Severe bilateral pleuropneumonia caused by Legionella sainthelensi: a case report

Background Legionella spp. are ubiquitous freshwater bacteria responsible for rare but potentially severe cases of Legionnaires’ disease (LD). Legionella sainthelensi is a non-pneumophila Legionella species that was first isolated in 1980 from water near Mt. St-Helens (USA). Although rare cases of LD caused by L. sainthelensi have been reported, very little data is available on this pathogen. Case presentation We describe the first documented case of severe bilateral pleuropneumonia caused by L. sainthelensi. The patient was a 35-year-old woman with Sharp’s syndrome treated with long-term hydroxychloroquine and corticosteroids who was hospitalized for an infectious illness in a university hospital in Reunion Island (France). The patient’s clinical presentation was complicated at first (bilateral pneumonia, multiloculated pleural effusion, then bronchopleural fistula) but her clinical condition eventually improved with the reintroduction of macrolides (spiramycin) in intensive care unit. Etiological diagnosis was confirmed by PCR syndromic assay and culture on bronchoalveolar lavage. Conclusions To date, only 14 documented cases of L. sainthelensi infection have been described worldwide. This pathogen is difficult to identify because it is not or poorly detected by urinary antigen and molecular methods (like PCR syndromic assays that primarily target L. pneumophila and that have only recently been deployed in microbiology laboratories). Pneumonia caused by L. sainthelensi is likely underdiagnosed as a result. Clinicians should consider the possibility of non-pneumophila Legionella infection in patients with a compatible clinical presentation when microbiological diagnostic tools targeted L. pneumophila tested negative.


Background
Legionella spp. are ubiquitous Gram-negative freshwater bacteria that can cause sporadic or epidemic human infections, notably severe pneumonia. The main species responsible for Legionnaires' disease (LD) is Legionella pneumophila, which accounts for more than 95% of community-acquired LD worldwide [1,2]. The most frequently reported non-pneumophila Legionella (NP-L) species are L. longbeachae, L. micdadei, L. bozemanii, and L. dumoffii. Less common is Legionella sainthelensi, which was first isolated in 1980 from water near Mt. St-Helens (USA) [1,3]. Here we report a case of L. sainthelensi infection in Reunion Island, a French overseas department and subtropical volcanic island located in the Southwest Indian Ocean, close to Madagascar. This is the first documented case of severe bilateral pleuropneumonia caused by L. sainthelensi. . A second control CT-scan performed on Day 10 showed the persistence of multiloculated pleural effusion and the appearance of bronchopleural fistula in the left lower lobe ( Fig. 1a and b). Pleural fluid collected on Day 5 was retrospectively reanalyzed and tested positive for Legionella spp. (Ct 28.40). Biochemical analyses of pleural fluid showed parapneumonic pleural effusion with excudate (total protein: 49 g/L; LDH: 1156 IU/L; pH: 7.3 and glucose 2.1 mmol/L).

Open Access
The French National Reference Center for Legionella confirmed the identification of L. sainthelensi by MIP  Minimum inhibitory concentrations (MICs) determined using the broth microdilution method were similar to those reported for wild-type L. pneumophila strains (0.032 mg/L for moxifloxacin, 0.016 mg/L for levofloxacin, 0.063 mg/L for erythromycin and azithromycin, and 0.001 mg/L for rifampicin) [5].
Three weeks after admission, the patient's general health improved and she was sent home.

Discussion and conclusions
Here, we reported the first case of severe bilateral pleuropneumonia caused by L. sainthelensi. To our knowledge, only 14 documented cases of L. sainthelensi infection have been reported to date, 9 of which were detected during 2 outbreaks in Canada in 1994 (Table 1) [6][7][8][9]. Interestingly, as in the case reported here, several environmental strains of L. sainthelensi have been found in volcanic environments [10].
New molecular biology tools, and in particular PCR syndromic assays targeting atypical microorganisms, can help confirm the diagnosis of pneumonia caused by NP-L species. Indeed, some marketed kits are able to detect these species even though they are not specifically designed to do so (i.e. Genesig or FTD targeting L. pneumophila and L. longbeachae). However, they are rarely used at the moment because their introduction is fairly recent and because they are costly and expertisedemanding. In this context, the number of cases of pneumonia caused by NP-L species is likely underestimated.
This case report indicates that good communication between medical practitioners and clinical microbiologists is needed to ensure the best complementary investigations are performed in cases of clinical suspicion of LD. As regards our patient, a search for Legionella spp. would likely have allowed an earlier etiological diagnosis. Although culture has limited sensitivity, strain isolation is required for molecular diagnosis confirmation and for epidemiological monitoring by national and international networks [11,12].
Given the limited availability of data, it is difficult to determine whether infections caused by L. sainthelensi are more severe than those caused by other Legionella species (notably L. pneumophila). It should be noted, however, that a case-fatality rate of 13.8% was reported in the only 2 documented outbreaks linked to L. sainthelensi (in Canada). This is slightly higher than the case-fatality rate of 8-9% reported by various surveillance networks [8,11,12]. Lastly, our case report reveals a new category of at-risk patients: namely, young people receiving immunosuppressive treatment [13].
Our patient tested negative twice on the urinary antigen test. This is likely because the test specifically targeted L. pneumophila serogroup 1, which accounts for the great majority of LD cases worldwide (95.4% in France) [11]. Accordingly, in cases of strong clinical or radiological suspicion of LD, and especially in the presence of severity criteria, treatment with antibiotics targeting atypical germs (i.e. Legionella spp., Chlamydophila pneumoniae, and Mycoplasma pneumoniae) should be continued even when the urinary antigen test is negative [14]. In the case of our patient, the right decision was made in reintroducing macrolides when her clinical condition began to deteriorate. Although spiramycin is not recommend as first-line therapy, its use is accepted by French and European guidelines because it causes less drug interactions than the recommended treatment (azithromycin and levofloxacin) and because it is available in injectable form in France [15].
Clinicians should be aware that LD can be caused by NP-L species, which are not detected by urinary antigen testing. At the moment, pneumonia caused by L. sainthelensi is likely underdiagnosed, as the few PCR syndromic assays that can detect NP-L species are rarely used at the moment. Dialogue between clinicians and microbiologists and PCR assays targeting all Legionella spp. are needed to detect NP-L, which can be responsible for severe (albeit rare) cases of LD.