Health care-associated pneumonia and community-acquired pneumonia: A single-center experience

Micek ST, Kollef KE, Reichley RM, et al. Antimicrob Agents Chemother 2007;51:3568–3573.

Summary:

In the 2005 American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) guidelines for nosocomial pneumonia, healthcare-associated pneumonia (HCAP) was identified as a form of nosocomial pneumonia that is caused by potentially multidrug-resistant (MDR) pathogens such as Pseudomonas aeruginosa (PA) and methicillin-resistant Staphylococcus aureus (MRSA). There are few studies of the bacteriology of HCAP, leading to some disagreement over the frequency of nosocomial pathogens in this form of pneumonia and uncertainty regarding the prevalence of HCAP.

Micek et al., with Marin Kollef of the AIM faculty, conducted a retrospective study to evaluate the frequency, epidemiology and bacteriology of HCAP in 639 patients at a single hospital over a 3-year period (2003–2005). All patients included in the study had either community-acquired pneumonia (CAP) or HCAP in addition to a new radiographic infiltrate plus clinical findings of infection, and a positive culture from sputum, tracheal aspirate, or bronchoscopy or blood samples. HCAP was defined as pneumonia with at least one of the following:

• Admission from a nursing home or long-term care facility;
• Previous hospitalisation in the past 12 months;
• Outpatient haemodialysis or infusion therapy at a hospital-based clinic;
• Immune suppression (steroid therapy of at least 5 mg prednisone/day, HIV infection, transplant, or other cause of immunosuppression such as chemotherapy).

The investigators found that HCAP was more common than CAP (431 vs 208 patients, respectively) and that the majority of patients (93.3%) were defined as having HCAP because of recent hospitalisation, with 69% having been hospitalised in the past 90 days and only 28.1% being resident in a nursing home. Bacteraemia was present in 37.5% of CAP patients and 30.9% of HCAP patients. The most common pathogens overall were MRSA (24.6%), Streptococcus pneumoniae (20.3%), PA (18.8%) and methicillin-sensitive S. aureus (13.8%). MRSA was more common among patients with HCAP compared with CAP (30.6% vs 12.0%, respectively), as was PA (25.5% vs 4.8%, respectively), whereas S. pneumoniae and Haemophilus species were more common in patients with CAP.

There was a significantly higher mortality rate among patients with HCAP than among those with CAP (24.6% vs 9.1%, respectively; p<0.001) and the administration of inappropriate initial antibiotic therapy (defined as use in the first 24 hours of an agent that was not active against the identified pathogen) was more common in HCAP patients than in CAP patients (28.3% vs 13.0%, respectively; p<0.001). When patients received a CAP therapy regimen in the setting of HCAP, therapy was inappropriate 30.9% of the time. The organisms present in HCAP patients that were most often treated with inappropriate therapy were PA, MRSA and other non-fermenting Gram-negatives. In a multivariate analysis of mortality, the relevant risk factors were: mechanical ventilation (odds ratio [OR] = 5.05); bacteraemia (OR = 3.26); and inappropriate antibiotic therapy (OR = 2.19).

This study adds to the data set on HCAP, demonstrating a high frequency of MDR pathogens and the need for appropriate therapy. The findings support the concept that HCAP is associated with a higher mortality rate than CAP and that HCAP should not always be treated as CAP because this approach commonly leads to inappropriate therapy, which in turn is a risk factor for mortality. There are, however some limitations to the study and the findings do not corroborate those of a recent Spanish study (Carratala et al. Arch Intern Med 2007;167:1393–1399). Although the Spanish study also found both a higher frequency of inappropriate therapy and a higher rate of mortality in HCAP compared with CAP, mortality was much lower than in Micek’s study, as was the frequency of MDR pathogens in HCAP patients. There are several reasons for the disparate findings:

• The Micek study was retrospective whereas the Spanish study was prospective;
• The Micek study only included patients with positive cultures, thus limiting the types of patient enrolled;
• The Micek study included patients defined as HCAP primarily because of recent hospitalisation and not commonly because of admission from a long-term care facility. In the Spanish study, only 43.7% had recent hospitalisation, compared with 93.3% in the Micek study;
• Both studies were performed in different institutions.

Considering all the data available, we clearly need more information about HCAP and the optimal approach to its therapy. The HCAP population is heterogeneous and it is likely that there is variation among patients at different institutions who fit into this category. We will hopefully better understand these subpopulations in the future, and realise that there is no one simple approach to therapy, but rather a need for individualised therapy based on specific patient factors (Niederman MS, Brito V. Clin Chest Med 2007;28:751–771).

AIM core principles supported:

This study supports the AIM principles in the areas of patient outcomes, antibiotic choice and resistance. Specific principles demonstrated in this study include:

• Select the most appropriate antibiotic depending on the patient, risk factors, suspected infection and resistance.
  • Clearly, HCAP patients are different from CAP patients and often require different therapy, but as discussed, we still need to better understand the subpopulations of HCAP patients.
• It is important to start with the appropriate empiric antibiotic first in nosocomial infections.
  • The current study extends this principle to HCAP, which is not always a nosocomial infection.
• Know the unit’s resistance profile and choose antibiotics accordingly.
  • As discussed, each hospital is likely to have a different population of patients with HCAP and the approach in each hospital should reflect knowledge of the types of patient treated there

Learning points:

• HCAP is a form of pneumonia that is not exactly the same as either CAP or nosocomial pneumonia; however, as with all serious infections, timely and appropriate therapy is needed to assure the best outcome.
• Patients with HCAP are a heterogeneous group and each hospital needs to develop an approach to therapy. To do this, hospitals need to identify the types of patient being treated in each hospital and to develop an approach that minimises the chance of inappropriate therapy, and avoids excessive use of broad-spectrum therapy for patients who could be treated successfully with a regimen having a narrower spectrum.