Lomentospora prolificans Disseminated Infections: A Systematic Review of Reported Cases

Background: Lomentospora prolificans, a rare, highly virulent filamentous fungus with high rates of intrinsic resistance to antifungals, has been associated with different types of infections in immunocompromised as well as immunocompetent individuals. Objective: To systematically address all relevant evidence regarding L. prolificans disseminated infections in the literature. Methods: We searched Medline via PubMed and Scopus databases through July 2022. We performed a qualitative synthesis of published articles reporting disseminated infections from L. prolificans in humans. Results: A total of 87 studies describing 142 cases were included in our systematic review. The pathogen was most frequently reported in disseminated infections in Spain (n = 47), Australia (n = 33), the USA (n = 21), and Germany (n = 10). Among 142 reported cases, 48.5% were males. Underlying conditions identified for the majority of patients included malignancy (72.5%), hemopoietic stem cell transplantation (23.2%), solid organ transplantation (16%), and AIDS (2%). Lungs, central nervous system, skin, eyes, heart and bones/joints were the most commonly affected organs. Neutropenia was recorded in 52% of patients. The mortality rate was as high as 87.3%. Conclusions: To the best of our knowledge, this is the first systematic review conducted on disseminated infections due to this rare microorganism. Physicians should be aware that L. prolificans can cause a diversity of infections with high mortality and primarily affects immunocompromised and neutropenic patients.


Introduction
Lomentospora prolificans, formerly known as Scedosporium prolificans or Scedosporium inflatum, is a rare emerging opportunistic pathogen that primarily affects immunocompromised individuals but can also cause infections in healthy populations [1]. It is found in the environment, including soil, decaying organic matter, and contaminated water [2,3]. The first report as a pathogen in humans was in 1984, when Malloch and Salkin isolated this fungus from an immunocompetent patient with osteomyelitis [4].
L. prolificans can grow on standard mycological media such as Sabouraud's dextrose agar (SDA) or potato dextrose agar (PDA) [5]. Characteristic macroscopic features include olive-gray to black colony morphology and susceptibility to cycloheximide [6]. Microscopic features that may indicate the presence of L. prolificans include visualization of flask-shaped conidiophores which are inflated or swollen at the base, from which single, or clusters of, conidia emerge [6].
L. prolificans infection causes a wide range of clinical manifestations from localized to disseminated infections, depending on the immune status of the infected individual [7]. 3

.1. Study Selection
In Figure 1, the PRISMA flow chart reveals the selection process of included studies. With the above-mentioned search terms, we identified 1373 records on Medline via PubMed and 495 additional records on Scopus. After detecting and removing duplicates, 1494 articles remained, among which we initially excluded 1394 because of study design. Subsequently, we examined in detail the remaining 100 articles. Among them, 13 studies were rejected because selection criteria were not met (Supplementary Table S1 and Figure 1). Finally, 87 studies with a total of 142 cases (patients with disseminated L. prolificans infection) were included in our systematic review.

Quality Appraisal
The overall quality was very good, as 72 articles had a low risk of bias, while 9 studies had a high risk of bias and 6 studies had a moderate risk of bias. Quality appraisal results are presented in Supplementary Table S2.

Discussion
The current systematic review focuses on disseminated infections caused by L. prolificans in humans. To the best of our knowledge, this is the first systematic review conducted on disseminated infections due to this rare microorganism.
L. prolificans is a rare filamentous fungus found primarily in the environment, including soil, decaying organic matter, and contaminated water [2,3]. Regarding the epidemiology of L. prolificans disseminated infection, cases were initially reported in the dry climates of Spain, Australia and the southwestern United States. Recently, however, there have been publications from other countries, specifically Germany, Japan, France, Mexico, The Netherlands, Canada, South Korea, Italy, Brazil, Belgium, Thailand, Poland, and India ( Figure 2). Excluded studies due to different language concern cases reported in the aforementioned countries (Supplementary material).
icans in humans. To the best of our knowledge, this is the first systematic review conducted on disseminated infections due to this rare microorganism.
L. prolificans is a rare filamentous fungus found primarily in the environment, including soil, decaying organic matter, and contaminated water [2,3]. Regarding the epidemiology of L. prolificans disseminated infection, cases were initially reported in the dry climates of Spain, Australia and the southwestern United States. Recently, however, there have been publications from other countries, specifically Germany, Japan, France, Mexico, the Netherlands, Canada, South Korea, Italy, Brazil, Belgium, Thailand, Poland, and India ( Figure 2). Excluded studies due to different language concern cases reported in the aforementioned countries (Supplementary material). This pathogen can infect both immunocompetent and immunocompromised patients and thus acts both as a primary and an opportunistic pathogen [100]. Skin, soft tissue, This pathogen can infect both immunocompetent and immunocompromised patients and thus acts both as a primary and an opportunistic pathogen [100]. Skin, soft tissue, muscle, bone, and joint infections are more common in immunocompetent hosts, and infection usually requires disruption of the anatomic barrier by trauma, surgery, or corticosteroid injections [1,101]. Almost all cases presented in this review involve diseases and conditions indicative of severe immunosuppression. Airway colonization is common in patients with cystic fibrosis and lung transplantation [1,102,103]. Structural changes in the airways, long-term immunosuppression, and previous exposure to antifungal drugs contribute to the higher prevalence of L. prolificans in these patient populations [102][103][104].
Disseminated infection is the most common pattern of L. prolificans infection reported, and is associated with very high mortality rate, as shown in our systematic review. Risk factors for dissemination include solid organ transplantation, HSCT, malignancies (especially hematologic), AIDS, neutropenia, and immunosuppressive therapy [1,8,105,106]. The primary location of the fungus, the degree of immunosuppression, and the speed of disease progression determine the clinical outcome. Primary location of the fungus, such as eyes, joint, bone, and skin plays an important role in clinical outcome, since resection of surgically amenable lesions is significantly associated with improved survival [105,107]. This comes in agreement with our results, since those patients who underwent surgery had higher survival rate. The most frequent clinical manifestations of disseminated disease include fever and CNS, heart and/or respiratory involvement, along with skin lesions, particularly numerous erythematous non-pruritic skin nodules with or without a necrotic center [1,7,44].
Several determinants of pathogenesis have a role in the manifestation of disease [100], associated with germination [108], biofilm formation [109], destruction of lung epithelial cells [109], and infiltration of blood vessels [110], resulting in widespread dissemination to distal organs [110]. Important molecules in the fungal cell wall that enhance fungal virulence include peptidorhamnomannan, glucosylceramide, and melanin [111]. The susceptibility of this fungus to innate immunity, particularly to neutrophils, may explain the high rate of prevalence in neutropenic patients [106]. Therefore, correction of neutropenia is of paramount importance, associated with a favorable outcome [26]. At the same time, a weak innate systemic response of microglial cells in the CNS explains the propensity of this fungus to invade and live in the CNS, a phenomenon known as neurotropism [112]. Detection of L. prolificans in clinical specimens relies principally on direct microscopic examination of fresh specimens or histopathologic analysis, together with culture on appropriate culture media [5]. Histopathologic examination can provide valuable evidence of invasive disease, but culture is necessary because different molds share the same characteristics under the microscope [5]. Direct microscopy and culture are the cornerstone of proven fungal infection [113]. A positive culture from the respiratory system in the absence of radiologic or endobronchial changes may indicate colonization [114]. Disseminated infection can be detected with blood cultures. Positive blood culture is rare in most molds, except those capable of angioinvasion with widespread dissemination, such as Scedosporium/Lomentospora and Fusarium species, and zygomycetes such as Rhizopus and Mucor [110] As shown in this systematic review, blood cultures were positive in 107 of 142 (75.3%) patients. However, their diagnostic utility is limited because most blood cultures become positive late in the course of the disease due to slow growth of the microorganism [1]. Molecular techniques, such as PCR, either panfungal or species-specific, followed by DNA sequencing, can detect invasive fungal infections directly from fresh and formalin-fixed paraffin-embedded (FFPE) material, but only in conjunction with histopathologic examination [115][116][117]. Several case reports have mentioned high serum 1, 3-beta-D-glucan (BDG) levels in patients with L. prolificans infection [51,80], while some other reports, mentioned low serum BDG levels [118]. Hence, although this panfungal biomarker (BDG) may be useful in diagnosis when invasive fungal infection is suspected [5], its clinical utility is controversial. Therefore, results should always be interpreted in conjunction with the other diagnostic methods mentioned above. Matrix-assisted laser desorption/ionization time-of-flight is rapid and reliable method for identifying L. prolificans, but is used by only few laboratories [119,120].
Treatment of L. prolificans infection is challenging because this fungus has intrinsic resistance to most antifungal agents used in clinical practice. The treatment strategy for disseminated disease includes a combination of surgical and antifungal therapy, as well as correction of underlying immune deficiencies [121]. Once invasive L. prolificans is suspected or confirmed, surgical removal of infected tissue should be initiated if feasible [121]. Current clinical practice guidelines recommend that first-line antifungal treatment with voriconazole and terbinafine plus or minus other antifungal agents over a period of at least 4 to 6 months is associated with a favorable outcome [121]. According to Jenks et al., combination therapy with voriconazole plus terbinafine may be associated with improved treatment outcomes compared with other antifungal regimens for the treatment of invasive L. prolificans infections [122]. Clinical evaluation, laboratory studies (inflammatory markers, microbiologic studies), and imaging should be reviewed frequently to assess respond to treatment. Frequency depends on the concomitant conditions, disease severity and initial response to treatment.
Inherent resistance to most available treatments raises the need for new classes of antifungal agents [123]. Olorofim, a key enzyme in the biosynthesis of pyrimidines, has the ability to inhibit dihydroorotate dehydrogenase [124]. It is currently in Phase IIB clinical trials for the treatment of invasive mold infections, including L. prolificans, in patients with limited treatment options [124]. The efficacy of olorofim has been demonstrated in in vitro studies and improved clinical outcomes have been observed in two case reports [124][125][126].
This study has several limitations. It was not possible to perform a meta-analysis because all data are based on case reports and small case series. The above limitations could have affected the quality of our findings and conclusions. However, by using the JBI critical appraisal checklist for each article included in our systematic review, we attempted to minimize the risk of bias and increase quality. The geographic distribution of publications that were included in our review probably reflects research and clinical interest rather than presence of the fungus only in these areas and environments. Finally, despite the high number of titles analyzed in our review, several studies on invasive infections by L. prolificans were excluded, as they did not fulfil inclusion criteria. Although excluded, these studies provide important clinical information on these infections [8,102,107,122].

Conclusions
Disseminated disease caused by L. prolificans is a rare infection with significant mortality, and should be suspected especially in immunocompromised and neutropenic patients. Early diagnosis and careful interpretation of culture results are important in the management of these patients. Novel antifungal agents and further exploration of therapeutic options are needed to improve the outcome of this highly fatal infection. Healthcare providers treating patients with disseminated fungal infection should be aware of this life-threatening pathogen.