In February 2005, the American Thoracic Society (ATS) and the Infectious Disease Society of America (IDSA) released their joint guidelines for the management of nosocomial pneumonia.1 This impressive document was an extensive revision of guidelines released in 1996.2 These revised guidelines were widely anticipated because during the intervening nine-year span two trends had evolved. First, academic interest in nosocomial pneumonias grew dramatically. This is best illustrated by the exponential growth in the rate of scholarly publications regarding nosocomial pneumonia. A simple PubMed search of “nosocomial pneumonia” shows a six-fold increase in the number of publications devoted to this topic during the time that elapsed between the two sets of guidelines. (See Figure 1, p. 28.) Second, antimicrobial susceptibility to antibiotic therapy rapidly worsened, with many facilities reporting routine resistance in their intensive care units.
Given the growth in related scholarly activity, the 2005 guidelines are both comprehensive and lengthy—some 28 pages in total. The authors meticulously reviewed the nosocomial pneumonia literature, dividing it into manageable and clinically relevant subtopics: epidemiology, pathogenesis, modifiable risk factors, diagnostic testing, diagnostic strategies, antibiotic treatment, and response to therapy. The obvious strengths of the guidelines include that they were written by a collection of authoritative experts representing collaboration between the ATS and the IDSA and that they result in a collection of practical, evidence-based recommendations.
One of the most significant aspects of these guidelines is that they defined a “new” entity: healthcare-associated pneumonia (HCAP). The authors recognize HCAP patients as a unique population because they are at increased risk of harboring resistant pathogens. As defined by the guidelines, HCAP patients include those admitted for more than 48 hours in the past 90 days, those who reside in a nursing home or receive home infusion therapy or wound care, those who are on chronic hemodialysis, or patients who have a family member with a multidrug-resistant pathogen. Although not explicitly stated by the guidelines, it’s worth noting that the recommendations provided were intended to apply only to hospitalized patients with pneumonia.
Looking at the ATS-IDSA definition of HCAP, it is clear that the largest subset of HCAP patients is nursing home residents with pneumonia. Although these patients have historically been treated with agents recommended in community-acquired pneumonia (CAP) guidelines, they more closely resemble hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) patients in terms of their comorbidities, the presence of catheters and lines, and their prior exposure to antibiotics. Because these patients live longer and have more comorbid disease their care has become increasingly complex, often involving frequent transfers to hospitals or providers’ offices. Not surprisingly, long-term-care facility residents have become a reservoir for multidrug-resistant pathogens.3,4 This patient population will become increasingly important; the number of geriatric Americans is projected to continue to grow for the next 20 years.
Because increased mortality in pneumonia is strongly linked to initially inappropriate antibiotic therapy, the guidelines recommend much broader antibiotic coverage for the newly defined HCAP population.5,6 In the recent past, these patients have been most frequently treated with a third-generation cephalosporin and macrolide combination or a respiratory fluoroquinolone as monotherapy. Given the risk of multidrug-resistant pathogens in HCAP, these regimens are deemed inadequate by the current guidelines, which recommend a combination of:
- An antipseudomonal cephalosporin, an antipseudomonal carbapenem, or a ß-lactam/ß-lactamase inhibitor combination; plus
- An antipseudomonal fluoroquinolone or an aminoglycoside; plus
- Vancomycin or linezolid. (See Table 1, above.)
Controversies Surrounding the Guidelines
Although the revised guidelines were generally greeted with enthusiasm, several authors quickly pointed out that the evidence base supporting HCAP has significant limitations.7-9 Most importantly, studies dealing specifically with HCAP as it is defined by the guidelines are lacking. A review of the ATS-IDSA guidelines’ references reveals that only seven publications deal specifically with HCAP, and all of these focus on nursing home-acquired pneumonia.10-16 Also note that these seven studies use widely discrepant definitions of pneumonia, have varying microbiologic criteria, and include varying numbers of hospitalized and non-hospitalized patients. In addition to these limitations, much of the epidemiology of HCAP pathogens has been extrapolated from diseases other than pneumonia.