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What Should We Make of Candida Isolated from Respiratory Tract Samples?
Abstract & Commentary
By Andrew M. Luks, MD, Pulmonary and Critical Care Medicine, University of Washington, Seattle, is Associate Editor for Critical Care Alert.
Dr. Luks reports no financial relationship to this field of study.
Synopsis: This prospective study of autopsies performed on patients who died in a medical ICU demonstrates that candida pneumonia is a very rare occurrence and suggests that antifungal therapy can be safely withheld in patients in whom Candida species are isolated from the respiratory tract during a fever work-up.
Source: Meersseman W, et al. Significance of the isolation of Candida species from airway samples in critically ill patients: A prospective, autopsy study. Intensive Care Med 2009 Apr 9; Epub ahead of print.
Colonization of the respiratory tract and other sites with Candida species is common in ICU patients but it is unclear how often these species cause pneumonia that warrants antifungal therapy. Meersseman and colleagues sought to clarify this issue by defining the incidence of candida pneumonia and the value of isolating Candida species from respiratory tract samples in immunocompetent and immunosuppressed individuals with evidence of pneumonia at the time of autopsy.
They conducted a prospective study of all autopsies performed on patients who died in the medical ICU over a 2-year period at a single institution. A variety of data was collected on all deceased patients including, but not limited to, Candida species isolated from tracheal aspirates or bronchoalveolar lavage (BAL) specimens, identification of Candida species from other sites ≤ 14 days before death, and antifungal treatment. Tracheal surveillance cultures were performed routinely on a weekly basis at this institution as well as in response to suspicion for pneumonia, while BAL was performed to evaluate new pulmonary opacities in immunocompromised patients. All autopsies were performed within 24 hours of death. Histologic criteria for the diagnosis of acute candida pneumonia included the presence of neutrophils in the interstitium and alveolar spaces and microscopic evidence of fungal organisms with histologic features typical for Candida spp. (i.e., budding yeast and pseudohyphae). Cultures were not performed on the post-mortem specimens.
During the study period 1587 patients were admitted to the ICU and 301 (19%) died. Autopsies were performed on 232 patients (77% autopsy rate), 135 (58%) of whom had histologic evidence of pneumonia. Of the patients with histologic evidence of pneumonia, 77 had growth of Candida species on respiratory tract samples (56 positive tracheal aspirates, 12 positive BAL samples, and 9 with growth on both) while 58 had no positive cultures for the organism. Both groups included patients on corticosteroids or with neutropenia while the group of patients with histologic evidence of pneumonia also included 21 patients with either solid or hematologic malignancy or who had undergone solid organ transplant. Histologic evidence of candida pneumonia was not found in any of the autopsied patients. An additional 47 of the autopsied patients had growth of Candida species on respiratory tract samples but no evidence of pneumonia of any etiology on autopsy. Eleven patients across all study groups had candidemia, while 3 had candida peritonitis and 4 patients had candiduria. None of the patients with candida cultured from sites outside the respiratory tract developed candida pneumonia.
Fever is a common problem in ICU patients for which we invest considerable time and resources in attempts to identify an etiology. On many occasions, cultures fail to show a definitive explanation for the fever but do provide evidence of Candida species on either a BAL or tracheal aspirate. As the fevers continue this leaves many clinicians wondering whether it is worth treating the patient with antifungal therapy for a possible candida pneumonia. In fact, even though current guidelines recommend against the use of antifungal therapy when Candida species are isolated in BAL fluid in immunocompetent patients, 24% of ICU physicians report prescribing antifungal agents under these circumstances.1
The study by Meersseman and colleagues provides useful information that should guide decisions in this situation and prevent the unnecessary use of antifungal therapy. Consistent with the results of prior studies that have examined this issue,2 they found no evidence of candida pneumonia in a mixed population of ICU patients. Although data were collected at only a single center and the autopsy specimens were not cultured, there was a very high autopsy rate and, as a result, the chances of missing cases where candida pneumonia was present but was not detected because histologic examination could not be performed were limited.
Another strong aspect of the study was the fact that the study population included a wide array of medical ICU patients, including immunocompetent patients and those with various forms of immunosuppression such as corticosteroid use, neutropenia, organ transplantation, and solid and hematologic malignancies. While the results should be applied in the care of immunocompetent patients, we should still be cautious before applying them to all immunosuppressed patients, as the total number of such patients in the study was small and other studies have showed evidence of candida pneumonia in patients with malignancy or neutropenia.3 More studies involving other centers and larger sample sizes are necessary before we can disregard the possibility of candida pneumonia in immunosuppressed patients.
Finally, another situation in which clinicians broach the idea of antifungal therapy is when Candida species are cultured concurrently from multiple sites such as the urine and respiratory tract. Eighteen patients in this study, however, had positive cultures from other sites including the blood, urine, or peritoneum, yet candida pneumonia was not subsequently identified in any of these patients. While not definitive given the low numbers of patients in this situation, this finding does suggest that antifungal therapy for pneumonia can be withheld when candida is concurrently identified in urine and respiratory tract samples and should be reserved for patients with blood stream infections or peritonitis.