The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

THE ASSOCIATION OF MECHANICAL VENTILATION AND RALSTONIA COLONIZATION/INFECTION IN THE USA BY META-ANALYSIS

Jonathan B. Waugh, PhD, RRT, RPFT; Amit Gaggar, MD; Wesley Granger, PhD, RRT. University of Alabama at Birmingham, Birmingham, AL.

Introduction: A recent FDA Preliminary Public Health Notification reported Ralstonia spp. had been cultured from a respiratory gas administration device at several hospitals (first reported October 2005 in CDC Morbidity and Mortality Weekly Report).1 Ralstonia species are gram-negative bacilli that are commonly found in the environment but rarely reported in the hospital setting. Ralstonia strains have traditionally exhibited low virulence in humans.1 We performed a secondary analysis of published clinical reports of Ralstonia to determine if being on mechanical ventilation (MV) had an influence on how many colonizations converted to infection (symptomatic).

Methods:
We performed a meta-analysis of published multiple incidences of Ralstonia cultured in patients with respiratory infections in the USA (through July 2005). The treatment group was patients on MV and the control group consisted of patients not on MV. We developed two different analyses; one for colonization with Ralstonia and the other for infection with Ralstonia.

Results:


Colonization with Ralstonia:

Study Name Odds Ratio 95% Lower CI 95% Upper CI Percent Weight
MMWR 1983 34.48 2.09 586.04 8.73
MMWR 1998 10.32 4.23 25.22 87.80
Burns et al 125.25 1.30 11219.63 3.47
Average 12.51 5.41 28.8805 100.00

Infection with Ralstonia:

Study Name Odds Ratio 95% Lower CI 95% Upper CI Percent Weight
MMWR 1983 1.00 0.020 50.89 24.03
Timm et al 1.49 0.029 76.82 23.96
Labraca et al 72.67 4.36 1211.39 33.26
Burns et al 201.00 1.65 24543.34 18.75
Average 12.38 0.96 159.05 100.00

The wide 95% confidence intervals are due to the fact that these studies have small numbers. The overall average from combining all the studies is the statistic of interest.

Conclusions:
1. Patients on MV have a 12.5 times increased chance of becoming colonized with Ralstonia. 2. Since the overall average 95% CI for infection had an odds ratio which crosses one, there is not enough evidence to conclude an increased rate of infection with MV. 3. Respiratory infection due to known positive cultures of Ralstonia in the USA was rare enough to make comparative analysis difficult (11 cases out of a total of 632 patients or 1.74%). That rate may be biased by reporting only positive cultures during periods of a Ralstonia outbreak. That, plus the use of small control groups relative to a much larger clinical cohort, indicates a small clinical impact of Ralstonia colonizations for mechanically ventilated patients.

REFERENCE: 1. MMWR 2005:54(41);1052-1053.

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