Personal ViewRethinking the concepts of community-acquired and health-care-associated pneumonia
Introduction
The 2005 update of the American Thoracic Society and Infectious Diseases Society of America (ATS/IDSA) guidelines on nosocomial pneumonia1 introduced the new term health-care-associated pneumonia (HCAP). On the basis of data published at the same time as the guidelines, a population with frequent or chronic contact with health care was found to be at risk of multidrug-resistant pathogens frequently not covered in empirical initial antimicrobial treatment recommended in guidelines for the management of community-acquired pneumonia. Mortality was around 20%, twice as high as that in patients with community-acquired pneumonia and almost as high as that in non-ventilated patients with nosocomial pneumonia.2 The recommendation of the guidelines was to treat patients classified as having HCAP intensively with a combination of broad-spectrum antimicrobial drugs, which is similar to recommended treatment for patients at risk of multidrug-resistant pneumonia.1
Since the publication of the 2005 guidelines, nine studies have provided original data on HCAP,2, 3, 4, 5, 6, 7, 8, 9, 10 one of these studies is an abstract,10 and only two were prospective.6, 10 However, 14 published reviews11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 suggest widespread acceptance of HCAP. In view of the worldwide threat of increasing resistance to antimicrobial drugs, acceptance of HCAP without good evidence would increase the use of antimicrobial drugs and produce selection pressure for drug-resistant organisms. Therefore, a critical review of available data to put the clinical problems underlying HCAP into perspective is needed.
Until recently, the basic classification of pneumonia was as the triad of community-acquired pneumonia, hospital-acquired pneumonia, and pneumonia in immunosuppressed patients. Table 1 lists the core elements of the definition of these types of pneumonia. These types of pneumonia are not solely a textbook classification but also a clinical concept. The classification incorporates two principal notions: first, host immunity (and the types of immunosuppression) and environment of pneumonia acquisition are associated with a predictable microbial spectrum; and, second, empirical initial antimicrobial treatment can rely on a predictable microbial spectrum.
Although the triad was clearly a simplification with uncertainties at the edges of these definitions (and the need to take into account severity, local epidemiology, and particular risk factors), the concept worked in clinical practice: it allowed clinicians to be confident when making important clinical decisions.
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Challenges to the concept of community-acquired pneumonia
The first challenge to the concept of community acquired pneumonia was the emergence of the new entity, so-called community-acquired pneumonia in the elderly, in view of the increasing number of elderly patients with pneumonia.25, 26, 27, 28, 29, 30, 31, 32, 33 Disease in elderly patients seemed to differ in microbial spectrum. However, there were conflicting results. In general, studies from the USA had an increased incidence of Gram-negative Enterobacteriaceae (and, in part, Pseudomonas
HCAP—the reference data
Data supporting the concept of HCAP were derived from a retrospective 2-year (2002–03) cohort analysis in 59 US hospitals in 4543 non-immunosuppressed patients with pneumonia (table 3).2 Microbiological data were culture results from the first 5 days after admission to hospital. The analysis resulted in three main messages: HCAP was frequent (988 patients; 21·9%); many patients had Enterobacteriaceae and multidrug-resistant pathogens (ie, 26·5% meticillin-resistant Staphylococcus aureus [MRSA],
Validation studies outside the USA
Three studies outside the USA have attempted to validate the concept of HCAP: two in southern Europe6, 7 and one in Japan.8 In a prospective study of epidemiology, antimicrobial treatment, and outcome in Barcelona, Spain,6 727 patients admitted to hospital with pneumonia were included, of whom 17·3% met the criteria of HCAP (table 3). Overall, patients with HCAP were older, had greater comorbidity, and more severe pneumonia at presentation than those with community-acquired pneumonia as
Attempts to refine the concept
According to the concept of HCAP, the presence of more drug-resistant pathogens implies less adequate initial empirical antimicrobial treatment, resulting in excess mortality. Therefore, more aggressive diagnostic and therapeutic approaches, including broader initial empirical antimicrobial treatment, are recommended to reduce mortality. However, validation studies do not support this concept. No consistent pattern of drug-resistance exists in HCAP, and inadequate empirical antimicrobial
A misconception to be revised
The concept of HCAP has the merit of including a population under-recognised in guidelines so far—ie, patients who are elderly or severely disabled with repeated or chronic contact with health care, leading to a risk of infection with drug-resistant pathogens. However, as defined at present, the concept has contributed to significant confusion, creating the risk of overtreatment.
Definitions of HCAP are highly diverse (table 3), in part uninterpretable, and deleterious for any useful
Where to go from here
The most obvious change in pneumonia epidemiology is the increasing number of patients who are elderly or severely disabled, have chronic contacts with health care, and are residents of nursing homes: all such patients have a raised risk of infection with drug-resistant pathogens. This change reflects demographic developments and increases in life expectancy. A nationwide quality assurance programme in Germany53 included all adults with community-acquired pneumonia admitted to hospital during 2
Towards a new concept of community-acquired pneumonia
All criteria used to define HCAP can be plausibly integrated in the classical triad pneumonia classification system (figure 1).
However, approaches to community-acquired pneumonia in patients admitted to hospital need to change to address concerns about drug-resistant pathogens (panel and figure 2). Patients with community-acquired pneumonia aged 65 years or older are the core group in view of higher incidence, specific microbial patterns and risk factors for drug-resistant pathogens, and
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