TO THE EDITOR:
Patients with cystic fibrosis (CF) are recommended to wash and disinfect their nebulizers
on a regular basis, ideally after each use,
1
both to ensure that devices are maintained properly for optimal drug delivery and
to minimize infection risks. In practice, approaches to nebulizer hygiene vary among
pediatric
2
,
3
and adult patients, both in the home
2
and hospital environments.
4
Recently, Riquena et al.
5
demonstrated a contamination rate of 71.6% of the nebulizers used by CF patients who
were chronically colonized with Pseudomonas aeruginosa. Nebulizers were contaminated
with clinically significant organisms, including Stenotrophomonas maltophilia (11.9%),
nonmucoid P. aeruginosa (4.8%), Staphylococcus aureus (4.8%), and Burkholderia cepacia
complex (2.4%), as well as yeasts and filamentous fungi. Overall, such contamination
was exacerbated by the use of tap water and outdoor drying of nebulizers, concurrent
with poor nebulizer hygiene among patients.
Recently, CF centers in the United Kingdom highlighted a common practice to wash and
store clean devices in sealed plastic boxes.
4
Given that there is no evidence in the published literature regarding microorganisms
found in nebulizer storage boxes, we examined the microbiology of such boxes used
during inpatient stays to help guide safe practice recommendations for the storage
of nebulizers after cleaning/disinfection.
We collected 24 disposable plastic storage boxes (approximate dimensions: 152 mm in
length × 98 mm in width × 68 mm in depth) used during inpatient stays from 15 pediatric
patients and a new/unused control box. All microbiological analyses were performed
blinded. Microbiology rinse cultures were performed aseptically on each box by adding
18 mL of 0.1% (w/v) peptone saline diluent (CM0733; Oxoid Ltd., Basingstoke, United
Kingdom) into the box and agitating the diluent for 10 min. Resulting rinses were
cultured aerobically on Columbia agar (CM0331; Oxoid Ltd.) supplemented with 5% (v/v)
defibrinated horse blood (SR0050; Oxoid Ltd.) at 37°C/48 h, as well as in nonselective
enrichment broth (Mueller-Hinton Broth; CM0405; Oxoid Ltd.) at 37°C/48 h and on Sabouraud
dextrose agar with chloramphenicol (PO0161; Oxoid Ltd.) at 25°C/5 days, for the detection
of yeasts/fungi. Resulting bacterial colonies were identified using matrix-assisted
laser desorption/ionization, time-of-flight mass spectrometry, and fungal colonies
were identified using internal transcribed spacer/PCR/DNA sequencing. Microbiological
analysis of boxes was subsequently compared with contemporary sputum microbiology
from respective patients.
Eighty percent of the patients had at least one of their storage boxes positive for
bacteria (Table 1). Overall, 20 boxes (83%) were positive for bacteria; however the
majority of these (65%) had a contamination rate of < 103 CFU/box, whereas 15% of
positive boxes were contaminated between 103-104 CFU/box, with the remainder (20%)
contaminated between 104-105 CFU/box. The most highly contaminated box harbored 5.4
× 104 CFU/box. Bacterial diversity demonstrated a predominately gram-positive flora,
representing 15 genera and 22 species. Micrococcus luteus and Dermacoccus nishinomiyaensis
were the most commonly isolated species, with coagulase-negative staphylococci and
the viridans group (oral) streptococci having the greatest species diversity within
their respective genera. Gram-negative bacteria were in the minority, representing
8.3% of bacterial species isolated, namely Stenotrophomonas maltophilia and Neisseria
flava/perflava/subflava. Fungi were isolated from 4 (26.7%) of 15 boxes and included
Penicillium sp., Penicillium expansum, Cladosporium sp. and Candida albicans.
Table 1
Comparison between microbial contaminants found in plastic storage boxes used to store
nebulizers and current sputum microbiology in patients with cystic fibrosis.
Patient
Box
Sputum
1
Staphylococcus epidermidis
Pseudomonas aeruginosa
2
Micrococcus luteus, Dietzia cinnamea
MRSA
3
Staphylococcus capitis, Dermacoccus nishinomiyaensis, Kocuria rhizophila, Corynebacterium
afermentans, Paenibacillus macerans, Bacillus licheniformis
Pseudomonas aeruginosa
4
Micrococcus luteus, Gemella haemolysans, Streptococcus sanguinis, Rothia aeria, Rothia
dentocariosa, Dermacoccus nishinomiyaensis, Bacillus licheniformis, Kocuria rhizophila,
Streptococcus parasanguinis, Rothia mucilaginosa
Stenotrophomonas maltophilia
5
Streptococcus parasanguinis, S. mitis, S. oralis, Streptococcus sp., Neisseria flava,
N. perflava, N. subflava
Yeasts
6
Staphylococcus warneri, Stenotrophomonas maltophilia, Microbacterium paraoxydans,
Bacillus licheniformis, Penicillium expansum, Penicillium spp., Candida albicans
Pseudomonas aeruginosa
7
No growth
MRSA
8
Micrococcus luteus
Long-standing ABPA
9
Streptococcus mitis, S. oralis, S. sanguinis, S. parasanguinis
Pseudomonas aeruginosa
10
Micrococcus luteus, Bacillus sp., unidentified fungus
Staphylococcus aureus
11
Micrococcus luteus
Staphylococcus aureus
12
Staphylococcus saprophyticus, Dermacoccus nishinomiyaensis,Cladosporium spp.
Staphylococcus aureus, Haemophilus influenzae, Stenotrophomonas maltophilia
13
Brevibacillus sp., Dermacoccus nishinomiyaensis, unidentified fungus
Pseudomonas aeruginosa
14
No growth
Pseudomonas aeruginosa, Staphylococcus aureus, ABPA
15
No growth
Staphylococcus aureus, Haemophilus influenzae
Control
Staphylococcus epidermidis
New control box
MRSA: methicillin-resistant Staphylococcus aureus; and ABPA: allergic bronchopulmonary
aspergillosis.
With the exception of Stenotrophomonas maltophilia, none of the organisms identified
are considered major pathogens of CF. None of the boxes grew organisms which were
contemporary to the organisms found in patients’ sputum (Table 1). Most of the organisms
identified were of skin, mouth, or throat/oropharyngeal origin. In contrast to Riquena
et al.,
5
a recent study in the USA
3
found contamination of nebulizers used by pediatric CF patients, the most frequently
observed microbial contaminants being viridans streptococci, Micrococcus sp., coagulase-negative
staphylococci, and Candida albicans. Our findings in relation to storage boxes largely
concur with those of the US report
3
in terms of bacterial contamination. Our study demonstrated the presence of yeast
and fungal contaminants, similar to the Brazilian report.
5
The occurrence of fungi may be due to inadequate drying of nebulizer parts prior to
storage, which emphasizes the importance of thorough drying prior to storage.
Therefore, what is the significance of the storage boxes being largely contaminated
with oral and environmental organisms? Although the organisms detected are not believed
to be clinically significant, such organisms may harbor antibiotic resistance gene
determinants and, if nebulized, could provide a reservoir for such determinants to
be horizontally transferred to established CF pathogens in the lung, thereby potentially
increasing the antimicrobial resistance burden. Studies are therefore required to
elucidate the potential for such horizontal gene transfer events from nonpathogenic
to pathogenic organisms.
The efficiency of nebulizer cleaning and disinfection will directly affect the hygienic
status of boxes, used subsequently for the storage of nebulizers. Therefore, in alignment
with current evidence, patients should wash and disinfect their nebulizers after each
use with steam disinfection in a baby bottle disinfector and leave their nebulizers
in such disinfector units until next required.
6
Where storage in the steam disinfector is not practical, then, after disinfection,
nebulizers should be air dried fully and stored on absorbent tissue in dedicated clean
storage boxes, separate from those used to wash nebulizers.