Stenotrophomonas maltophilia contamination of nebulizers used to deliver aerosolized therapy to inpatients with cystic fibrosis

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Abstract

There is circumstantial evidence that nebulizer equipment may be a source of Stenotrophomonas maltophilia for patients with cystic fibrosis. Eighty-nine inpatient nebulizers were examined for evidence of S. maltophilia contamination of which nine (10%) yielded 14 strains of the bacterium. Environmental samples were obtained from 73 different sites on the ward, of which 17 (23%) yielded a further 21 strains. Positive sites included taps, sink drains, and potable water. Genotyping using ERIC-PCR and pulsed-field gel electrophoresis revealed that two pairs of patients' nebulizers were contaminated with closely related strains. None of the S. maltophilia isolates obtained from the ward environment shared genotypes with those obtained from the nebulizers. The frequency of isolation of S. maltophilia from potable water sources on the ward suggests that contamination may result from using it to clean reusable nebulizer equipment, particularly if this is followed by inadequate drying. Although the actual source of S. maltophilia contamination of hospital-use nebulizer equipment in this study remained elusive, these results have important infection control implications.

Introduction

The prevalence of Stenotrophomonas maltophilia respiratory tract colonization in cystic fibrosis (CF) patients has been increasing. Over 10% of CF patients in the United States1 have positive sputum cultures for the bacterium. Rates are even higher in many European CF units.2 S. maltophilia has been readily isolated from the home and hospital environment of patients with CF,3 although the mode of acquisition and potential routes of transmission of the bacterium remains uncertain. Circumstantial evidence implicates nebulizer equipment as a potential source of S. maltophilia for some of these patients. A case–control study analysing risk factors for S. maltophilia colonization in CF showed a significant association with prior use of aerosolized tobramycin (but not colistin).4 Nebulizer equipment is rinsed routinely with tap water in between use and tap water is frequently contaminated with S. maltophilia.3 The bacterium is known to adhere to and form biofilms on plastics.5 Biofilm formation has also been shown to protect the bacterium against the very high concentrations of tobramycin (16 000 μg/mL), which would be encountered inside the atomizer chamber of a nebulizer delivering therapy.6 S. maltophilia has also been isolated from home-use nebulizers.7 Hutchinson et al.7 examined 35 home-use nebulizers from CF patients for the presence of colistin-resistant Gram-negative bacteria and found four (11%) were contaminated with S. maltophilia. Finally, during a study analysing the efficacy of long-term aerosolized tobramycin for CF patients chronically colonized with Pseudomonas aeruginosa, 41 of 258 patients (16%) receiving nebulized tobramycin and 58 of 262 patients (22%) receiving nebulized placebo became colonized with S. maltophilia during the 15-month trial period.8

We studied the contamination rate of hospital-use nebulizer equipment with S. maltophilia in an adult cystic fibrosis centre. The ward environment was also sampled for the presence of S. maltophilia. Genotyping was then used to examine whether any strains contaminating nebulizer equipment were likely to have originated from the ward environment, particularly the hospital water supply.

Section snippets

Methods

The study was conducted in the Adult Cystic Fibrosis Unit (ACFU) at Seacroft Hospital, Leeds, UK. The ACFU provides care for over 250 CF patients from the age of 16 years onwards. Patients receive their care in one of 12 single rooms, all of which contain sinks, but only one of which has an en-suite toilet. There is one bathroom, one shower room and four communal toilets. Between September 1999 and September 2000 disposable components (atomizer chamber, connector, mouthpiece) of nebulizer

Results

A total of 267 components from 89 hospital-use nebulizers were submitted for microbial sampling. Fourteen components (two mouthpieces, seven atomizer chambers, five connectors) from nine (10%) nebulizers were positive for S. maltophilia. Seventy-three environmental sites were sampled (42 tap swabs, 14 sink drain swabs, 12 water samples, two ice machine swabs, two toilet swabs, one dishwasher swab). Seventeen (23%) ward environment sites yielded S. maltophilia, (12 sink drains, three taps and

Discussion

The practice of rinsing reusable nebulizer equipment with tap water in between use is common in CF units. However, there are concerns that organisms frequently found in tap water, such as S. maltophilia, may adhere to the plastic and form bioflms5 if equipment is not dried properly. Indeed the examination of home-use nebulizer equipment by Hutchinson et al.7 suggested that CF patients paying close attention to thorough drying had the lowest incidence of nebulizer contamination.7

The S.

Acknowledgements

We thank staff in the Infection Control Laboratory of the Leeds Teaching Hospitals NHS Trust for their assistance in genotyping the isolates.

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