Metagenomic Next-Generation Sequencing Contributes to the Early Diagnosis of Mixed Infections in Central Nervous System.

Central nervous system (CNS) infections represent a challenge due to the complexities associated with their diagnosis and treatment, resulting in a high incidence rate and mortality. Here, we presented a case of CNS mixed infection involving Candida and human cytomegalovirus (HCMV), successfully diagnosed through macrogenomic next-generation sequencing (mNGS) in China. A comprehensive review and discussion of previously reported cases were also provided. Our study emphasizes the critical role of early pathogen identification facilitated by mNGS, underscoring its significance. Notably, the integration of mNGS with traditional methods significantly enhances the diagnostic accuracy of CNS infections. This integrated approach has the potential to provide valuable insights for clinical practice, facilitating early diagnosis, allowing for treatment adjustments, and ultimately, improving the prognosis for patients with CNS infections.

Prevalence and Antifungal Susceptibility of Sporothrix species in Guangzhou, Southern China.

INTRODUCTION: Sporotrichosis is a subcutaneous and chronic infection caused by traumatic inoculation of pathogenic sporothrix species, usually infecting the skins and subcutaneous tissues of humans and animals. However, the lack of epidemiological data required further molecular identification to describe the distribution of this fungus in our region. In this study, forty-eight clinical sporothrix isolated from Sun Yat-Sen Memorial Hospital were classified, and the susceptibility of each strain to seven antifungal agents was determined. METHODS: Forty strains of S. globosa and eight strains of S. shenkshii were identified via colony morphology and PCR sequencing of calmodulin gene. RESULTS: Antifungal susceptibility tests of the mycelial phase in vitro showed terbinafine (TRB) and luliconazole (LULI) were the most effective, followed by itraconazole (ITZ) and amphotericin B (AMB). By contrast, voriconazole (VCZ), 5-flucytosine (5FC) and fluconazole (FCZ) have low efficacy with high MIC. CONCLUSION: Our results showed a predominantly S. globosa infection trend in southern China. Simultaneously, sporothrix is sensitive to TRB, LULI, ITZ and AMB whereas resistant to FCZ. This study firstly reports antifungal sensitivity test in vitro and epidemiological correlation analysis of sporothrix in southern China, and also the first time to find that sporothrix is sensitive to LULI.

Combination therapy with itraconazole and terbinafine for phaeohyphomycosis caused by Exophiala spinifera: A case report and literature review.

Exophiala spinifera is a rare dematiaceous fungus causing cutaneous, subcutaneous and disseminated phaeohyphomycosis (PHM). Standard antifungal therapy for PHM is still uncertain. Here, we report a case of a Chinese male with PHM caused by E. spinifera, who received significant clinical improvement after the treatment with oral itraconazole and terbinafine. With the aim of evaluating the antifungal therapy for PHM caused by E. spinifera, a detailed review was performed.

Epidemiology and Clinical Findings of Tinea Capitis: A 23-Year Retrospective, Single-Center Study in Guangzhou, China.

BACKGROUND: Tinea capitis (TC) is one of the most common public health concerns due to its high incidence in preadolescent children. The epidemiological and clinical characteristics of TC vary depending on geographical regions and have changed over the past decades. OBJECTIVES: This study aimed to identify epidemiological changes in recent decades, including the prevalence and clinical and mycological characteristics of TC in southern China. METHODS: We conducted a retrospective study at the Department of Dermatology of Sun Yat-sen Memorial Hospital, Sun Yat-sen University from June 1997 to August 2020. RESULTS: We retrospectively evaluated 401 TC patients. Of these, 157 patients (39.2%) were preschool children aged 3-7 years and the majority were males. However, the prevalence in children under 3 years old is on the rise (from 19.67% during 1997-2010 to 32.49% during 2011-2020). Grey patches were the most common clinical pattern and mostly occurred in children (71.3%), while the proportion of grey patches and black dots was almost the same in adults. Although Microsporum canis (76%) was the most common causative organism, the number of the T. mentagrophytes complex, as a zoophilic fungus, has increased more than that of the anthropophilic fungi T. violaceum in the recent decade. There was a significant difference in the portion of sex among different age groups, and the gender difference was more notable in the adult group, which showed that the TC prevalence in females was 9 times that in males. In males, M. canis and the T. mentagrophytes complex were the two most common causative fungi, while M. canis and T. violaceum were the two most common causative fungi in females. Additionally, approximately 61.7% of black dot TCs occurred in females. For treatment, oral antifungal therapeutics were widely used in most patients with different treatment durations, although without a significant difference in efficacy (P = 0.106). CONCLUSIONS: In the last decade, the prevalence of TC in children under 3 years old increased, and boys dramatically outnumbered girls. In adults, the TC prevalence in females is nine times that in males, and most TCs occurring in females are presented as black dots. Moreover, the zoophilic T. mentagrophytes complex has replaced T. violaceum and is now the second most prevalent organism, followed by M. canis of TC.

Deep learning-based diagnosis models for onychomycosis in dermoscopy.

BACKGROUND: Onychomycosis is a common disease. Emerging noninvasive, real-time techniques such as dermoscopy and deep convolutional neural networks have been proposed for the diagnosis of onychomycosis. However, deep learning application in dermoscopic images has not been reported. OBJECTIVES: To explore the establishment of deep learning-based diagnostic models for onychomycosis in dermoscopy to improve the diagnostic efficiency and accuracy. METHODS: We evaluated the dermoscopic patterns of onychomycosis diagnosed at Sun Yat-sen Memorial Hospital, Guangzhou, China, from May 2019 to February 2021 and included nail psoriasis and traumatic onychodystrophy as control groups. Based on the dermoscopic images and the characteristic dermoscopic patterns of onychomycosis, we gain the faster region-based convolutional neural networks to distinguish between nail disorder and normal nail, onychomycosis and non-mycological nail disorder (nail psoriasis and traumatic onychodystrophy). The diagnostic performance is compared between deep learning-based diagnosis models and dermatologists. RESULTS: All of 1,155 dermoscopic images were collected, including onychomycosis (603 images), nail psoriasis (221 images), traumatic onychodystrophy (104 images) and normal cases (227 images). Statistical analyses revealed subungual keratosis, distal irregular termination, longitudinal striae, jagged edge, and marble-like turbid area, and cone-shaped keratosis were of high specificity (>82%) for onychomycosis diagnosis. The deep learning-based diagnosis models (ensemble model) showed test accuracy /specificity/ sensitivity /Youden index of (95.7%/98.8%/82.1%/0.809) and (87.5%/93.0%/78.5%/0.715) for nail disorder and onychomycosis. The diagnostic performance for onychomycosis using ensemble model was superior to 54 dermatologists. CONCLUSIONS: Our study demonstrated that onychomycosis had distinctive dermoscopic patterns, compared with nail psoriasis and traumatic onychodystrophy. The deep learning-based diagnosis models showed a diagnostic accuracy of onychomycosis, superior to dermatologists.

Comparison of a fractional 2940-nm Er:YAG laser and 5% amorolfine lacquer combination therapy versus a 5% amorolfine lacquer monotherapy for the treatment of onychomycosis: a randomized controlled trial.

Onychomycosis is a fungal infection of the nail. The aim of this randomized controlled clinical trial was to compare the efficacy of 2940-nm Er:YAG laser treatment combined with a 5% amorolfine lacquer versus amorolfine monotherapy for treating onychomycosis. In this study, patients with onychomycosis of the great toenail were randomly assigned to a combination therapy group and a monotherapy group. In the combination therapy group, the included toenails were treated with a fractional 2940-nm Er:YAG laser at weeks 1, 2, 3, 4, 8, and 12, combined with a 5% amorolfine lacquer twice a week for 12 weeks, while in the monotherapy group, the included toenails were treated with only a 5% amorolfine lacquer twice a week for 12 weeks. The onychomycosis severity index (OSI) score and the mycological clearance rate (MCR) of the included toenails were assessed at baseline, week 12, and week 24. At weeks 12 and 24, the great toenails with mild and moderate onychomycosis in the combination therapy group showed obvious improvement and a greater decrease in OSI than those in the monotherapy group. At week 24, the toenails with mild and moderate onychomycosis in the combination therapy group also showed a better MCR. For the toenails with severe onychomycosis, little improvement was observed in either group at week 12 or week 24. In conclusion, fractional 2940-nm Er:YAG laser treatment combined with a 5% amorolfine lacquer is more effective than amorolfine monotherapy in short-term improvement of onychomycosis.

Melanization of a meristematic mutant of Fonsecaea monophora increase the pathogenesis in a BALB/c mice infection model.

The role of melanin in agents of chromoblastomycosis in vivo still remains unclear. In this study, we addressed the question in a BALB/c mice infection model by using an albino mutant, which generated from a melanized meristematic mutant of F. monophora. The most severe clinical manifestations of infected mice were observed at 10-25 dpi (day post infection) and 7-15 dpi for melanized and albino strain, respectively. Histopathologic examination were similar in both groups at 15 dpi (acute infection phase), but not at 30 dpi (sustained infection phase) and 45 dpi (recovery phase). Sclerotic body could be revealed in melanized strain infection group compare with albino strain infection group at 45 dpi. We found significantly elevated of TH2 cytokines in melanized strain infected group at 15 dpi, while increased expression level of TH1 and TH17 cytokines in albino strain infection group at 15 and 30 dpi. In conclusion, the present data addressed our speculation that melanization of this meristematic mutant of F. monophora could increase the pathogenesis in vivo. The inhibition of TH1 and TH17, exacerbated TH2 ability of melanized F. monophora is the key to escape the host immune system at the initial recognition and persistence in BALB/c mice.

Whole blood Nested PCR and Real-time PCR amplification of Talaromyces marneffei specific DNA for diagnosis.

Talaromyces marneffei is a dimorphic pathogenic fungus, which is a life-threatening invasive mycosis in the immunocompromised host. Prompt diagnosis of T. marneffei infection remains difficult although there has been progress in attempts to expedite the diagnosis of this infection. We previously demonstrated the value of nested polymerase chain reaction (PCR) to detect T. marneffei in paraffin embedded tissue samples with high sensitivity and specificity. In this study, this assay was used to detect the DNA of T. marneffei in whole blood samples. Real-time PCR assay was also evaluated to identify T. marneffei in the same samples. Twenty out of 30 whole blood samples (67%) collected from 23 patients were found positive by using the nested PCR assay, while 23/30 (77%) samples were found positive by using the real-time PCR assay. In order to express accurately the fungal loads, we used a normalized linearized plasmid as an internal control for real-time PCR. The assay results were correlated as the initial quantity (copies/µl) with fungal burden. These data indicate that combination of nested PCR and real-time PCR assay provides an attractive alternative for identification of T. marneffei DNA in whole blood samples of HIV-infected patients.

Combination therapy for onychomycosis using a fractional 2940-nm Er:YAG laser and 5 % amorolfine lacquer.

Onychomycosis remains difficult to cure by traditional methods. The aim of this study was to evaluate the efficacy of combination therapy with a fractional erbium yttrium aluminum garnet (Er:YAG) laser and 5 % amorolfine lacquer on onychomycosis. Nine patients with bilateral nails affected by distal and lateral subungual onychomycosis were included. The bilateral nails of each patient were divided into two groups. The 20 affected nails on one side of each patient as group 1 were treated with a fractional Er:YAG laser once a week and 5 % amorolfine lacquer twice weekly, while the 20 nails on the symmetrical side of each patient as group 2 were treated with amorolfine lacquer only. The laser treatment was conducted at weeks 1, 2, 3, 4, 8, and 12 in group 1. The clinical improvement, onychomycosis severity index (OSI), maximum linear clear nail growth (MLCNG), and mycological cure rate were evaluated. At week 24, 18 of 20 (90 %) nails in group 1 had achieved obvious clinical responses. The mean OSI score showed a significant decrease (5.24) and the average MLCNG was 3.1 mm in group 1. At week 24, 15 of 20 (75 %) nails achieved a negative mycological examination in group 1, compared with four of 20 (20 %) nails in group 2. The treatments were well-tolerated by most patients. This clinical study suggests that combination therapy of a fractional 2940-nm Er:YAG laser and 5 % amorolfine lacquer is an effective, safe, and convenient treatment method for onychomycosis.

Epidemiology of Superficial Fungal Infections in Guangdong, Southern China: A Retrospective Study from 2004 to 2014.

Superficial fungal infections are common worldwide; however, the distribution of pathogenic species varies among geographical areas and changes over time. This study aimed to determine the epidemiologic profile of superficial fungal infections during 2004-2014 in Guangzhou, Southern China. Data regarding the superficial mycoses from outpatients and inpatients in our hospital were recorded and analyzed. From the 3367 patients that were enrolled in the study, 3385 samples were collected from skin, hair and nail lesions. Of the 697 positive cultures, dermatophytes were the most prevalent isolates (84.36 %), followed by yeasts (14.92 %) and non-dermatophyte molds (0.72 %). Trichophyton rubrum (56.24 %) was the most common dermatophyte isolated from cases of tinea unguium (83.92 %), tinea pedis (71.19 %), tinea cruris (91.66 %), tinea corporis (91.81 %) and tinea manuum (65.00 %). Trichophyton mentagrophytes (13.35 %) and Microsporum canis (10.19 %) were the predominant species associated with cases of tinea faciei (54.55 %) and tinea capitis (54.13 %), respectively. Yeasts and molds were identified primarily from other cases of superficial fungal infections. In conclusion, when compared to previous studies in the same area, the epidemiology of superficial mycoses in Guangdong did not significantly change from 2004 to 2014. The prevalence of causative agents and the spectrum of superficial fungal infections, particularly tinea caused by dermatophyte infection, are similar to reports from several specific regions in China and Europe, whereas increasing incidences of Trichophyton mentagrophytes and Microsporum canis occurred in Guangdong, China.

Role of Dectin-1 in immune response of macrophages induced by Fonsecaea monophora wild strain and melanin-deficient mutant strain.

Chromoblastomycosis is a chronic granulomatous subcutaneous fungal disease caused mainly by Fonsecaea monophora in southern China. Melanin is an important virulence factor in wild strain (Mel+), and the strains lack of the polyketide synthase gene is a melanin-deficient mutant strain (Mel-). We investigated the effect of melanin in F. monophora on Dectin-1 receptor-mediated immune responses in macrophages. Conidia and tiny hyphae of Mel+ and Mel- were co-cultured with THP-1 macrophages expressing normal or low levels of Dectin-1. Compare the killing rate, phagocytosis rate, and expression levels of the inflammatory cytokines tumour necrosis factor-α, interleukin-1ß, interleukin-6, and nitric oxide in each group. The results showed that the killing rate, phagocytosis rate, and pro-inflammatory factor levels of Mel+ infected macrophages with normal expression of Dectin-1 were lower than those of Mel-. And the knockdown of Dectin-1 inhibited the phagocytic rate, killing rate, and proinflammatory factor expression in macrophages infected with Mel+ and Mel-. And there was no significant difference in the above indexes between Mel+ and Mel- groups in Dectin-1 knockdown macrophages. In summary, the study reveals that melanin of F. monophora inhibits the immune response effect of the host by hindering its binding to Dectin-1 on the surface of macrophage, which may lead to persistent fungal infections.

Fungal Spectrum and Susceptibility Against Nine Antifungal Agents in 525 Deep Fungal Infected Cases.

Background: Deep fungal infection has become an important cause of infection and death in hospitalized patients, and this has worsened with increasing antifungal drug resistance. Objective: A 3-year retrospective study was conducted to investigate the clinical characteristics, pathogen spectrum, and drug resistance of deep fungal infection in a regional hospital of Guangzhou, China. Methods: Non-duplicate fungi isolates recovered from blood and other sterile body fluids of in-patients of the clinical department were identified using biochemical tests of pure culture with the API20C AUX and CHROMagar medium. Antifungal susceptibilities were determined by Sensititre YeastOne® panel trays. Results: In this study, 525 patients (283 female, 242 male) with deep fungal infection were included, half of them were elderly patients (≥60 years) (54.67%, n=286). A total of 605 non-repetitive fungi were finally isolated from sterile samples, of which urine specimens accounted for 66.12% (n=400). Surgery, ICU, and internal medicine were the top three departments that fungi were frequently detected. The mainly isolated fungal species were Candida albicans (43.97%, n=266), Candida glabrata (20.00%, n=121), and Candida tropicalis (17.02%, n=103), which contributed to over 80% of fungal infection. The susceptibility of the Candida spp. to echinocandins, 5-fluorocytosine, and amphotericin B remained above 95%, while C. glabrata and C. tropicalis to itraconazole were about 95%, and the dose-dependent susceptibility of C. glabrata to fluconazole was more than 90%. The echinocandins had no antifungal activity against Trichosporon asahi in vitro (MIC90>8 µg/mL), but azole drugs were good, especially voriconazole and itraconazole (MIC90 = 0.25 µg/mL). Conclusion: The main causative agents of fungal infection were still the genus of Candida. Echinocandins were the first choice for clinical therapy of Candida infection, followed with 5-fluorocytosine and amphotericin B. Azole antifungal agents should be used with caution in Candida glabrata and Candida tropicalis infections.

Evaluating city road dust emission characteristics with a dynamic method: A case study in Luoyang, China.

Road dust, a significant contributor to non-exhaust particulate matter emissions in urban transport, poses considerable health risks, necessitating accurate and high-resolution data for effective control. The traditional AP-42 method offers data on point-specific dust emissions, while vehicle-based testing ascertains the relative emission intensity in the road network. However, a clear mathematical relationship between these measurements has been elusive, limiting efficiency in emission control. By integrating the On-board Conventional Pollutant Monitoring System with the AP-42 method, we devised a dynamic link between the concentration of particles in vehicle plumes and actual road dust emissions. This relationship is substantiated by a notable correlation (R2 = 0.91) between our emission factors and those calculated using the AP-42 method. Significant variations emerged in dust emission factors across road types, with changes between -30.1 % to +57.79 % from the average (0.05 g·vehicle-1·km-1), in tandem with traffic flow fluctuations of approximately ±90 %. Meteorological factors, except for continuous rainfall, showed minimal impact on dust emissions. However, our findings revealed a significant underestimation (58.87 %) of road dust PM10 emissions by the AP-42 method. Intriguingly, we found that short-range emission hotspots substantially contribute to total emissions, suggesting a potential 50 % reduction by controlling merely 8.8 % ± 2.5 % of the total road length. Our research elucidates the interplay between road dust emissions, road types, and human activities. The application of a dynamic, high-resolution assessment method enhances our understanding of the impacts of road dust on urban particulate pollution, allows accurate hotspot identification, and aids in developing efficacious strategies for air quality enhancement.

Molecular Characteristics of Regional Chromoblastomycosis in Guangdong, China: Epidemiological, Clinical, Antifungal Susceptibility, and Serum Cytokine Profiles of 45 Cases.

Chromoblastomycosis (CBM) is a chronic disease caused by several species of dematiaceous fungi. In this study, a regional collection of 45 CBM cases was conducted in Guangdong, China, a hyper-endemic area of CBM. Epidemiology findings indicated that the mean age of cases was 61.38 ± 11.20 years, long duration ranged from 3 months to 30 years, and the gender ratio of male to female was 4.6:1. Thirteen cases (29%) declared underlying diseases. Verrucous form was the most common clinical manifestation (n = 19, 42%). Forty-five corresponding clinical strains were isolated, and 28 of them (62%) were identified as F. monophora; the remaining 17 (38%) were identified as F. nubica through ITS rDNA sequence analysis. Antifungal susceptibility tests in vitro showed low MICs in azoles (PCZ 0.015-0.25 µg/ml, VCZ 0.015-0.5 µg/ml, and ITZ 0.03-0.5 µg/ml) and TRB (0.015-1 µg/ml). Itraconazole combined with terbinafine was the main therapeutic strategy used for 31 of 45 cases, and 68% (n = 21) of them improved or were cured. Cytokine profile assays indicated upregulation of IL-4, IL-7, IL-15, IL-11, and IL-17, while downregulation of IL-1RA, MIP-1ß, IL-8, and IL-16 compared to healthy donors (p < 0.05). The abnormal cytokine profiles indicated impaired immune response to eliminate fungus in CBM cases, which probably contributed to the chronic duration of this disease. In conclusion, we investigated the molecular epidemiological, clinical, and laboratory characteristics of CBM in Guangdong, China, which may assist further clinical therapy, as well as fundamental pathogenesis studies of CBM.

Deletion of pksA attenuates the melanogenesis, growth and sporulation ability and causes increased sensitivity to stress response and antifungal drugs in the human pathogenic fungus Fonsecaea monophora.

Fonsecaea monophora, which is very similar to Fonsecaea pedrosoi in morphological features, has been commonly misdiagnosed as F. pedrosoi. Like F. pedrosoi, F. monophora has been also identified as a predominant pathogen of Chromoblastomycosis (CBM). Melanin has been recognized as a virulence factor in several fungi, however, it is still largely unknown about the biological role of melanin and how melanin is synthesized in F. monophora. In this study, we identified two putative polyketide synthase genes (pks), AYO21_03016 (pksA) and AYO21_10638, by searching against the genome of F. monophora. AYO21_03016 and AYO21_10638 were further targeted disrupted by Agrobacterium tumefaciens-mediated transformation (ATMT). We discovered that pksA gene was the major polyketide synthase required for melanin synthesis in F. monophora, rather than AYO21_10638. Phenotypic analysis showed that, knocking out of the pksA gene attenuated melanogenesis, growth rate, sporulation ability and virulence of F. monophora, as compared with wild-type and complementation strain (pksA-C). Furthermore, the ΔpksA mutant was confirmed to be more sensitive to the oxidative stress, extreme pH environment, and antifungal drugs including itraconazole (ITC), terbinafine (TER), and amphotericin B (AMB). Taken together, these findings enabled us to comprehend the role of pksA in regulating DHN-melanin pathway and its effect on the biological function of F. monophora.

An optimized Agrobacterium tumefaciens-mediated transformation system for random insertional mutagenesis in Fonsecaea monophora.

Chromoblastomycosis (CBM) is a chronic cutaneous or subcutaneous mycosis that is prevalent worldwide. Though CBM tends not to be fatal, it is difficult to treat and complications can include chronic, marked lesions, lymphatic damage, and neoplastic transformation. Fonsecaea monophora, as a new species segregated from Fonsecaea pedrosoi, is the predominant causative pathogen of CBM in southern China. However, research about F. monophora has been limited, which may be due to a lack of an effective genetic manipulation system for F. monophora. In this study, we successfully established a random insertional mutagenesis system by Agrobacterium tumefaciens-mediated transformation (ATMT) in F. monophora for the first time. In order to improve the efficiency of ATMT, various co-culture conditions were optimized, including: acetosyringone (AS) concentrations, co-culture duration, ratio of bacteria to conidia, and the A. tumefaciens strains. In addition, thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR) was performed to identify the transferred DNA (T-DNA) flanking sequences of the F. monophora transformants. The valuable transformants obtained in this study will be used for research in the future.

Cutaneous fusariosis caused by Fusarium lichenicola in a child with hyper-immunoglobulin E syndrome.

Fusariosis is the second most common mold infection after aspergillosis, and keratomycosis is the most encountered implantation infection. Here, we report a case of a 4-year-old Han Chinese girl presenting with an itchy mass on her right face of almost 2 years' duration. Direct smear of the lesion sample was positive for fungal hyphae. Biopsy of the lesion showed many fungal hyphae in the epidermis and dermis. The pathogen was identified as Fusarium lichenicola by molecular sequencing and phylogenetic analysis based on the TEF-1α gene. Whole-exome sequencing analysis using her peripheral blood revealed a heterozygous mutation in the STAT3 gene, which is related to autosomal dominant hyper-immunoglobulin E syndrome (AD-HIES). The lesion improved following treatment with i.v. and intralesional amphotericin B, oral voriconazole and topical luliconazole cream. To our knowledge, this is the second reported case of a special localized cutaneous lesion caused by Fusarium species in a child with AD-HIES. Both cases suggest that STAT3 deficiency may increase susceptibility to fusariosis.

Indoor wet cells as a habitat for melanized fungi, opportunistic pathogens on humans and other vertebrates.

Indoor wet cells serve as an environmental reservoir for a wide diversity of melanized fungi. A total of 313 melanized fungi were isolated at five locations in Guangzhou, China. Internal transcribed spacer (rDNA ITS) sequencing showed a preponderance of 27 species belonging to 10 genera; 64.22% (n = 201) were known as human opportunists in the orders Chaetothyriales and Venturiales, potentially causing cutaneous and sometimes deep infections. Knufia epidermidis was the most frequently encountered species in bathrooms (n = 26), while in kitchens Ochroconis musae (n = 14), Phialophora oxyspora (n = 12) and P. europaea (n = 10) were prevalent. Since the majority of species isolated are common agents of cutaneous infections and are rarely encountered in the natural environment, it is hypothesized that indoor facilities explain the previously enigmatic sources of infection by these organisms.