HIGH INCIDENCE OF FALSE‐POSITIVE ASPERGILLUS GALACTOMANNAN TEST RESULTS IN PATIENTS WITH ASPIRATION PNEUMONIA

Abstract

Letter to the Editor: The Platelia Aspergillus assay for detecting circulating galactomannan (GM) has been widely used for diagnosing invasive aspergillosis, but a major difficulty with this enzyme-linked immunosorbent assay (ELISA) is the transient false-positive results that occur with the administration of some beta-lactam antibiotics or with intestinal translocation of lipoteichoic acid of Bifidobacterial species origin in neonates and infants.1, 2 In the present study, an unexpectedly high rate of false-positive Aspergillus GM test results was found in patients with definite aspiration pneumonia. It has been reported that GM is contained in various beverages and foods, such as tea, milk, pasta, rice, and pepper,3 and several reports have suggested that silent aspiration is an important factor in the pathogenesis of community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP) in elderly people.4, 5 In this context, it was hypothesized that GM of food origin reaches the blood circulation through the inflamed respiratory tract mucosa in patients with aspiration pneumonia and causes ELISA reactivity. The study population consisted of 40 patients with pulmonary infection who were admitted to Kumamoto Saishunso National Hospital from April 2007 to March 2008, including 29 patients with definite aspiration pneumonia according to the guidelines of the Japanese Respiratory Society6 and 11 patients with CAP or lower respiratory tract infection without aspiration as controls (7 patients with pneumonia and 4 patients with acute bronchitis). All control patients were younger than 65 and had neither dysphagia nor central nervous system diseases. A serum sample was examined for the presence of GM in each patient with the use of the Platelia Aspergillus kit (Bio-Rad, Marnes-La-Coquette, France).2, 7 The records of these patients were retrospectively reviewed for the diagnosis of invasive aspergillosis, and no patient fulfilled the criteria of the European Organization for Research and Treatment of Cancer-Mycoses Study Group.7 Plateria Aspergillus test results were considered false positives when the GM index was 0.5 or greater and 5.0 or less in the serum without a diagnosis of proven, probable, or possible invasive aspergillosis.2, 7 None of the patients were given the antibiotics that are known to cause false-positive Platelia Aspergillus test results, such as piperacillin-tazobactam, amoxicillin-clavulanic acid, and amoxicillin, before the test was performed.1-3 As shown in Figure 1, 27 of 29 patients with definite aspiration pneumonia showed false-positive results (n=29; mean age±standard deviation=80.8±15.7; 16 men, 13 women). Alternatively, all control patients except one had a negative Platelia Aspergillus test result (n=11; mean age=52.1±14.6; 5 men, 6 women) (Fisher exact probability test, P<.001). The serum GM index was significantly higher in patients with aspiration pneumonia (median 0.8, range 0.1–5.0) than in patients with pneumonia or acute bronchitis without aspiration (median 0.3, range 0.1–0.5) (Mann-Whitney U-test, P<.001). Galactomannan (GM) index values in patients with aspiration pneumonia and patients with pneumonia or acute bronchitis without aspiration. A GM index of ≥0.5 and ≤5.0 was considered a false-positive result. Its retrospective nature and small sample size limit this report, although the preliminary data suggest that the circulating GM in patients with aspiration pneumonia originates from beverages and foods aspirated into the lower respiratory tract. In conclusion, the use of serum GM antigen measurement may be helpful for diagnosing aspiration pneumonia due to silent aspiration in elderly patients with CAP or HAP. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this letter. Author Contributions: Yusuke Tomita, Mineharu Sugimoto, Osamu Kawano: study concept and design, acquisition of subjects and data, analysis. Yusuke Tomita, Mineharu Sugimoto, Hirotugu Kohrogi: interpretation of data and preparation of manuscript. Sponsor's Role: None.