The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

AN INDEPENDENT ANALYSIS OF POSSIBLE PATIENT RALSTONIA COLONIZATION AND INFECTION BY VAPOTHERM

Wesley M. Granger, PhD, RRT, Jonathan B. Waugh PhD, RRT

University of Alabama at Birmingham, Birmingham, Alabama

Introduction: An independent analysis was conducted using data submitted to Vapotherm, Inc., as part of an investigation regarding a recent FDA Preliminary Public Health Notification concerning reported Ralstonia cultured from a respiratory gas administration device at several hospitals. The purpose of this analysis was to investigate the possible relationship between Vapotherm use and the reported patient colonization and infection with Ralstonia.

Methods:
We were allowed independent access on a consultant basis to the data reported on Ralstonia cultures to the company. We performed an analysis of reported positive Ralstonia cultures from patients and a possible connection to Vapotherm device use.

Results:
The reports indicate that 35 of 38 patients with positive cultures were exposed to Vapotherm. Based on MDR our analysis reveals that only 5.8% of the positive patient cultures received Vapotherm as the only respiratory therapy modality. Most of the patients had been intubated and on mechanical ventilation before being placed on Vapotherm therapy. Further analysis reveals that 1 patient was a Cystic Fibrosis patient who may have had pre-existing infection not related to Vapotherm therapy. A 2005 multi-center analysis of Ralstonia in cystic fibrosis patients indicated that 46% of the Ralstonia colonizations and infections were by R. mannitolilytica (JCM 43(7):3463-3466). A recent CDC analysis using cluster analysis statistics identified the "Outbreak Species" as Ralstonia mannitolilytica and stated that "strains from 10 states were highly related" based on pulsed-field gel electrophoresis (PFGE). The CDC defines this as similarity values of 77% or higher. Other published studies indicate that similarities are not significant unless they show 90% or greater values and then only indicate that they are the same strain and not necessarily are from a common contamination source. Our analysis of the banding patterns showed strains from only 5 states with a > 90% pattern similarity by cluster analysis as reported by the CDC.  Other outbreak analyses in the literature using PFGE techniques on common source contaminations show identical banding patterns and not just similar patterns.

Discussion:
A study in 2005 (AEM 71(8):4690-4694) has questioned the use of cluster analysis in evaluating banding patterns because cluster analysis tends to show artificially high levels of similarity even between strains that should not be very similar. They suggest the use of discriminant function analysis as a more appropriate statistical analysis of similarities. As a result of this information it is very difficult to determine if the identified organisms are from a common source and therefore may not be directly linked to Vapotherm therapy.

Conclusions:
(1). Less than 6% of the Ralstonia cultures reported as positive were in patients who had received only Vapotherm therapy. (2). Few if any of the reported 8 infections could be directly related to the use of Vapotherm. (3). The result of the analysis using PFGE does not show a common source of colonization by Ralstonia mannitolilytica but only proves that these are all the same, most common, species that might be expected in hospitals where cystic fibrosis patients are treated.

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