Hospital-Acquired Pneumonia

Hospital-acquired pneumonia (HAP) is a new infection of the lung parenchyma that develops more than 48 hours after hospital admission. Epidemiologic data suggest that HAP occurs in up to 1.6% of patients, prolongs hospital stay by 2 to 3 days, and represents the most common hospital-acquired infection leading to death in critically ill patients. The morbidity and mortality attributed to HAP are significantly increased if the infection is caused by multidrug-resistant pathogens. The subset of HAP occurring more than 48 hours after initiation of mechanical ventilation is termed ventilator-associated pneumonia (VAP). The concept of a healthcare-associated pneumonia (HCAP), referring to a pneumonia diagnosed outside of the acute care setting, was purposefully removed from the 2016 Infectious Disease Society of American (IDSA)/American Thoracic Society (ATS) guidelines as more recent evidence suggested HCAP pathogens more closely resemble those seen in community-acquired pneumonia than those seen in HAP. Risk factors for HAP/VAP are diverse and include both patient-specific and treatment-associated elements. The diagnostic criteria for HAP/VAP require a new infiltrate on chest radiography in conjunction with typical clinical and laboratory findings of pneumonia. Although microbiologic confirmation is ideal, the optimal diagnostic strategy is debated. Recent trends in the microbial resistance rates for pathogens causing HAP/VAP have led to significant changes in the recommendations for empirical therapy, with an increased reliance on patient-specific factors and local antimicrobial resistance patterns. Limited new antibiotic development and high attributable mortality rates highlight the importance of evidence-based HAP/VAP prevention strategies.

A 72-year-old-man with a history of chronic obstructive pulmonary disease (COPD) sought attention for progressive shortness of breath and wheezing. Two days before presentation, the patient developed subjective fevers, chills, and myalgias. The following morning, his chronic cough had significantly worsened and he was producing more phlegm than usual. By the afternoon, he developed progressive shortness of breath with wheezing that would not respond to his rescue inhalers. His wife called the paramedics, and he was brought into the emergency department.

On exam, the patient had a temperature of 38.4°C, respiratory rate of 32, blood pressure of 147/86 and an oxygen saturation of 86% on 6 L/min of supplemental oxygen. He was dyspneic and unable to speak in full sentences with notable diaphoresis. His pulmonary examination revealed use of accessory muscles with minimal air movement and diffuse expiratory wheezing. The patient was urgently intubated and transferred to the medical intensive care unit (ICU). His complete blood count (CBC) showed a white blood cell count (WBC) of 11,000/mm ³ , and his chest radiograph showed hyperexpanded lungs with no focal consolidations, pleural effusions, or pneumothorax. A respiratory viral panel revealed infection with influenza A and the patient was treated for both his viral infection and a COPD exacerbation with azithromycin, methylprednisone, bronchodilators, and oseltamivir. The patient subsequently defervesced, and his oxygen requirements became minimal.

Five days later the patient developed a new fever and had an increase in his respiratory rate and oxygen requirements. A CBC revealed an increase in his WBC, and a repeat chest radiograph showed a new right lower lobe consolidation. The patient was diagnosed with a VAP and had a tracheal aspirate sent for Gram stain and culture. He was started on empiric broad-spectrum antibiotics, and 2 days later his cultures returned positive for methicillin-resistant Staphylococcus aureus (MRSA). His antibiotics were narrowed to vancomycin monotherapy, and he was successfully extubated 2 days later.

Patients with COPD are prone to developing respiratory failure when exposed to respiratory viruses, such as influenza. This patient’s age and underlying lung disease increased his predilection to develop a VAP, which is a known complication of endotracheal intubation with mechanical ventilation. His severity of illness merited initiation of antimicrobial therapy that covered MRSA, which is a common postinfluenza superinfection.