. Infectious disease services were consulted on the use of linezolid, but linezolid use was discouraged due to increased risk of thrombocytopenia. Infectious disease instead recommended the use of ceftaroline fosamil with renal adjustment at 400 mg intravenous every 12 hours as monotherapy. The patient received ceftaroline fosamil as ordered by the infectious disease service and became afebrile within the next 36 hours, completing 21 days of antibiotic. Lung masses were biopsied by interventional radiology and were determined to be negative for malignancy. The patient was discharged home without supplemental oxygen and was followed at the outpatient clinic the next week and monthly for two months and remained afebrile with no shortness of breath.

Our patient was admitted with diagnosis of CAP and was initially managed with azithromycin/ceftriaxone, a regimen that covers most common pathogens. The current history of upper respiratory symptoms had resolved, and MRSA pneumonia was not initially considered, primarily because of a lack of a bilateral pattern on chest X-ray. However, the patient’s chest X-ray findings were not related to a specific etiologic agent [13]. After 72 hours of antibiotic treatment, the patient’s persistent fever warranted a reassessment of the medical treatment. Although X-rays are no pathognomonic for a specific pathogen, new imaging studies showed suspicious findings of MRSA necrotizing pneumonia and the suspicion was confirmed with sputum culture [14]. An anti-MRSA drug should be prescribed but vancomycin was not recommended due to high MIC (>2) and linezolid was discouraged in view of thrombocytopenia. ID service recommended ceftaroline fosamil, a fifth-generation cephalosporin with spectrum that cover MRSA. Our patient received ceftaroline fosamil 400 mg IV every 12 hour for 21 days as monotherapy with a great outcome, finally being discharge home with no supplemental oxygen. The follow-up chest X-ray was requested for two months later in view of delayed imaging clearance due to Staphylococcus aureus pneumonia (Table 3) [15].

With each diagnosis of CAP, the physician must inquire about any recent history of upper respiratory symptoms that occurred in the last 8–14 days. Antibiotic regimens should not be based solely on imaging studies but also correlate with the past medical history. Ceftaroline fosamil, a fifth-generation cephalosporin that works in the PBP (penicillin binding protein), is approved for CAP and skin and soft tissue infection and is characterized by its coverage against MRSA. However, it is not FDA approved for MRSA-CAP. When common anti-MRSA pneumonia antibiotics, such as vancomycin and linezolid, are contraindicated due to MIC >2 or additional comorbidities, as in the case of our patient, ceftaroline fosamil could be considered. This novel antibiotic poses the benefit that need modification only in renal impairment, does not need modification in liver disease including Child-Pugh B or B and finally does not need to be followed with peaks or trough. Our patient was managed with an anti-MRSA cephalosporin for 21 days as a salvage therapy with a positive outcome. The authors suggest that a large multicenter clinical trial can be performed to assess the efficacy of this drug in treating MRSA-CAPs.

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