Endemic Fungal Infections in Solid Organ Transplant Recipients

Abstract

Histoplasmosis, blastomycosis and coccidioidomycosis, are endemic mycoses that are prevalent in specific geographic regions. The environment is the main source for exposure to these fungi, with the respiratory tract serving as the primary portal of entry into the human body. The fungi associated with these diseases are thermally dimorphic; they exist as a mould form in the environment or in the laboratory at 25°C and convert to yeast form in tissues or at 37°C. Symptomatic disease occurs in both the immunocompetent and immunocompromised host with the severity of infection correlating with underlying immune status. Recently reports of endemic fungal infections occurring in solid organ transplant recipients have been increasing (1, 2). Though the true incidence of these infections among this population is unknown, estimates suggest it is <5% (3, 4). The focal geographic distribution of the endemic fungi and indolent symptoms of infection frequently lead to diagnostic delays and contribute to increased morbidity and mortality (4, 5). Knowledge of the epidemiology, pathogenesis, clinical manifestations, diagnostic methodologies and therapy will enable clinicians to more effectively identify and manage transplant recipients with endemic mycoses. Epidemiology and pathogenesis: Blastomycosis refers to disease caused by the fungus, Blastomyces dermatitidis, and occurs more often in persons living in the midwestern, southeastern and south central United States, particularly along the Ohio-Mississippi River Valley (6). B. dermatitidis is also found in the soil of northern New York and Canadian provinces that border the Great Lakes and St. Lawrence Seaway. Recent studies have shown an increase in the incidence of blastomycosis in some of these endemic regions (5). The majority of cases of blastomycosis following organ transplantation have occurred in patients residing in endemic areas (1). Historically, blastomycosis has been a disease that affects predominantly men with outdoor occupations or recreational activities involving soil exposure, although a significant number of individuals have no apparent source for infection (6, 7). Blastomycosis has also long been considered a disease of the immunocompetent host. However, it is associated with severe pneumonia or disseminated infection in the immunocompromised host, particularly in patients with diabetes, HIV or those receiving chronic corticosteroids or cytotoxic chemotherapy (8). Unlike coccidioidomycosis or histoplasmosis, blastomycosis has been described infrequently as an opportunistic pathogen following solid organ transplantation. In one review, the cumulative incidence posttransplant was only 0.14% during a 16-year period (1). Reports of blastomycosis following renal, cardiac, hepatic and lung transplantation have been published with disease onset ranging from 1 week to 20 years posttransplant (1, 8, 9). Blastomycosis in this population may result from primary infection, reactivation of latent disease or conversion of subclinical infection to symptomatic disease after organ transplantation (1). To date, there are no reports of donor transmission of B. dermatitidis. Infection with B. dermatitidis results from inhalation of fungal spores into pulmonary alveoli where, once deposited, they convert to yeast form. Cell-mediated immunity is an important host defense limiting progression of B. dermatitidis infection in the lungs. If cellular immune responses are impaired, pneumonia or extrapulmonary dissemination may develop. Not surprisingly, the majority of transplant recipients who develop blastomycosis are taking prednisone as part of their immunosuppressive regimen (1, 8, 9). Posttransplant blastomycosis has also been described in patients taking cyclosporine, tacrolimus or mycophenolate, often in combination with prednisone, as well as alemtuzumab (1). Cytomegalovirus (CMV) infection can also impair cellular immune defenses and, although its exact role is unclear, in one study one-third of patients with posttransplant blastomycosis were co-infected with CMV (1). There are no data to suggest that acute rejection increases the risk for blastomycosis (1). Although the lungs are the most common site for initial infection, blastomycosis arising from primary cutaneous inoculation is also described (10). Clinical presentation: Pneumonia with or without extrapulmonary dissemination is the most common presentation of blastomycosis in solid organ transplant recipients (1, 8, 9). Although the time from surgery to development of blastomycosis is variable, in one review the median onset was 2 years posttransplant (1). Generally, the spectrum of pulmonary infection caused by B. dermatitidis ranges from subclinical disease to acute or chronic pneumonia (11). Acute pulmonary blastomycosis is a flu-like illness, which develops 30–45 days after initial infection. Typical symptoms include fever, chills, arthralgias and productive cough with an accompanying alveolar or lobar infiltrate on chest radiography. In solid organ transplant recipients the most common presenting symptoms were fever and cough (1). These symptoms are not specific for blastomycosis and, not uncommonly, patients may be misdiagnosed with bacterial pneumonia. Radiographic findings in transplant patients include lobar or interstitial infiltrates, a reticulonodular pattern with mediastinal adenopathy or lung cavities (9). A subset of individuals with pulmonary blastomycosis develop fulminant multilobar pneumonia and rapid progression to the adult respiratory distress syndrome (ARDS) and respiratory failure (12). In patients who underwent solid organ transplantation, diffuse bilateral pneumonia was the most common radiographic finding; 78% developed respiratory failure and ARDS complicated 67% of cases. The majority of patients that developed ARDS died (1). Chronic pulmonary blastomycosis may follow acute infection with more prolonged symptoms such as fever, night sweats, anorexia, weight loss, productive cough, pleurisy and occasional hemoptysis. Chest radiography or a computed tomography (CT) scan may show a mass-like infiltrate or cavitary pneumonia mimicking tuberculosis or malignancy (6). However, in our experience, time from symptom onset to diagnosis of blastomycosis in organ transplant recipients was shorter (median 1.5 months; range 1–2 months) compared with nontransplant patients (median 4.5 months, range 12 days–18 months), perhaps owing to more severe disease necessitating earlier hospitalization and diagnostic testing (5, unpublished data). While blastomycosis usually remains localized to the lungs, 25–40% of those infected will develop extrapulmonary dissemination manifested by cutaneous, osteo-articular, genitourinary or central nervous system (CNS) disease (6). Disseminated blastomycosis occurs frequently in immunosuppressed individuals, such as organ transplant recipients and those infected with HIV (1, 13). In solid organ transplant patients, disseminated disease was observed in 36–50%, with skin being the most common site of involvement outside the lungs (1, 8, 9). CNS blastomycosis appears to be rare in the setting of organ transplantation; CNS involvement was documented in a renal transplant recipient in one report (8) but was not observed in a review of 11 patients (1). Diagnosis: A presumptive diagnosis of blastomycosis is made by identifying the organism in sputum, bronchoalveolar lavage (BAL) fluid or tissue specimens; growth in culture confirms the diagnosis (11). In one study of solid organ transplant patients, culture of sputum or BAL fluid was 100% sensitive for diagnosing pulmonary blastomycosis (1). Alternatively other sites of involvement, such as skin, bone, synovial fluid, brain tissue or cerebrospinal fluid (CSF) may be sampled for histopathologic examination and culture. The characteristic fungal forms seen on direct examination are large (8–15 μm), broad-based budding yeast. A potassium hydroxide (KOH) wet mount or special fungal stains such as Gomori-methenamine silver (GMS) 0r periodic acid-Schiff (PAS), may enhance visualization of B. dermatitidis in body fluids or tissue. Microabscesses and noncaseating granulomas are often observed on histopathology since the initial inflammatory response to B. dermatitidis is both neutrophilic and cell-mediated. The urine Histoplasma antigen assay has a high degree of cross-reactivity with Blastomyces antigen, 63% in one report, and may be used to make a presumptive diagnosis while awaiting histopathologic or culture confirmation (14). An assay for detection of Blastomyces antigen in urine, blood and other body fluids has recently become available (15). In patients with blastomycosis, sensitivity and specificity of this assay was 92 and 79%, respectively; cross-reactivity occurred in 96% of patients with histoplasmosis (15). The utility of this test has not been established in solid organ transplant recipients. Currently available serologic tests lack sensitivity and are not useful for diagnosis of blastomycosis at this time. Treatment: Although there are no specific recommendations for management of blastomycosis in solid organ transplant recipients, treatment follows recently published guidelines (Table 1) (16). All immunocompromised individuals require treatment and since these patients are more likely to present with severe pulmonary or disseminated infection, amphotericin B is recommended as first line therapy (III). A lipid formulation, such as liposomal amphotericin B or amphotericin B lipid complex, is preferred because of the reduced potential for nephrotoxicity (16). Amphotericin B is administered for the first 1–2 weeks until clinical improvement is demonstrated at which time transition to oral itraconazole may be acceptable (III) (16). Liposomal amphotericin B is recommended for infection involving the CNS but a more prolonged duration of therapy is given, generally 4–6 weeks, followed by oral itraconazole, fluconazole or voriconazole (III) (16). In some patients with mild pulmonary infection, oral itraconazole may be given as initial therapy but close clinical monitoring is warranted (III). Fluconazole appears to be less effective for blastomycosis (II-1) and should only be used as second line therapy or in high doses for prolonged treatment of CNS infection (III) (16, 17). There are less clinical data with the newer azoles, voriconazole and posaconazole, although in vitro activity has been demonstrated and oral voriconazole may be an option for prolonged therapy of CNS blastomycosis (1, 16, 18-20). The echinocandins, caspofungin, micafungin and anidulafungin, have intermediate to poor in vitro activity against B. dermatitidis and should not be prescribed (19, 20). The duration of treatment is generally 12 months with resolution of symptoms and signs of infection (III). Consideration may be given to more prolonged treatment courses for immunosuppressed individuals, such as organ transplant recipients, although conclusive data are lacking (III) (16). Relapse of blastomycosis has been reported rarely; more recent data and our experience, suggest that relapse of blastomycosis is uncommon after therapy and evidence of cure. In a retrospective study of blastomycosis in solid organ transplant patients, no suppressive antifungal therapy was given following initial treatment and no infection relapse was observed during a median 47 month observation period (1). Pretransplant evaluation: There is no sensitive or specific serologic assay available to diagnose previous exposure to Blastomyces or active disease. Careful screening for active infection should be a part of the pretransplant evaluation of patients who live in areas where Blastomyces is prevalent. There have been no trials of targeted antifungal prophylaxis for prevention of blastomycosis in organ transplant recipients who reside in endemic regions. At this time primary or secondary antifungal prophylaxis for blastomycosis following solid organ transplantation is not recommended (III). Epidemiology and pathogenesis: Coccidioides species are fungi that thrive in the arid, desert soil of the southwestern United States, particularly the San Joaquin Valley and Sonoran desert of southern California, Arizona and northern Mexico (21, 22). Other regions of endemicity include New Mexico, western Texas and parts of Central and South America. Nonendemic coccidioidomycosis refers to primary or reactivation disease that develops in individuals after return from an endemic location or in those without a history of travel to an endemic area. In some cases, exposure to Coccidioides occurs when spores are carried to distant locations on fomites or on the surfaces of produce or textiles exported from endemic regions (23). Two species of Coccidioides have been identified: C. immitis is associated with infection acquired in California and C. posadasii with infection acquired outside of California, such as Arizona and New Mexico (24). Coccidioides spores gain entry into the body when aerosolized from soil and inhaled into the lungs (25). Increased infection rates have been observed after rainy seasons, dust storms or earthquakes, which disrupt soil and enhance the spread of spores. Coccidioides is highly infectious; a single inhaled spore may produce infection (26). Inhaled spores deposit in pulmonary alveoli where they convert to yeast form and enlarge into spherules containing endospores. These spherules then rupture releasing endospores into surrounding tissues. The large fungal structures of Coccidioides resist phagocytosis by neutrophils and macrophages; resolution of infection depends ultimately on T-cell immune responses (25). Persons with cell-mediated immune defects associated with organ transplantation or HIV infection may develop progressive primary infection or reactivation of latent disease. Coccidioidomycosis has been described following lung, kidney, heart and liver transplantation with an incidence of 3–9% in endemic regions (27-30). The majority of these infections are diagnosed within the first year posttransplant. In one review, 50% of individuals who developed posttransplant Coccidioides infection did so within 3 months of surgery and 70% within one year (31). Other risk factors for Coccidioides infection in the transplant population include treatment of acute rejection and prior history of coccidioidomycosis or positive pretransplant serologies (31). It is unclear whether concomitant immunosuppressing conditions such as diabetes or CMV infection further increase the risk for posttransplant coccidioidomycosis. Donor transmission of Coccidioides, often manifesting within 2 weeks posttransplant, has also been described (32, 33). In these cases, infection was widely disseminated and rapidly fatal. Clinical presentation: A wide range of clinical manifestations of Coccidioides infection have been observed in solid organ transplant recipients, from asymptomatic seroconversion to widespread dissemination with multiorgan failure and shock (30). However, unlike immunocompetent hosts in whom infection is often mild and self-limited, organ transplant patients are more likely to develop severe pneumonia and disseminated infection (30, 31). The most common symptoms of pulmonary cocidioidomycosis are fever, chills, night sweats, cough, dyspnea and pleurisy (30, 34). Radiographic findings are varied and may consist of lobar consolidation, pulmonary nodules, mass-like lesions, interstitial infiltrates or cavitary disease (30, 31). Pulmonary coccidiodomycosis can progress to severe pneumonia with multilobar involvement, ARDS and respiratory failure, particularly in the setting of immunosuppression (25). In the general population disseminated coccidioidomycosis is rare and develops in less than 1% of immunocompetent individuals (25). However in one review of coccidioidomycosis following renal transplantation, 75% of patients presented with disseminated disease and mortality was 63% (27). Additional risks for extrapulmonary dissemination are male gender, African, Filipino or Native American ancestry, pregnancy and other forms of immunosuppression (21, 30). It is unclear whether these factors pose any additional risk for dissemination of Coccidioides in solid organ transplant recipients. Extrapulmonary infection usually manifests as cutaneous, osteo-articular or meningeal disease. Widespread dissemination with multiorgan involvement, including graft infection, has been observed in patients following organ transplantation (27, 30, 31). CNS Coccidioides infection, usually presenting as meningitis with headache or altered mentation, has been reported in organ transplant recipients and may be fatal (31, 35). Diagnosis: Culture of sputum, bronchoalveolar lavage fluid or tissue is the gold standard for diagnosis of coccidioidomycosis. Blood, cerebrospinal fluid and pleural or peritoneal fluids are less likely to be culture positive. Coccidioides may also be diagnosed by histopathologic examination although this is less sensitive than culture. On direct examination, visualization of the characteristic spherule containing endospores is diagnostic of infection (25). Spherules are not detected by Gram stain but microscopic identification may be aided by a variety of fungal stains such as calcofluor white, GMS and PAS. Coccidioides reverts back to the highly infectious mould form when cultured and care must be taken to prevent aerosolization and accidental inhalation in the laboratory. Thus it is imperative to notify laboratory personnel when Coccidioides is suspected. Serologic testing by various methods can be useful for diagnosing Coccidioides infection when histopathology or cultures are negative. However sensitivity of these assays may be lower in immunosuppressed patients and negative results do not exclude infection (36). Immunoglobulin M (IgM), also known as tube precipitin antibody, may be detected in serum within 1–3 weeks of acute Coccidioides infection. Immunoglobulin G (IgG), also known as complement-fixing antibody, develops after 2 weeks and may persist for several months. Complement-fixing IgG antibodies can be quantitated to assess the severity of infection; high or rising IgG antibody levels may be seen with worsening pulmonary infection or disseminated disease (25). Conversely, IgG antibody titers should decrease with effective therapy. Diagnosis and management of meningeal coccidioidomycosis requires lumbar puncture for CSF analysis. Since CSF cultures are often negative, complement-fixing IgG antibodies can be measured in cerebrospinal fluid and are diagnostic of meningitis (35). Other nonculture-based methods for diagnosis of coccidioidomycosis include enzyme immunoassay (EIA) and immunodiffusion. EIA uses antibodies to detect cell wall-derived fungal antigen excreted in urine, though it lacks specificity. The urine Histoplasma antigen EIA cross-reacts with Coccidioides antigen in approximately 58% of patients with coccidioidomycosis (37). A more specific urine Coccidioides antigen EIA has become available and may be useful for diagnosis of severe pneumonia or disseminated infections (37). In one study Coccidioides antigenuria was detected in two organ transplant recipients who had negative complement-fixing IgG antibody. These patients had disseminated coccidioidomycosis that was later confirmed by culture (37). Immunodiffusion is another method for measuring serologic response to infection and, although it has greater specificity for Coccidioides, may be less sensitive than EIA. The utility of these assays has not been studied extensively in organ transplant recipients. Immunosuppression leads to diminished immunoglobulin responses and false negative results have been observed in solid organ transplant recipients, complicating test interpretation and diagnosis (29, 31, 36). Treatment: Acute pulmonary coccidioidomycosis may be mild and self-limited in the immunocompetent host and antifungal therapy may be withheld with close clinical monitoring (III) (38). However all patients with underlying immune impairment, including organ transplant recipients, must be treated regardless of the severity of infection (III). As for blastomycosis, treatment of coccidioidomycosis in the setting of solid organ transplantation follows published guidelines (38). Treatment options for mild to moderate coccidioidomycosis include oral fluconazole or itraconazole (I) (38, 39). Amphotericin B, or preferably a less toxic lipid formulation, is generally reserved for severe pneumonia or disseminated infection (III). The decision to treat with oral versus intravenous therapy must be individualized, but symptom severity, respiratory status, extent of infection and the ability to take enteral therapy must be considered. Alternatively, meningeal coccidioidomycosis may be treated with high dose fluconazole (II-1), which has excellent CSF penetration, but lifelong therapy is necessary to prevent relapse (III). Repeat lumbar puncture during therapy to document improvement in CSF parameters and a decline in CSF complement-fixing antibodies is recommended (III). Favorable clinical responses have been demonstrated with voriconazole and posaconazole for treatment of refractory coccidioidomycosis or when toxicity develops to standard therapies (40, 41). The echinocandins have variable in vitro activity against Coccidioides and sufficient clinical data are limited at this time (20, 42, 43). Pretransplant evaluation: Preventing Coccidioides infection in solid organ transplant recipients is imperative since infection is frequently severe and mortality is high (30, 31). The risk of developing coccidioidomycosis following organ transplantation is greater in persons with a past history of infection or positive antibodies for Coccidioides prior to surgery (44). Clinicians must determine if transplant candidates have a history, even remote, of residence in or travel to an endemic area given the risk for reactivation of latent infection posttransplant. A history of prior infection should be elicited during the pretransplant evaluation and serologic testing performed. Antifungal therapy is recommended for transplant recipients with a past or recent history of coccidioidomycosis or positive Coccidioides serologies prior to surgery (III). Targeted antifungal prophylaxis, generally fluconazole, given to patients with a past history of Coccidioides infection or positive serologies has been successful in reducing recurrence of coccidioidomycosis following liver transplantation in endemic regions (II-1) (36). In addition, active infection or positive serologies in the donor necessitate antifungal prophylaxis for the organ recipient (30). When possible, organ transplantation should be deferred in patients with active coccidioidomycosis at the time of surgery until symptoms and signs of infection have resolved (III) (30). Lifelong antifungal prophylaxis is recommended for organ transplant recipients once active coccidioidomycosis has been controlled to prevent relapse. Chronic antifungal therapy is also recommended for transplant recipients if the donor had active Coccidioides infection or positive serologies (III) (44). Epidemiology and pathogenesis: Histoplasmosis is an opportunistic fungal infection caused by the dimorphic fungus, Histoplasma capsulatum. Although found in many areas of the world, the organism is endemic in the Ohio and the Mississippi River valley regions in the US. The clinical spectrum of infection is variable, ranging from a self-limited febrile illness to severe multiorgan dysfunction, depending on the size of the host inoculum and immune status of the infected individual. Posttransplantation histoplasmosis is rare, with an estimated incidence of <1%, even in endemic areas (2, 45). Human infection occurs via inhalation of H. capsulatum mycelia, typically found in high concentrations in excavated soil, avian or bat droppings in endemic areas. Exposure to disrupted soil around construction or agricultural areas, caves where bats reside or buildings inhabited by birds or bats pose particular risk. Once gaining access to the alveoli, the organism is engulfed by neutrophils and macrophages, then converted intracellularly from the mycelial to yeast form. Intracellular organisms can subsequently migrate to local lymph nodes and distant sites. Intact cellular immunity is critical to containing and eradicating Histoplasma infection, thus solid organ transplant recipients are at particular risk for significant infection. Histoplasmosis in transplant recipients can result from a primary infection via inhalation, reactivation of previous infection or rarely, transmitted via an infected allograft (46-48). Human to human transmission has not been reported. Clinical presentation: Though early case reports and series primarily described histoplasmosis among liver and kidney transplant recipients (49-51), more recent series also include heart, lung and kidney–pancreas transplant recipients (2, 45, 52). Based on these collective case reports and case series, histoplasmosis most commonly presents in an occult manner among transplant recipients, with the burden of disease often out of proportion to the severity of symptoms at the time of initial presentation. While an array of clinical manifestations have been reported in solid organ transplant recipients, the most common form is progressive disseminated infection, characterized as a subacute febrile illness with radiographic and/or laboratory evidence of extrapulmonary infection. The typical period from onset of symptoms to diagnosis is 2–4 weeks (2, 45, 52). As the infection progresses, frequent associated findings include hepatosplenomegaly, pneumonia, gastrointestinal involvement, pancytopenia, weight loss, hepatic enzyme elevations, mucosal/skin findings and increased lactate dehydrogenase levels. A thrombotic microangiopathy has also been reported as part of the clinical picture in more severely ill patients (53, 54). Most infections occur within the first 1–2 years after transplantation, though can present over a broad time range from months to several years posttransplant (2, 45, 52). Reports of histoplasmosis in transplanted children are few. However, in nonimmunosuppressed children, symptoms of histoplasmosis are similar to those that occur in adults, though meningitis accompanying progressive disseminated infection is more commonly seen in infants <2 years (55). Diagnosis: Confirmation of the diagnosis rests on direct visualization of H. capsulatum yeast forms with or without granulomas in involved tissues, culture growth of H. capsulatum and/or persistent antigenuria/antigenemia. The availability of newer generation antigen assays has improved early detection through increased sensitivity and specificity, as blood and tissue cultures may take up to 4 weeks to demonstrate growth (56, 57). The sensitivity of antigen detection is greater in urine than serum. The currently available third generation quantitative enzyme immunoassay for the detection of Histoplasma antigen demonstrates 100% sensitivity for antigenuria and 92.3% for antigenemia in AIDS patients with disseminated infection (56). Though not specifically studied in organ transplant recipients, recent case series suggest the sensitivity is comparable for patients with disseminated disease (2, 45, 52). The specificity of the third generation Histoplasma antigen assay is 99%, though limited in the setting of other endemic fungal infections due to a high degree of cross-reactivity with other fungal antigens (14, 56). Antigen testing is similarly useful in children. Histopathologic examination of biopsy specimens from suspected sites of involvement, including liver, lung, skin, lymph nodes and bone marrow can also expedite diagnosis. Special stains such as hematoxylin and eosin and Wright-Giemsa may aid in visualization of Histoplasma in blood or bone marrow while GMS or PAS may enhance visualization in tissue. While serologic testing is beneficial for the diagnosis of histoplasmosis in the normal host, the diagnostic utility of serologic testing is variable in organ transplant recipients (57, 58). For both immunosuppressed and nonimmunosuppressed individuals from endemic areas, potential background seropositivity confounds test interpretation. In healthy individuals with acute histoplasmosis, Histoplasma serology by immunodiffusion and complement fixation become positive in the majority of patients by 6 weeks. Seroconversion or 4-fold increase in titers strongly suggests the diagnosis of histoplasmosis. However, the effects of immunosuppressive agents on the humeral immune response may blunt the serologic response to infection, decreasing the sensitivity of the test in this setting (59). In a recent case series of organ transplant recipients with histoplasmosis, one third tested seropositive (45). Treatment: As the most common manifestation of histoplasmosis in solid organ transplant recipients is progressive disseminated infection, treatment recommendations will be limited to this form. For more detailed treatment recommendations for other forms of histoplasmosis, the reader is referred to the published 2007 IDSA clinical practice guidelines (60). Antifungal agents with proven efficacy in the treatment of progressive disseminated histoplasmosis include amphotericin B deoxycholate, liposomal amphotericin B (61), amphotericin B lipid complex (61) and itraconazole (62). Echinocandins have no established efficacy (20, 63). Mild to moderate infection may be treated effectively with itraconazole monotherapy (200 mg twice daily for at least 12 months), (II-2). For moderately severe and severe infection, initial therapy with amphotericin is recommended (I) (60). As there are no randomized studies of comparative efficacy in organ transplant recipients, the choice of amphotericin formulation is usually dictated by availability, cost and potential for nephrotoxicity. Amphotericin therapy should be continued for 1–2 weeks or until there is stabilization of the infection, followed by ‘step-down’ therapy with itraconazole (200 mg twice daily) to complete a 12 month total treatment course (60, 62). Concomitant reduction of immunosuppression is also an important treatment adjuvant if possible. Criteria for characterizing mild, moderate and severe illness is not well defined in the literature, but rather rest on clinical impression based on factors such as need for hospitalization, hemodynamic stability, respiratory status, extent of infection and ability to take oral medication. Treatment recommendations for children with progressive disseminated histoplasmosis are similar to adults, though longer initial courses of amphotericin are recommended based on published treatment experience (60). Amphotericin-associated nephrotoxicity is generally less severe in infants and children than adults (64). Other azole agents, specifically voriconazole (65), posaconazole (66, 67), fluconazole (68) and ketoconazole, all demonstrate in vitro susceptibility and limited clinical efficacy against H. capsulatum infections in small series and case reports. The data are inadequate to make treatment recommendations, thus these agents are considered second line treatment options for those individuals intolerant of itraconazole (III) (60). Urine and serum antigen levels typically fall with effective therapy and can be used to follow treatment response and assess for relapse. Antigen levels should be measured before treatment is initiated, at 2 weeks and 1 month, then every 3 months during therapy (II-2). Monitoring should continue at least 6 months after therapy is discontinued (57). Persistent low-level antigenuria is frequently observed in infected organ transplant recipients despite complete clinical response and an appropriate duration of therapy. Limited experience suggests that antifungal therapy can be safely withdrawn in this situation with careful monitoring for relapse (2, 60). Despite the severity of illness upon presentation, treatment efficacy among infected solid organ transplant recipients in the post-azole era ranges from 80 to 100% (2, 45, 52). Pretransplant evaluation: Pretransplant serologic and/or radiologic screening for prior histoplasmosis infection in endemic areas is not recommended based on the low likelihood of subsequent infection (69). Patients who have recovered from active histoplasmosis infection, with or without treatment, during the 2 years prior to the initiation of immunosuppression may be considered for itraconazole prophylaxis (200 mg daily), although the efficacy and appropriate duration of prophylaxis is unknown. Serial monitoring of urinary antigen levels in individuals with previous infection should also be performed during periods of intensive immunosuppression to monitor for relapse (III) (60). Management of individuals with incidental H. capsulatum detection in the explanted organ or donor tissue is not well established. This scenario occurs primarily in lung transplant recipients, and based on one center's experience, antifungal prophylaxis could be considered (45). Specific issues related to azole therapy: Drug–drug interactions are an important consideration when prescribing azole antifungal agents to organ transplant recipients. Azoles inhibit hepatic cytochrome P450 enzymes and modify the pharmacokinetics of the many drugs metabolized by this route. Azoles increase serum concentrations of cyclosporine, tacrolimus and sirolimus (70-72), thus drug levels of these immunosuppressive agents must be closely monitored in individuals during the initiation and discontinuation of azole therapy to prevent inadvertent drug toxicity or allograft rejection. Preemptive dose adjustment is recommended (I). Other immunosuppressive drugs such as mycophenolate, antithymocyte globulin, prednisone and alemtuzumab have no known drug–drug interactions with azoles (70). Pharmacokinetics of azole agents differ between adults and children in that children have more rapid drug clearance, necessitating more frequent and higher dose administration (64). Because of the potential hepatotoxic effects of azole use, hepatic enzymes should be monitored in all individuals before therapy is started, at 1, 2 and 4 weeks, followed by every 3 months during therapy (60). Issues related to itraconazole therapy deserve special consideration given the variable absorption among patients and among available drug formulations. The lipophilic composition of itraconazole limits its solubility and consequent gastrointestinal absorption. The bioavailability of oral itraconazole is dependent on the dosage formulation and the presence or absence of food. Food enhances the dissolution and absorption of itraconazole capsules, thus the dose should be taken with a full meal. As absorption is reduced with decreased gastric acidity, itraconazole capsules should not be co-administered with medications that lower gastric pH, such as antacids, H2 blockers or proton pump inhibitors (73-75). Conversely, capsule absorption can be enhanced when taken with an acidic beverage such as Coca-Cola (76). Itraconazole suspension is preferred over the capsule formulation owing to enhanced gastric absorption (77). Blood concentrations are ∼30% higher using the suspension rather than the capsule formulation (77). Itraconazole suspension does not require food or gastric acidity for absorption and is best taken on an empty stomach. Because of the marked intra- and interpatient variability in the pharmacokinetics and absorption of itraconazole, therapeutic monitoring of serum drug levels is strongly recommended to optimize therapy once steady-state has been reached (∼2 weeks) (III) (16, 78). Random itraconazole serum concentrations of at least 1.0 ug/mL (by HPLC) are recommended and correlate with clinical efficacy. Proia L.A.: Speakers' Bureau, Schering Plough. Miller R.: The author has nothing to disclose.