pulmonary disorders
Hospital Acquired Pneumonia
Etiology of Hospital Acquired Pneumonia
The most common cause of hospital-acquired pneumonia is microaspiration of bacteria that colonize the oropharynx and upper airways in seriously ill patients. Seeding of the lung due to bacteremia or inhalation of contaminated aerosols (ie, airborne particles containingLegionellaspecies,Aspergillusspecies, or influenza virus) are less common causes. Risk factors for hospital-acquired pneumonia include previous antibiotic treatment, high gastric pH (due to stress ulcer prophylaxis or therapy with H2 blockers or proton pump inhibitors), and coexisting cardiac, pulmonary, hepatic, or renal insufficiency. Major risk factors for postoperative pneumonia are Age>70 Abdominal or thoracic surgery Functional debilitation Pathogens and antibiotic resistance patterns vary significantly among institutions and can vary within institutions over short periods (eg, month to month). Local antibiograms at the institutional level that are updated on a regular basis are essential in determination of appropriate empiric antibiotic therapy. In general, the most important pathogens are Enteric gram-negative bacilli, especiallyPseudomonas aeruginosa Gram-positive cocci, especially methicillin-sensitiveStaphylococcus aureusand methicillin-resistantS. aureus(MRSA) Other important enteric gram-negative bacteria includeEnterobacterspecies,Klebsiella pneumoniae,Escherichia coli,Serratia marcescens,Proteusspecies, andAcinetobacterspecies. Methicillin-sensitiveS. aureus,Streptococcus pneumoniae, andHaemophilus influenzaeare most commonly implicated when pneumonia develops within 4 to 7 days of hospitalization, whereasP. aeruginosa, MRSA, and enteric gram-negative organisms become more common with increasing duration of hospitalization. Risk factors for infection with multidrug resistant (MDR) pathogens include prior intravenous antibiotic treatment (within the previous 90 days), structural lung disease, colonization with MDR pathogens, and high rates of prevalence of these pathogens in the local hospital environment ( Etiology reference ). Infection with a resistant organism markedly worsens mortality and morbidity. infections. Chronic suppurative lung diseases such as Cystic Fibrosis and There is increasing recognition of viruses as a cause of HAP in immunocompetent patients and of viruses and fungi in immunocompromised patients. 1.Kalil AC, Metersky ML, Klompas M, et al: Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society.Clin Infect Dis63(5):e61–111, 2016. 