Studies seek better assessment of risk for resistant pneumonia

Nov 22, 2011 (CIDRAP News) – Two new studies shed some light on risk factors for drug-resistant healthcare-associated pneumonia (HCAP), one suggesting which factors carry the most weight and the other showing that a simple clinical scoring method can help identify the patients at greatest risk.

Both reports address the need to reserve broad-spectrum antibiotics for the patients who need them the most. They were published online yesterday in Clinical Infectious Diseases, along with commentaries from other experts.

In the first study, researchers from Italy sought to evaluate different risk factors for multidrug-resistant (MDR) HCAP. The observational, prospective study included all patients from the community who were admitted to a Milan hospital between April 2008 and April 2010.

For each patient they recorded the risk factors for acquiring a drug-resistant pathogen, using guidelines from the American Thoracic Society and the Infectious Diseases Society of America. Microbiologic tests were conducted on sputum, urine, and blood samples, and pathogens were tested for antibiotic susceptibility. Patients were given empiric antibiotic treatment as soon as pneumonia was diagnosed in the emergency department.

For comparison, they divided the patients into two groups: those with and without risk factors for drug-resistant HCAP.

Of 935 patients who were diagnosed with pneumonia during the study period, 473 (51%) had at least one risk factor for acquiring MDR bacteria. Patients in the risk factor group were more likely to be admitted with more severe disease.

Streptococcus pneumoniae was the most common pathogen detected in both study groups, but patients in the risk-factor group were more likely to have MDR bacteria (6.1% vs 0.9%).

After adjustment for several other factors, the top two risk factors were hospitalization in the previous 90 days and residency in a nursing home or extended-care facility. The researchers also found that the two risk factors were associated with in-hospital mortality across the entire cohort. "The double impact of these 2 risk factors on both microbiological and clinical outcomes emphasizes their roles," they wrote.

For each patient, they computed a score for predicting the risk of infection with resistant bacteria, which ranged from 0 to 12.5. For patients who scored 0.5 or less on the scale, the prevalence of resistant bacteria was 8%, compared with 38% in patients who had scores of 3 or greater.

The authors concluded that the risk factor and scoring findings support individual evaluation of each patient to determine a targeted approach to antibiotic treatment.

Two experts who commented on the study said the findings confirm earlier observations. The authors are Dr Martin Kollef, a critical care specialist at Washington University School of Medicine, and Dr Scott Micek, with the department of pharmacy at Barnes-Jewish Hospital in St Louis.

Studies such as the Italian one provide healthcare workers with a strategy to help determine appropriate treatment while avoiding overuse of broad-spectrum antibiotics, Kollef and Micek wrote. "Implicit in such a strategy is that physicians should be aware of the risk factor profile of the patients they are treating as well as the local patterns of MDR infection," they said.

They added that a good understanding of the patient's risk factor profile is also required to balance optimal treatment for the patient with antibiotic resistance prevention goals in healthcare settings.

In the second study, a group of US-based critical care specialists compared the accuracy of two methods for identifying resistant HCAP: a previously identified risk assessment tool or the complete HCAP definition. Their retrospective analysis was based on an evaluation of adults admitted to a hospital through the emergency department between January and December 2010. Kollef and Micek are among the authors.

The risk score they tested, published in 2008, assigns points for various risk factors: recent hospitalization (4 points), admission from a nursing home (3), chronic hemodialysis (2), and critical illness (1). The definition of HCAP included several criteria such as hospitalization for at least 48 hours during the past 90 days.

The patient cohort included 977 patients, and resistant organisms were isolated from 46.7%. About three-quarters of the patients met at least 1 HCAP criteria. Though patients with and without resistant infections did not vary demographically, those who were infected with resistant organisms were more likely to be severely ill and require intensive care unit (ICU) admission.

Results showed that 91% of patients with resistant organisms met the HCAP definition, though so did 65.6% those who didn't have resistant infections.

When the researchers looked at how risk scores correlated with resistant infections, they found that the prevalence of resistant infections was 15% in people who had a score of 0 and rose to nearly 75% in people who had a score above 6.

Their analysis revealed that the risk score was more sensitive than the HCAP definition. They predicted that using the HCAP definition as the trigger for prescribing broad-spectrum antibiotics would have resulted in overtreatment in 35% of the population. However, using a risk factor of more than 0 as a trigger would have resulted in 24.3% receiving unnecessary prescriptions.

The authors concluded that the HCAP definition is useful for encouraging physicians to recognize the prevalence of resistant infections in the emergency department, but it's time to modify the approach with pneumonia patients.

"If clinicians fail to grasp the implications of overuse of broad-spectrum agents and do not embrace approaches that limit this problem, future clinicians will face even more difficult challenges in the care of these patients," they wrote.

In a related commentary, two experts from Catholic University of Rome, Dr Rita Murri and Dr Gennaro De Pascale, wrote that the limitationss of the current HCAP definition call for more restrictive risk-stratification approaches to ensure appropriate antibiotic therapy. They said the study helps overcome come of these limitations by moving more toward risk factors for multi-drug resistant pneumonia.

They added that validation of the score in a prospective study is strongly warranted, and suggested that future treatment guidelines take into account the limits of the HCAP definition.

Aliberti S, Di Pasquale M, Zanaboni AM, et al. Stratifying risk factors for multidrug-resistant pathogens in hospitalized patients coming from the community with pneumonia. Clin Infect Dis 2011 Nov 21:[Abstract]

Kollef MH, Micek ST. Patients hospitalized with pneumonia: determining the need for broad-spectrum antibiotic therapy (commentary). Clin Infect Dis 2011;Nov 21:[Extract]

Shorr AF, Zilberberg MD, Reichley R, et al. Validation of a clinical score for assessing the risk of resistant pathogens in patients with pneumonia presenting to the emergency department. Clin Infect Dis 2011 Nov 21:[Abstract]

Murri R, De Pascale G. The challenge of identifying resistant-organism pneumonia in the emergency department: still navigating on the Erie Canal? (commentary). Clin Infect Dis 2001;Nov 21:[Extract]

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