Concomitant presence of Aspergillus fumigatus and Stenotrophomonas maltophilia in the respiratory tract: a new risk for patients with liver disease?

Abstract

Concomitant lung colonization by Aspergillus fumigatus and Stenotrophomonas maltophilia was reported mainly in patients with cystic fibrosis (CF) and immunocompromised patients. The aim of the study was to assess the frequency of co-culture of A. fumigatus and S. maltophilia in respiratory samples of hospitalized patients, and to determine its associated factors. Between 2007 and 2011, all patients who had A. fumigatus in their respiratory samples were retrospectively enrolled in the study. Their clinical and laboratory data, including the presence of S. maltophilia in a respiratory sample, were collected within the same month. Of the 257 enrolled patients (372 respiratory samples), 71 % were immunocompromised and 32 % had chronic respiratory disease. S. maltophilia was isolated within the same month in 20 patients (7.8 %). In the univariate analysis, factors associated with concomitant culture of A. fumigatus and S. maltophilia were liver disease (P = 0.009), orotracheal intubation (P = 0.001), ventilator-associated pneumonia (P = 0.006), central venous catheter (P = 0.003), parenteral nutrition (P = 0.008) and culture of Pseudomonas aeruginosa in respiratory samples (P = 0.002). In the multivariate analysis, the simultaneous presence of P. aeruginosa in the respiratory tract (odds ratio (OR) = 3.19, 95 % confidence interval (CI) 1.11–9.14, P = 0.031), liver disease (OR = 3.92, 95 % CI 1.32–11.62, P = 0.014) and orotracheal intubation (OR = 3.42, 95 % CI 1.17–9.96, P = 0.024) were independently associated with the co-culture of S. maltophilia and A. fumigatus. Factors independently associated with the concomitant culture of A. fumigatus and S. maltophilia were identified. These results support a future prospective study focusing on liver disease and its complications.

Introduction

Over the past decade, Aspergillus fumigatus has become the major air-borne fungal pathogen in developed countries, incurring an increasing incidence of aspergillosis (Lass-Flörl, 2009; Lortholary et al., 2011). This fungus is traditionally isolated in samples from patients with haematological diseases, stem cell or solid organ transplant, or on long-term corticotherapy, thus causing invasive infections (De Pauw et al., 2008). Recent studies have described A. fumigatus colonization in patients with chronic lung diseases, especially chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF), probably due to lung structural changes and the heavy courses of antibiotics (Bafadhel et al., 2014; Sabino et al., 2014). Furthermore, co-morbidities such as alcoholism, diabetes, malnutrition and liver cirrhosis are often associated with this A. fumigatus colonization (Prodanovic et al., 2007).

One of the emerging micro-organisms concomitantly isolated with A. fumigatus from the respiratory tract of immunocompromised patients or those suffering from chronic respiratory diseases is Pseudomonas aeruginosa, a non-fermentative Gram-negative bacillus and one the most studied bacteria (Baxter et al., 2013). Other bacteria, such as Stenotrophomonas maltophilia, have recently emerged as important hospital-associated pathogens colonizing the same type of patients. This intrinsically multidrug-resistant, saprophytic and ubiquitous micro-organism belongs to the ‘Pseudomonas and parented’ group of bacteria, and is increasingly encountered in human infectious diseases (Jacquier et al., 2011). Although not highly virulent, its environmental spread and resistance to antibiotic selective pressure promote its opportunistic pathogenicity in immunocompromised patients. Risk factors that are associated with S. maltophilia infections and/or colonization are often shared with Aspergillus infections. These risk factors include immunosuppressive or corticosteroid therapy and history of long-term intake of broad-spectrum antibiotics (Brooke, 2012).

Fungi and bacteria are often simultaneously cultivated from respiratory tract specimens, but the physiopathological, biological and clinical relevance of the microbial association remains controversial (Wargo & Hogan, 2006; Peleg et al., 2010; Frey-Klett et al., 2011). In CF, significant associations have been reported between the upper airway colonization by A. fumigatus and the presence of S. maltophilia (Marchac et al., 2004; Paugam et al., 2010), or the presence of P. aeruginosa or atypical mycobacteria (Amin et al., 2010; Paugam et al., 2010). Similarly, bronchial colonization by S. maltophilia is independently associated with the development of allergic bronchopulmonary aspergillosis (Ritz et al., 2005). If the association between A. fumigatus and S. maltophilia is well established in CF patients, it needs to be confirmed in other clinical settings and particularly in immunocompromised patients and other disease sufferers.

The aim of this work was to assess, beyond the CF context, the frequency of concomitant respiratory presence of A. fumigatus and S. maltophilia in hospitalized patients, and the factors associated with this co-presence.

Methods

Patients, settings and specimens

The study had a cross-sectional, retrospective design and was conducted from February 2007 to December 2011 in Henri Mondor University Hospital. This 900-adult bed, tertiary care institution, which is located in the suburb of Paris (France), provides care to a large panel of immunocompromised patients [solid organ transplantation, haematopoietic stem cell transplantation, immunosuppressive treatment and intensive care unit (ICU)].

The case definition was a patient who had at least one respiratory sample (sputum, tracheal aspirate, plugged telescoping catheter, protected sample brush, bronchoalveolar lavage or sinusal sample) yielding an A. fumigatus-positive culture during the study period. For each case patient, the presence of bacteria in the same respiratory sample or in another sample drawn during a 1-month period from the culture of A. fumigatus was collected. The presence, in the same period, of these two micro-organisms in the airway reflects either colonization or infection. Invasive aspergillosis was classified as proven, probable, possible or excluded according to the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) criteria (De Pauw et al., 2008). The microbiological data were extracted from the database of the microbiology laboratory. The medical charts were retrospectively reviewed and the following clinical data were collected: demographic features, underlying disease, history of invasive procedure or 1 month of antimicrobial therapy preceding the A. fumigatus and/or S. maltophilia colonization, time period between hospitalization and A. fumigatus and/or S. maltophilia identification, duration of hospital stay, and clinical outcome.

Processing of the respiratory samples in the microbiology laboratory

The respiratory samples were cultured for both filamentous fungi and bacteria following the European Society of Clinical Microbiology and Infectious Diseases Guidelines (Freymuth et al., 2012). As such, Sabouraud chloramphenicol gentamicin agar (bioMérieux) was inoculated in order to identify filamentous fungi. Considering the bacteria, the specimens were cultured as described previously (Nebbad-Lechani et al., 2013) with Trypticase soy, Drigalski, colistin nalidixic acid sheep blood and chocolate agar supplemented with PolyViteX.

Statistical analysis

The clinical and microbiological characteristics of the micro-organism population were presented as n (%), mean ± sd or median (25th–75th percentiles), as appropriate. Frequencies of colonization by A. fumigatus/S. maltophilia and other bacteria were expressed as percentage and 95% confidence interval (95% CI) based on binomial distribution.

The clinical and microbiological characteristics of patients with and without concomitant A. fumigatus/S. maltophilia colonization were compared using the Pearson χ²-test or Fisher test for qualitative variables and the Student t-test or Wilcoxon–Mann–Whitney test for quantitative variables, as appropriate.

First, all variables with P < 0.15 in the univariate analysis were selected for the multivariate analysis. Second, a bivariate analysis was performed to identify potential confounders. In the final multivariate logistic regression model, only variables which remained significantly and independently associated with colonization by A. fumigatus/S. maltophilia at P < 0.05 were included. The same methodology was used to assess factors associated with in-hospital death.

Interactions were checked. Adjusted odd ratios (ORs) with their 95 % CIs were estimated. All tests were two-tailed. The threshold of significance was fixed at P < 0.05. No imputation of missing data was made. The data were analysed using r software (www.r-project.org).

Results

Between February 2007 and December 2011, 257 patients with at least one positive A. fumigatus culture were enrolled in the study (Group A patients). The origin of the specimen was sputum (n = 129), tracheal aspirate (n = 53), plugged telescoping catheter (n = 19), protected sample brush (n = 1), bronchoalveolar lavage (n = 156) or a sinusal sample (n = 14). The clinical and microbiological characteristics of this population are summarized in Table 1. The mean ± sd age was 59.4 ± 14.6 years and 176 patients (68 %) were male.

Table 1. Clinical and bacteriological characteristics of the 257 enrolled in-patients.

			S. maltophilia culture
Characteristics	Missing data	All patients (n = 257)	Negative (n = 237)	Positive (n = 20)	P-value*
Age (years)	0	59 ± 15	59 ± 15	62 ± 9	0.39
Male	0	176 (68)	163 (69)	13 (65)	0.73
Underlying disease
Malignancies
Haematological malignancy	4	118 (47)	112 (48)	6 (30)	0.13
Cancer	7	45 (18)	40 (17)	5 (25)	0.4
Solid organ transplantations
Liver transplantation	4	17 (7)	13 (5)	4 (20)	0.03
Kidney transplantation	4	20 (8)	19 (8)	1 (5)	–
Stem cell transplantation	4	38 (15)	36 (15)	2 (10)	–
Other diseases
Liver disease†	6	36 (14)	29 (13)	7 (35)	0.009
Chronic respiratory disease	4	69 (32)	65 (33)	4 (25)	0.53
Human immunodeficiency virus infection	7	7 (3)	7 (3)	0 (0)	–
Neutropenia	4	37 (15)	34 (15)	3 (15)	0.96
Immune system disorders	6	40 (16)	37 (16)	3 (15)	0.91
Immunosuppressive treatments
Immuno- and biotherapy	34	147 (66)	134 (66)	13 (68)	0.81
Anti-neoplasic chemotherapy	12	72 (29)	69 (31)	3 (15)	0.15
Corticotherapy	39	109 (50)	99 (50)	10 (56)	0.62
Invasive procedures‡
Orotracheal intubation	15	38 (16)	29 (13)	9 (45)	0.001
Ventilator-associated pneumonia	10	8 (3)	5 (2)	3 (16)	0.006
Central venous catheter	56	75 (37)	61 (34)	14 (70)	0.003
Parenteral nutrition	74	13 (7)	9 (5)	4 (25)	0.008
Dialysis	8	18 (7)	16 (7)	2 (10)	–
Broad-spectrum antibiotics‡	52	93 (45)	81 (44)	12 (63)	0.11
Time period between admission and A. fumigatusand/or S. maltophilia isolation‡ (days)	0	9 (0–327)	8 (0–175)	27 (0–327)	< 0.001
Death during hospitalisation	5	52 (20)	42 (18)	10 (50)	0.002
Bacteria in respiratory specimen
Pseudomonas aeruginosa	0	53 (21)	43 (18)	10 (50)	0.002
Escherichia coli	0	14 (5)	11 (5)	3 (15)	0.065
Staphylococcus aureus	0	17 (7)	14 (6)	3 (15)	0.131
Others	0	139 (54)	135 (56)	4 (20)	< 0.001*

Data are presented as n (%) for qualitative variables and as mean ± sd or median (25th–75th percentile) for quantitative variables as appropriate.

^*Pearson χ²-test/Fisher test or Student t-test/Wilcoxon–Mann–Whitney test as appropriate.

^†Liver disease: cirrhosis (n = 15) or others (n = 21).

^‡In samples taken within the 1-month period from A. fumigatus culture.

Most of the patients were immunocompromised (71 %) due to different diseases. They received immunosuppressive therapy for haematological malignancy (n = 118), including 38 haematopoietic stem cell receivers, solid organ transplantation (n = 39), cancer (n = 45) or other causes (Table 1). Of the 39 patients with solid organ transplantation, 16 received liver, 16 kidney, one liver/kidney, one pancreas/kidney, two heart/kidney, two heart and one pancreas transplantation. Of the non-immunocompromised patients, 69 (32 %) had chronic respiratory disease, such as bronchiectasis, COPD and asthma, but none had CF. At inclusion, the most commonly performed invasive procedures on the study patients were mechanical ventilation (n = 38), central venous catheter (n = 75) and parenteral nutrition (n = 13). In addition, 93 patients (45 %) received antimicrobial therapy at the time of A. fumigatus culture, of whom 50 patients (54 %) received a third-generation cephalosporin.

S. maltophilia was isolated in 20 cases of the 257 patients (7.8 %, 95 % CI 4.8–11.8), either on the same day or during the 1-month period from the A. fumigatus culture. Patients with A. fumigatus and S. maltophilia co-culture were defined as ‘Group AS’ patients. The percentage of invasive aspergillosis (proven or probable) was significantly higher in Group AS (13/20, 65 %) than in Group A (89/237, 37 %) (P = 0.016). The annual distribution of the A. fumigatus and S. maltophilia co-culture showed a stable non-significant variable trend over 5 years (eight patients in 2007, two patients in 2008, five patients in 2009, two patients in 2010 and three patients in 2011; P trend = 0.14). Other bacterial pathogens identified in the respiratory samples included P. aeruginosa (n = 53; 20.6 %, 95 % CI 15.8–26.1), Escherichia coli (n = 14, 5.4 %; 95 % CI 3.0–8.9) and Staphylococcus aureus (n = 17; 6.6 %, 95 % CI 3.9–10.4); at least one bacterial species was identified in 104 specimens.

In Group AS, both micro-organisms were isolated in the same respiratory sample in 11 out of the 20 cases (55 %), during the same week in five cases (25 %) or the same month in four cases (20 %). However, 16 patients (80 %) were colonized by at least one other different species.

Factors associated with the co-culture of A. fumigatus and S. maltophilia

No significant difference was found for age, sex, immunosuppressive or anti-neoplasic therapy, and corticosteroid regimen between Group A and Group AS (Table 1). In the univariate analysis, significant differences between Group A and Group AS were found for liver disease (cirrhosis, liver transplantation, hepatitis, etc.) (13 versus 35 %, P = 0.009), mechanical ventilation (13 versus 45 %, P = 0.001), ventilator-associated pneumonia (2 versus 16 %, P = 0.006), central venous catheter (34 versus 70 %, P = 0.003), parenteral nutrition (5 versus 25 %, P = 0.008), time period between admission and A. fumigatus and/or S. maltophilia culture (8 versus 27 %, P < 0.001), identification of other bacteria from respiratory samples (P. aeruginosa, 18 versus 50 %, P = 0.002), and at least one bacteria isolated in a respiratory sample (45 versus 80 %, P < 0.001) (Table 1). Finally, death during hospitalization was also significantly different between the two groups (P = 0.002). Interactions were tested (1) between significantly associated underlying condition (liver disease) and different bacteria in the respiratory specimen, and (2) between invasive procedures and different bacteria in the respiratory specimen. No significant interactions were found. The multivariate logistic regression model, adjusted for P < 0.15 in the univariate analysis, showed that the simultaneous presence of P. aeruginosa in the respiratory tract (OR = 3.19, 95 % CI 1.11–9.14, P = 0.031), liver disease (OR = 3.92, 95 % CI 1.32–11.62, P = 0.014) and mechanical ventilation (OR = 3.42, 95 % CI 1.17–9.96, P = 0.024) were independently associated with the co-culture of S. maltophilia and A. fumigatus within the same month (Table 2).

Table 2. Factors associated with S. maltophilia-positive culture in 257 in-patients with already A. fumigatus-positive culture.

Variable	Adjusted OR*	95 % CI	P-value†
Liver disease	3.92	1.32–11.62	0.014
Orotracheal intubation	3.42	1.17–9.96	0.024
P. aeruginosa	3.19	1.11–9.14	0.031

^*Multivariate logistic regression model adjusted for all variables listed in the table.

^†Wald test.

In Group AS, all of the seven patients with liver disease had EORTC/MSG criteria for probable invasive aspergillosis (De Pauw et al., 2008). These patients were all immunocompromised and hospitalized in the ICU when A. fumigatus and S. maltophilia were isolated. Amongst them, four patients had undergone liver transplantation (three for cirrhosis and one for fulminant hepatitis), and two patients had alcoholic cirrhosis and one hepatic acute graft versus host disease after allogenic stem cell transplantation for acute myeloid leukaemia. None had chronic respiratory diseases. S. maltophilia was isolated before A. fumigatus in four cases, A. fumigatus was isolated before S. maltophilia in two cases and both were found in the same sample in one case. All patients were treated for A. fumigatus and S. maltophilia infections with appropriate medicines. Five patients (71 %) died during hospitalization.

In the univariate analysis, factors associated with in-hospital death were liver disease (11.2 % alive versus 23.5 % in-hospital death, P = 0.023), orotracheal intubation (9.4 versus 39.6 %, P < 0.0001), S. maltophilia (5 versus 19.2 %, P = 0.001), E. coli (3 versus 13.5 %, P = 0.002), P. aeruginosa (14 versus 46.2 %, P < 0.0001), immunosuppression (75.3 versus 60 %, P = 0.032), ventilator-associated pneumonia (13.1 versus 47.9 %, P < 0.0001), central venous catheter (27.4 versus 72.5 %, P < 0.0001) and parenteral nutrition (3.9 versus 23.3 %, P < 0.0001).

In the multivariate analysis, factors which independently associated with in-hospital death were P. aeruginosa, liver disease and orotracheal intubation (Table 3). Age >61 years was borderline significant. However, A. fumigatus/S. maltophilia was no longer associated with in-hospital death after adjustment for the three main factors, i.e. P. aeruginosa, liver disease and orotracheal intubation.

Table 3. Factors associated with in-hospital fatality risk in 257 in-patients with already A. fumigatus-positive culture.

Variable	Adjusted OR*	95 % CI	P-value†
Age ≥ 61 years	2.18	0.91–5.24	0.082
Liver disease	3.87	1.25–11.92	0.018
Orotracheal intubation	5.13	1.98–13.29	0.001
S. maltophilia	1.62	0.46–5.63	0.448
P. aeruginosa	4.69	1.85–11.89	0.001

^*Multivariate logistic regression model adjusted for all variables listed in the table.

^†Wald test.

Discussion

In the present study, we have shown that 7.8 % of the hospitalized patients who were carriers of Aspergillus spp. in their lung also harboured S. maltophilia. This concurrent colonization was associated with excess mortality. In this retrospective study, it was sometimes difficult to separate colonization and infection for these two micro-organisms. We identified three risk factors for this microbial association: liver disease, orotracheal intubation and the culture of other pathogenic bacteria in the respiratory specimens, particularly P. aeruginosa.

To the best of our knowledge, this work is the first study interested in the co-culture of A. fumigatus and S. maltophilia in respiratory samples from patients other than CF sufferers. Two previous studies have found an association between the presence of A. fumigatus and subsequent S. maltophilia infection in patients with CF (Marchac et al., 2004; Paugam et al., 2010). In these two studies, the factors associated with contracting S. maltophilia were: more than two consecutive courses of intravenous antibiotics, identification of A. fumigatus in the sputum and oral steroid treatment. With the exclusion of CF, the factors associated with S. maltophilia identification in patients are well known: underlying malignancy, presence of indwelling devices (e.g. catheters), chronic respiratory disease, immunocompromised host, prior use of antibiotics and long-term hospitalization or ICU stay (Brooke, 2012). We found that P. aeruginosa was significantly associated with the co-presence of A. fumigatus and S. maltophilia in the multivariate analysis. Polymicrobial infections by S. maltophilia and other organisms such as P. aeruginosa, Burkholderia spp., Staphylococcus aureus or E. coli in the CF patient's lung were reported previously (Brooke, 2012). P. aeruginosa, associated with S. maltophilia, has the ability to form biofilms on the lung cells in vitro (Pompilio et al., 2010). P. aeruginosa may provide a more hospitable environment for the adherence, invasion and persistence of S. maltophilia in the CF patient's lung (De Vidipó et al., 2001). This may help explain their tendency to cause persistent infections and the vast damage of the epithelial mucosa induced by the exoproducts they release (Looney et al., 2009; Brooke, 2012). Furthermore, S. maltophilia or P. aeruginosa colonization may increase the probability of respiratory tract colonization by A. fumigatus, thus degrading the mucosa and leading to subsequent worsening of respiratory function. These interactions could be compared to the effect of influenza H1N1 infection that provokes invasive pulmonary aspergillosis by impairing the airway epithelium and releasing innate cytokine/chemokine (Martin-Loeches & Valles, 2012).

Interaction of S. maltophilia with other micro-organisms is currently under study. A. fumigatus and S. maltophilia could communicate through secreted factors (quorum sensing molecules, secondary metabolites, carbohydrates and proteins) that would influence the production of biofilm (Pompilio et al., 2010).

S. maltophilia commonly colonizes the lungs of patients with pulmonary disease, particularly CF patients. In our group of 69 patients who had chronic respiratory diseases, the co-presence of both A. fumigatus and S. maltophilia was not significantly higher than in patients without pulmonary diseases. No independent association was found between S. maltophilia and death during hospitalization.

In the multivariate analysis, liver disease was a factor independently associated with such co-presence. All of the seven patients with liver disease suffered from invasive aspergillosis, which reflected their immunocompromised status and the presence of additional risk factors for S. maltophilia colonization, such as antibiotic therapy. As such, those seven patients are at risk of infections precipitated by the significant impairment of the neutrophil defence mechanism, frequent use of corticosteroids and invasive procedures, and malnutrition (Panasiuk et al., 2005; Cheruvattath & Balan, 2007; Falcone et al., 2011; Fishman, 2011; Barchiesi et al., 2015). However, to the best of our knowledge, our study is the first description of an association between co-infection by A. fumigatus and S. maltophilia and patients with liver disease. This study has several limitations. First, this work was a single-centre retrospective study. Nevertheless, its first results encourage us to propose a larger-scale study on A. fumigatus and S. maltophilia co-culture in patients without respiratory diseases. Second, we were not able to distinguish between S. maltophilia infection and colonization, which made it difficult to reach conclusions on the specific role of the bacterium in the pathological process. However, A. fumigatus infections were detected in a specific group of patients, i.e. the liver transplant patients, who presented a propensity to be co-colonized by S. maltophilia. These results should be confirmed in a larger-scale study.

Conclusion

In this study, we identified the prevalence of concomitant colonization by A. fumigatus and S. maltophilia, and the factors independently associated with it. These results support the hypothesis of a particular susceptibility of patients with end-stage liver disease to this co-colonization. Additional complementary epidemiological and physiopathological investigations are needed.

Abbreviations:

CF

cystic fibrosis

CI

confidence interval

COPD

chronic obstructive pulmonary disease

EORTC/MSG

European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group

ICU

intensive care unit

OR

odds ratio