Indoor Plumbing Drains Are Important Sources for Invasive Fusariosis in Patients with Hematological Disorders: Culture-Based and Metagenomic Analysis

Despite the advances in antifungal drugs, the number of invasive fusariosis (IF) has been increasing in patients with hematological disorders, especially hematopoietic stem cell transplantation (HSCT) patients. IF is still a severe infection and refractory to treat because Fusarium is naturally resistant to most of the antifungal drugs. Therefore, prior to infection, avoidance of contact with Fusarium would be critical in immunocompromised patients. However, little is known about the source of Fusarium infection. The purpose of this study is to investigate the epidemiology of IF in patients with hematological disorders in Japan and to find out the infectious source of Fusarium and the relationship between Fusarium species isolated from clinical samples and the ones from environment using culture-based and metagenomic methods.

In our center, a total of 99 clinically isolated Fusarium were stored and maintained. They were obtained from hospitals in 33 prefectures in Japan. 50 and 49 strains were recovered from IF patients and superficial fusariosis (SF) patients, respectively. In this study, we analyzed 42 IF cases which developed in patients with hematological disorders. The most common underlying disease was AML (35.7%), followed by ALL (23.8%). About 60% of the patients received HSCT, and most of them became infected with Fusarium in the early phase after HSCT (within eight weeks). This result indicated that IF infection mostly occurred in indoor environments.

As the next step, we performed the surveys in indoor environments such as air and plumbing drains in medical institutions and residences to figure out the source of infection. Few Fusarium species were collected from air samples. From the indoor air, we collected 142 filamentous fungi isolates. Only 2/142 strains (1.4%) were Fusarium species (Fusarium fujikuroi species complex 1, F. nisikadoi 1). In contrast, among the 72 drain port samples collected from 6 medical institutions (hematology wards, including bone marrow transplantation units, and ICU/NICU) and 15 residences, Fusarium species were positive at 26 (36.1%) sampling points. One hundred and eight filamentous fungi were isolated from the drain samples, and 29/108 isolates (27%) were Fusarium species. In details, 20 strains were Fusarium solani species complex (F. petroliphilum 7, F. keratoplasticum 4, F. sensu stricto 4, F. falciforme 1, others 4) and nine strains were Fusarium oxysporum species complex. Interestingly, the FSSC compositions of drain port samples were similar to those of IF samples from patients with hematological disorders and different from those of SF samples. In contrast, no Fusarium strains were detected in the places where the regular sink-cleaning was performed.

Likewise, the samples for the metagenomic analysis were obtained in the places where the culture samples were collected. DNA extraction from samples was performed by the PowerLyzer Powersoil Kit (QIAGEN, Hilden, Germany). Fungal ITS regions were amplified with modified ITS1F and ITS2 primer set and sequenced with Illumina Miseq platform. After filtering and denoising, we were able to analyze 8 air samples and 23 drain samples (10 culture-positive samples and 13 culture-negative samples). It is also revealed that a lot of Fusarium live indoor plumbing drains but few Fusarium spp. inhabit indoor air (less than 0.1%).

In summary, we investigate the epidemiology of IF in patients with hematological disorders in Japan and the distribution of Fusarium species in indoor environments. Our survey has demonstrated that a lot of Fusarium inhabits the indoor plumbing drains, not the indoor air using the culture-based and metagenomic methods. The similarity of FSSC distribution between the drain samples and causative species of IF cases indicated that the indoor plumbing drains would be potential sources of IF infection. We suggested that regular sink-cleaning was critical to prevent patients with hematological disorders from Fusarium infection.