S. maltophilia pneumonia: A case report.

Case report of Community-acquired pneumonia in a male patient without co-morbidities. Empiric antibiotic treatment did not resolve the clinical picture of productive cough, and a chest computerized tomography and sputum culture with antibiogram were performed, identifying S. maltophilia infection with sensitivity to levofloxacin and sulfamethoxazole/trimethoprim. Treatment with levofloxacin (500 mg/day for 15 days) resulted in resolution of the clinical picture.

Introduction

Stenotrophomonas maltophilia is a gram-negative and non-fermentative aerobic bacterium, considered an opportunistic pathogen due to its low virulence [1]. However, S. maltophilia presents several characteristics, including its ability to survive and colonize on humid surfaces, a tendency to biofilm formation on abiotic and biotic surfaces (including pulmonary cells), and the use of various mechanisms of resistance to various antimicrobial agents, which contribute to infection-associated risk factors [2]. S. maltophilia is commonly associated with respiratory tract infection and may also infect the eyes, biliary system (leading to biliary sepsis), bones and joints, and the urinary system, among others [1].

Case report

A 61-year-old male patient, without comorbidities, had persistent productive cough for 5 months, with two episodes of chills and fever in this period. During this period, the patient used aminophylline (400mg/day), deflazacort (60mg/day), and formoterol + budesonide fumarate (24/800/day) intermittently and without significant cough improvement. After a 20-day course of amoxicillin + clavulanate potassium (875/125mg), followed by clarithromycin (500mg/day for 14 days), blood tests and a computed tomography scan of the chest were requested.

The blood test revealed elevation of C-reactive protein (1.5) leukocytosis (16,600/mm3), segmented 85%, lymphopenia (9%) and BSR elevation (36mm/h). Computed tomography of the thorax was performed, showing centrilobular nodular opacities in the left lower lobe, due to filling of small airways, bronchi with thickened walls, some partially filled. Facial glass nodular opacities were also observed in the apicoposterior segment of the upper left lobe, measuring 1 cm. Small, sparse non-calcified nodular opacities measuring <0.03cm present bilaterally. Opacity in a fibroatelectasic range in the medial segment of the middle lobe. Absence of lymphadenomegaly or pleural effusion (Fig. 1, Fig. 2).

Fig. 1

CT image showing centrilobular nodular opacities in the left lower lobe and facial glass nodular opacities in the apicoposterior segment of the upper left lobe. Small, sparse non-calcified nodular opacities <0.03cm present bilaterally.

Fig. 2

CT image showing opacity in a fibroatelectasic range in the medial segment of the middle lobe.

Sputum examination (performed by automated culture) with antibiogram identified the bacterium Stenotrophomonas maltophilia, with sensitivity to levofloxacin and sulfamethoxazole/trimethoprim. Treatment with levofloxacin (500 mg/day for 15 days) resulted in resolution of the cough.

Discussion & conclusion

Community-acquired pneumonia is defined as pneumonia contracted outside the hospital setting and is among the most common infectious diseases in the general population and is identified as a major cause of mortality and morbidity worldwide. About 85% of cases are caused by three bacteria: Streptococcus pneumonia, Haemophilus influenza, and Moraxella catarrhalis. Less frequently (∼15% of cases), the following microorganisms are identified as the etiological agent: Chlamydophila psittaci, Coxiella burnetii, and Francisella tularensis, Mycoplasma pneumoniae, Legionella spp and Chlamydia pneumoniae (the latter three being considered non-zoonotic atypical pathogens) [3].

Empirical treatment of pneumonia is recommended immediately according to the following therapeutic regimens (oral route). For patients without comorbidities and in the absence of risk factors for resistant S. pneumoniae: Azithromycin (500 mg once daily followed by 250 mg daily for 4 days or 2 g prolonged single dose); Clarithromycin (500mg twice daily or 1000mg prolonged release in single daily dose); or Doxycycline (100mg twice daily). In the case of prior antibiotic therapy within 3 months, therapeutic options include: azithromycin or clarithromycin together with amoxicillin 1g every 8 hours or amoxicillin and clavulanate 2g every 12 hours; or respiratory fluoroquinolone (levofloxacin or moxifloxacin). In the presence of comorbidities, options include levofloxacin 750mg daily, moxifloxacin 400mg daily, or a combination beta-lactam antibiotic such as amoxicillin together with a macrolide (azithromycin or clarithromycin). The minimum duration of therapy is 5 days, and prolonged treatment may be necessary in case of complications [3,4].

Risk factors associated with S. maltophilia infection include malignancy, organ transplantation, human immunodeficiency virus (HIV) infection, chronic obstructive pulmonary disease, cystic fibrosis, prolonged hospital stay, intensive care unit admission, mechanical ventilation, permanent catheter therapy, corticosteroid or immunosuppressive therapy, and recent antibiotic treatment [2]. Resistance to antimicrobial agents is an important topic in the discussion of S. maltophilia infections; the World Health Organization classifies it as one of the leading multidrug resistant organisms in hospital settings [5]. S. maltophilia's increasing propensity towards drug resistance has been widely reported, with proposed mechanisms ranging from expression of environmentally-acquired resistance genes to decreased outer membrane permeability, in addition to chromosomal and plasmid-encoded transposons, β-lactamase production, integrons, and biofilms, as well as multidrug efflux pumps [1,5,7].

S. maltophilia is associated with nosocomial infections among patients presenting immunodeficiencies, with cases isolated in the literature from involvement in healthy individuals [6]. However, the prevalence of S. maltophilia infections has increased in the general population from 0.8 to 1.14% in the period 1997–2003 to 1.3–1.68% between 2007 and 2012 [7]. Complementary exams such as sputum culture represent an important tool in the diagnostic confirmation and implementation of therapy appropriate to each case. In the case of this patient, the culture identified the presence of S. maltophilia and the antibiogram showed to sensitivity to two antibiotics (levofloxacin and sulfamethoxazole/trimethoprim). In this case, treatment with levofloxacin was successful in resolution of the patient's persistent productive cough.

Funding sources

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declarations of interest

None.