Editorial Commentary: The Mismatch Between Physicians' Expectations and Microbiologic Reality

pneumonia, antimicrobials, microbiology

(See the Major Article by Jones et al on pages 1403–10.)

In 2005, a joint committee of the American Thoracic Society and the Infectious Diseases Society of America presented a clinical practice guideline that created a new “type” of pneumonia: healthcare-associated pneumonia (HCAP) [1]. The committee recognized that there were reports of patients presenting from the community with bacterial pathogens that are more typically nosocomial, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant (MDR) Pseudomonas aeruginosa. These guidelines recommended the use of broad-spectrum antibiotic coverage for patients with risk factors for these potential MDR bacterial pathogens. Risk factors identified included prior antibiotics, recent hospitalization, skilled nursing home residence, dialysis, home wound care, or family members with MDR pathogens.

In 2015, these guidelines are increasing controversial for several reasons. First, the risk factors identified by these guidelines for MDR pathogens have little supporting evidence, and recent studies have not identified risk factors that appropriately identify those with potentially MDR pathogens or completely exclude those with only typical community-acquired pneumonia (CAP) pathogens [2]. Second, most population-based studies have demonstrated low rates of outpatient-acquired pneumonia due to potentially MDR bacterial pathogens, and these rates have been relatively stable during the past 10 years [3–5].

Finally, most studies of broad-spectrum antibiotic therapy for patients with HCAP risk factors have not shown a survival benefit for such therapy compared with CAP guideline–concordant antibiotic therapy [2]. Why? Most likely because patients with HCAP risk factors have many more comorbid conditions than patients with “typical” CAP and are more significantly ill at presentation, independent of the microbiologic cause of pneumonia. Moreover, patients thought to have HCAP frequently do not receive either an antipneumococcal fluoroquinolone and/or macrolide, such as azithromycin. Studies have demonstrated that patients with CAP who receive antimicrobial regimens with either antipneumococcal fluoroquinolones or macrolides have significantly lower mortality rates than those who do not [6, 7]. Because of these issues, the HCAP recommendations are currently being reconsidered.

In this issue of Clinical Infectious Diseases, Jones et al [8] present important findings on pneumonia due to potentially MDR bacterial pathogens, using data from the nationwide Department of Veterans Affairs (VA) healthcare System. They examined over 95 000 hospitalizations over a 5-year period and found that during this time period there were no significant increases in pneumonia due to either Pseudomonas or Acinetobacter infections while MRSA infections actually decreased. Overall <5% of cultures identified a potentially MDR pathogen. Even though there was no increase in the percentage of pneumonias due to such pathogens, the empiric use of vancomycin more than doubled (to 31%), and the use of piperacillin-tazobactam increased by 70%. These increases were at the expense of macrolide therapy, primarily with azithromycin, which has been demonstrated to be associated with significantly lower pneumonia-related mortality [9]. Finally, there was little indication that physicians were able to identify patients who were at risk for pneumonia due to potential MDR pathogens and therefore should have appropriately received broad-spectrum antibiotic therapy.

Although well done, the study by Jones et al [8] does have several limitations. The most important is that the VA system is not necessarily representative of the rest of the US healthcare system. However, given the prevalence of comorbid conditions in VA patients, one would expect rates of potential MDR pathogens in that system to be at least as high as in most other healthcare systems. In addition, as with any observational study, it is unclear how many potentially MDR pathogens were missed during routine clinical care because appropriate cultures were not obtained or inappropriate collection techniques were used. However, these limitations should not dampen our appreciation for this study, which adds important information to the discussion regarding HCAP.

The findings reported by Jones et al [8] reinforce the fact that research is critically needed to develop reliable methods for identifying those truly at risk for pneumonia due to MDR pathogens. They also demonstrate why every hospital needs to study its own microbiologic data to identify the most common organisms for patients with outpatient-acquired pneumonia and the antibiotic resistance patterns in that hospital's patient population. Although some hospitals do have clinically important numbers of patients with outpatient-acquired pneumonia due to MRSA or MDR P. aeruginosa, it is now clear that these institutions are the exception, not the rule.

Research is also critically needed to determine the appropriate empiric antibiotic regimens to improve survival rates in these patients. Although there remains some controversy regarding the potential benefits of macrolide antibiotics in patients with CAP, it is concerning that most studies of HCAP still demonstrate that typical community-acquired pathogens (eg, Streptococcus pneumoniae) are most common organisms and that the recommended empiric HCAP antibiotic regimens, with few exceptions, have been associated with higher mortality rates than empiric antibiotic regimens that are concordant with CAP guidelines.

In conclusion, the study by Jones et al [8] demonstrated low rates of potential MDR pathogens, soaring rates of broad-spectrum antibiotic use, and the clear inability of practicing clinicians to identify patients at risk for pneumonia caused by potentially MDR pathogens. The clear message for researchers is that we need well-designed studies of methods to identify patients with potential MDR pathogens and the most appropriate empiric antibiotic treatments. For clinicians, the message is less clear. Each hospital needs to routinely look at its microbiologic data and, after discussion with all stakeholders, determine which patients should be treated with broad-spectrum antibiotics versus CAP-guideline concordant therapy that is concordant with CAP guidelines. Without these discussions, we will be facing even larger problems due to MDR infections in the future.

Notes

Financial support. This material is the result of work supported with resources and the use of facilities at the VA North Texas Health Care System, which had no role in the preparation, review, or approval of the manuscript.

Potential conflict of interest. Author certifies no potential conflicts of interest.

The author has submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.