Reasons for Deterioration or Nonresolution

There are several possible causes of rapid deterioration or failure to improve. These include the possibility that the process being treated is not pneumonia or that certain host, bacterial, and therapeutic factors have not been considered.

Many noninfectious processes may be mistaken for HAP, including atelectasis, congestive heart failure, pulmonary embolus with infarction, lung contusion, and chemical pneumonitis after aspiration (Wunderink et al. 1992).

Host factors associated with a failure to improve during empiric therapy include the presence of any condition that is known to increase mortality, e.g., prolonged mechanical ventilation, respiratory failure, an underlying fatal condition, age greater than 60 years, bilateral radiographic infiltrates, prior antibiotic therapy, prior pneumonia, and/or chronic lung disease (Torres et al. 1990, Luna and Niederman 2002).

Bacterial variables can also be associated with an adverse outcome of initial therapy. The infecting pathogen can be resistant at the outset to the chosen antibiotic or can acquire resistance during therapy, particularly P. aeruginosa treated with a single agent (Fink et al. 1994). Certain types of infection are associated with a poor outcome, especially those with Gram-negative bacilli, polymicrobial flora, or bacteria that have acquired antibiotic resistance (Fagon etal. 1993,

Luna et al. 1999). In patients who are mechanically ventilated, superinfection with P. aeruginosa or Acinetobacter spp. has a particularly high mortality. Finally, pneumonia can be due to other pathogens (i.e., Mycobacterium tuberculosis, fungi, or respiratory viruses) or an unusual bacterial pathogen not included in the initial empiric regimen. In addition, some patients can have clinically unrecognized immunosuppression and Pneumocystis jiroveci or Aspergillus spp. pneumonia may be a cause of nonresponse to therapy.

Certain complications during therapy can also lead to an apparent failure in response to therapy. Some patients with HAP or VAP can have other sources of fever simultaneously, particularly sinusitis, vascular catheter-related infection, pseudomembranous enterocolitis, or urinary tract infections (Meduri et al. 1994). Complications of the original pneumonia can also lead to failure, including development of lung abscess or empyema. Other possible causes of persistent fever or pulmonary infiltrates include drug fever, sepsis with multiple system organ failure, or pulmonary embolus with secondary infarction.

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