Epidemiology and Outcomes of Extrapulmonary Invasive Fungal Infections After Kidney Transplantation in Northern India

ABSTRACT

Background

Extrapulmonary invasive fungal infections (IFIs) in kidney transplant recipients (KTRs) are understudied, particularly in endemic, resource‐limited settings. This study evaluated the epidemiology, risk factors, and outcomes of extrapulmonary IFIs in KTRs in northern India.

Methods

In this nested case‐control study of 1649 KTRs (2007–2022), microbiologically proven extrapulmonary IFI cases were identified from microbiology and histopathology databases.

Results

Extrapulmonary IFI occurred in 67 KTRs (4.1%). Cryptococcosis (46.3%) and candidiasis (20.9%) were the predominant infections. The central nervous system was the most common site (44.8%), followed by the bloodstream (22.4%). The mean age was 46.78 years, and 85.1% were males. The median time to infection was 55 months posttransplant, and 79.1% of infections occurred beyond 1 year posttransplant. Median estimated glomerular filtration rate (eGFR) was 43 mL/min/1.73 m², and acute graft dysfunction was present in 49.3% cases. Comorbidities included diabetes (44.8%), chronic renal allograft injury (59.7%), acute rejection (38.8%), bacterial infection (26.9%), and cytomegalovirus disease (13.4%). Diabetes (OR 2.27, p = 0.038) and methylprednisolone pulses for rejection (OR 3.19, p = 0.025) were independently associated with IFI. Infection‐related mortality was 35.8%; disseminated infection (HR 3.72, p = 0.020) and requirement for kidney replacement therapy (KRT) (HR 3.98, p = 0.011) independently predicted death. Note that, 5‐ and 10‐year patient survival was significantly lower in cases than in controls (74.1% and 48.3% vs. 92.3% and 74.9%; p = 0.008), whereas death‐censored graft survival was comparable.

Conclusions

Extrapulmonary IFIs are late‐onset and commonly present as cryptococcal meningitis or candidemia. Diabetes and methylprednisolone pulses increase infection risk, while dissemination and KRT requirement predict mortality.

Among 67 kidney transplant recipients with extrapulmonary invasive fungal infections from India, cryptococcal meningitis and candidemia were most common and occurred late post‐transplant. Diabetes and steroid pulses increased infection risk, while the dissemination and dialysis need predicted 35.8% mortality. Long‐term survival was worse than controls despite preserved grafts.

Abbreviations

ADPKD

autosomal dominant polycystic kidney disease

ATG

antithymocyte globulin

CAKUT

congenital anomalies of kidney and urinary tract

CMV

cytomegalovirus

CNI

calcineurin inhibitor

CNS

central nervous system

COVID‐19

coronavirus disease

CRAI

chronic renal allograft injury

eGFR

estimated glomerular filtration rate

EORTC/MSGERC

European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium

HR

hazard ratio

IFI

invasive fungal infection

IQR

interquartile range

IVIg

intravenous immunoglobulin

KOH

potassium hydroxide

KRT

kidney replacement therapy

KTR

kidney transplant recipient

OR

odds ratio

PCR

polymerase chain reaction

SARS‐CoV‐2

severe acute respiratory syndrome coronavirus 2

SD

standard deviation

1. Introduction

Kidney transplantation improves survival and quality of life in patients with end‐stage kidney disease (ESKD) compared with dialysis [1]. Despite the recent advances in immunological and therapeutic fields, infections remain a significant challenge. About 80% of patients experience an infectious episode within the first posttransplant year [2, 3]. Invasive fungal infections (IFIs) account for only 5%–10% of infections in kidney transplant recipients (KTRs) but are associated with significant morbidity and mortality [4, 5, 6]. The burden is particularly high in developing countries, like India, where factors such as hot and humid climate, overcrowding, malnutrition, poverty, and poor healthcare facilities increase susceptibility to infection [7, 8].

Although the classic posttransplant infection timeline described by Rubin and coworkers stratifies the risk of infection after transplantation, IFI can occur at any time, from the immediate postoperative period to several years later, depending on the net state of immunosuppression and environmental exposures [6, 9, 10]. The lungs are the common site of involvement, as fungal spores are primarily acquired through inhalation [11, 12, 13]. Pulmonary infections typically present with overt symptoms, such as cough, dyspnea, and fever, prompting patients to seek medical attention in the early stages of disease [14]. In contrast, extrapulmonary infections result from direct inoculation or hematogenous dissemination from a primary site, often the lungs [15, 16]. These infections may follow a slow, indolent course and present with nonspecific or subtle symptoms, such as fever of unknown origin or altered sensorium, often leading to delayed diagnosis and poorer outcomes.

While pulmonary IFIs are well‐documented in the literature, a critical knowledge gap exists regarding extrapulmonary IFIs after kidney transplantation, particularly in high‐risk, resource‐limited settings. The large multicenter studies, such as the TRANSNET registry, have focused on Western populations and pulmonary presentations, leaving the spectrum and determinants of extrapulmonary disease underexplored in endemic regions [17]. To address these uncertainties, this nested case‐control study aimed to study the epidemiology, risk factors, and outcomes of extrapulmonary IFIs in KTRs at our institution.

2. Material and Methods

2.1. Study Design and Patients

This nested case‐control study was conducted within a cohort of 1649 KTRs who underwent transplantation between January 2007 and December 2022 at a major transplant center in Northern India. Cases included KTRs who developed extrapulmonary IFIs during the posttransplant period. For each case, one KTR without fungal infection who underwent transplantation immediately before or after the case was selected as a control. Patients with isolated pulmonary infections, superficial mucocutaneous infections (including localized phaeohyphomycosis), or asymptomatic fungal colonization without tissue invasion were excluded.

2.2. Data Collection

Cases were identified by systematically screening electronic medical records, including microbiology and histopathology databases. The data collected included demographic information, the occurrence and treatment of acute rejection episodes in the year preceding infection, tissue‐invasive cytomegalovirus (CMV) disease diagnosed after transplantation and before IFI, concomitant bacterial infections, and other comorbidities such as diabetes, chronic renal allograft injury (CRAI), and chronic viral hepatitis. Invasive diagnostic procedures, including nasal endoscopy, lumbar puncture, and tissue biopsy (including postmortem biopsy), were performed to confirm the diagnosis. The site of infection, culture findings, fungal pathogen, and patient status at last follow‐up were recorded.

2.3. Definitions

Extrapulmonary IFI was defined as a microbiologically proven infection involving sites beyond the lungs, such as the central nervous system (CNS), bloodstream, or allograft. Diagnosis required at least one of the following: (1) histopathological evidence of fungal elements in a biopsy specimen, (2) positive culture from a tissue specimen, or (3) direct microscopic evidence on potassium hydroxide (KOH) mount of tissue specimens or aspirates from involved lesions. For suspected cryptococcal meningitis, an India ink preparation of cerebrospinal fluid was also performed. Cryptococcal antigen testing was not routinely performed throughout the study period and was therefore not included in the diagnostic criteria. The European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium (EORTC/MSGERC) criteria for possible, probable, and proven IFI were not applied separately; however, all included cases corresponded to proven IFIs [18].

The site of infection was determined by a positive specimen obtained directly from the site or by radiographic evidence of involvement of the site with a positive specimen from another site. Disseminated infection was defined as involvement of at least two noncontiguous anatomical sites or the bloodstream by the same fungal pathogen. Dual infection refers to infection with two different fungal pathogens, occurring either simultaneously or at different times. Infection‐related mortality was defined as death directly or indirectly attributed to infection, based on clinical, microbiological, and imaging evidence, irrespective of the severity or prognosis of concurrent comorbid conditions. Graft failure was defined as loss of kidney allograft function requiring chronic dialysis and/or retransplantation. Relapse is the recurrence of infection by the same fungal pathogen after an initial response to therapy.

2.4. Institutional Protocol

• Induction: Patients receive either antithymocyte globulin (ATG) or basiliximab or no induction according to immunological risk stratification.

• Maintenance Immunosuppression: The standard triple‐drug regimen includes prednisolone, calcineurin inhibitor (CNI: tacrolimus or cyclosporine), and antimetabolite (mycophenolate mofetil or azathioprine). The regimen is modified during an infectious episode; the antimetabolite is usually reduced or stopped first. If the infection is nonresponsive or progressive, the CNI is also tapered or withdrawn [19]. In patients receiving azole antifungals, the CNI dose is reduced due to potential drug interaction, and CNI trough levels are closely monitored [20].

• Acute Rejections: The cellular rejections were treated with three to five doses of 500 mg intravenous methylprednisolone initially, followed by oral prednisolone to reach nadir in the next 4 weeks. Steroid‐resistant cases were treated with ATG, while antibody‐mediated rejections were usually treated with plasmapheresis and intravenous immunoglobulin (IVIg).

• Antimicrobial Prophylaxis: Cotrimoxazole prophylaxis is used for 1 year and restarted for 6 months if the patient receives augmented immunosuppression for rejection [21]. Oral clotrimazole solution is used to prevent oropharyngeal candidiasis for the initial year [22]. Broad‐spectrum mold prophylaxis is not routinely used at our center. Valganciclovir prophylaxis for CMV is given for 6 months in high‑risk donor‐seropositive/recipient‐seronegative (D+/R−) transplants, ATG induction, ABO‐incompatible transplantation, or HLA desensitization [23].

• Antifungal Therapy: Mucormycosis, cryptococcosis, and histoplasmosis were treated with induction therapy using amphotericin B for 3–4 weeks, followed by step‐down maintenance therapy with posaconazole, fluconazole, and itraconazole, respectively [19, 24, 25]. Liposomal amphotericin B was preferred because of its improved safety profile; however, deoxycholate formulations were used in cases of financial constraints. Invasive aspergillosis was managed with voriconazole as first‐line therapy [26]. Candidemia was generally treated with echinocandins, whereas disseminated mold infections were managed with amphotericin B induction followed by pathogen‐specific azole maintenance therapy [27].

2.5. Ethical Approval

The study was approved by the Institutional Ethics Committee of Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, with reference number: 2023‐156‐DM‐132, and was conducted in accordance with the principles of the Declaration of Helsinki. Informed consent was waived due to the retrospective nature of the study.

2.6. Statistical Analysis

All statistical analyses were performed using IBM SPSS software, version 29.0. Continuous variables were expressed as means ± standard deviations or medians (interquartile ranges [IQRs]) and compared using Student's t‐test for normally distributed data or Mann–Whitney U test for non‐normally distributed data. Categorical variables were expressed as frequencies and percentages and compared using chi‐square or Fisher's exact tests. Univariable and multivariable logistic regression models were used to identify risk factors associated with extrapulmonary IFI. Infection‐related mortality was assessed using the Cox proportional hazards regression model, with time origin defined as the date of IFI diagnosis and censoring at last follow‐up or non‐infection‐related death. Kaplan–Meier curves were used to compare overall patient and death‐censored graft survival between cases and controls from the time of transplantation, using the log‐rank test. All statistical tests were performed at a 5% level of significance, and p values < 0.05 were considered statistically significant.

3. Results

3.1. Clinical Spectrum of Extrapulmonary IFIs

Extrapulmonary IFI was identified in 67 (4.1%) of 1649 KTRs. The mean age at diagnosis was 46.78 ± 11.61 years, and most cases were male (85.1%, n = 57). The median time from transplantation to infection was 55 months (IQR: 17–97), with the majority of infections occurring beyond 12 months posttransplant (79.1%, n = 53). At diagnosis, the median estimated glomerular filtration rate (eGFR) was 43 mL/min/1.73 m² (IQR: 31–64), and acute graft dysfunction was present in 49.3% (n = 33) cases.

The identified infections were cryptococcosis (46.3%, n = 31), candidiasis (20.9%, n = 14), mucormycosis (14.9%, n = 10), aspergillosis (10.4%, n = 7), histoplasmosis (4.5%, n = 3), and phaeohyphomycosis (3.0%, n = 2). The CNS was the most frequently involved site (n = 30, 44.8%), followed by bloodstream infection or fungemia (n = 15, 22.4%). Graft kidney involvement occurred in three cases: one each of mucormycosis, aspergillosis, and candidiasis. Three cases had concomitant pulmonary lesions with the same fungal pathogen, two mucormycosis and one aspergillosis, and were classified as disseminated infections. Overall, dissemination was observed in 24 (35.8%) cases.

Direct microscopy or histopathology was positive in all cases, whereas fungal culture yielded growth in 42 (62.7%) cases. Dual infections with two distinct fungal pathogens occurred in four (6.0%) cases: two cases of cryptococcal meningitis with pulmonary aspergillosis, one case of cryptococcal meningitis with candidemia, and one case of candidemia with pulmonary mucormycosis. The etiological and anatomical distributions are summarized in Table 1.

TABLE 1.

Etiological spectrum and anatomical distribution of extrapulmonary invasive fungal infections in kidney transplant recipients (n = 67).

Causative organism	n (%)
Cryptococcosis	31 (46.3%)
CNS (meningitis)	29
Bloodstream	2
Candidiasis	14 (20.9%)
Bloodstream	12
Graft kidney	1
Ear	1
Mucormycosis	10 (14.9%)
Sinonasal	4
Liver abscess	3
Graft kidney	1
Thyroid tissue	1
Bloodstream	1
Aspergillosis	7 (10.4%)
Sinonasal	5
Graft kidney	1
Eye	1
Histoplasmosis	3 (4.5%)
Oral ulcer	2
Lymph node	1
Phaeohyphomycosis	2 (3.0%)
CNS (brain abscess)	1
Sinonasal	1

Abbreviation: CNS, central nervous system.

3.2. Risk Factors for Extrapulmonary IFIs

Baseline characteristics of cases and controls are summarized in Table 2. The baseline characteristics were broadly comparable, although chronic hepatitis (17.9%, p = 0.014) and use of methylprednisolone pulses for rejection (35.8%, p = 0.005) were more frequent in cases. Diabetes mellitus, CRAI, acute rejection, and ATG use were also more common among cases but did not reach statistical significance.

TABLE 2.

Baseline characteristics of extrapulmonary invasive fungal infection cases and matched controls.

Characteristics	Case (n = 67)	Control (n = 67)	p value
Age at transplantation, years, mean ± SD	41.51 ± 11.35	42.47 ± 14.00	0.666
Sex, n (%)
Males	57 (85.1%)	55 (82.1%)	0.641
Females	10 (14.9%)	12 (17.9%)
Donor relation, n (%)
Living‐related	35 (52.2%)	29 (43.3%)	0.209
Living‐unrelated (spousal)	27 (40.3%)	36 (53.7%)
Living‐unrelated (non‐spousal)	5 (7.5%)	2 (3.0%)
Native kidney disease, n (%)
Unknown	52 (77.6%)	52 (77.6%)	0.790
Diabetic kidney disease	7 (10.4%)	4 (6.0%)
Chronic glomerulonephritis	3 (4.5%)	6 (9.0%)
CAKUT	2 (3.0%)	2 (3.0%)
ADPKD	1 (1.5%)	2 (3.0%)
Renal calculus disease	1 (1.5%)	1 (1.5%)
Chronic interstitial nephritis	1 (1.5%)	0
ABO‐incompatibility, n (%)	2 (3.0%)	5 (7.5%)	0.441
Re‐transplantation, n (%)	2 (3.0%)	1 (1.5%)	1.000
Induction, n (%)
Basiliximab	30 (44.8%)	27 (40.3%)	0.562
ATG	15 (22.4%)	13 (19.4%)
Daclizumab	1 (1.5%)	0
No induction	21 (31.3%)	27 (40.3%)
Calcineurin inhibitors, n (%)
Tacrolimus	53 (79.1%)	57 (85.1%)	0.328
Cyclosporine A	14 (20.9%)	9 (13.4%)
None	0	1 (1.5%)
Antimetabolite, n (%)
Mycophenolate mofetil	61 (91.0%)	65 (97.0%)	0.425
Azathioprine	4 (6.0%)	2 (3.0%)
Everolimus	1 (1.5%)	0
None	1 (1.5%)	0
Delayed graft function, n (%)	5 (7.5%)	6 (9.0%)	0.753
Baseline creatinine, mg/dL, mean ± SD	1.17 ± 0.31	1.17 ± 0.26	0.988
Biopsy‐proven acute rejections and management	26 (38.8%)	18 (26.9%)	0.141
ATG	11 (16.4%)	5 (7.5%)	0.110
Methylprednisolone pulse	24 (35.8%)	10 (14.9%)	0.005
Plasmapheresis with IVIg	7 (10.4%)	9 (13.4%)	0.594
Comorbidities, n (%)
Diabetes mellitus	30 (44.8%)	20 (29.8%)	0.074
Chronic renal allograft injury	40 (59.7%)	31 (46.3%)	0.119
Cytomegalovirus disease	9 (13.4%)	6 (9.0%)	0.411
Chronic hepatitis	12 (17.9%)	3 (4.5%)	0.014
Tuberculosis	17 (25.4%)	15 (22.4%)	0.685
COVID‐19	12 (17.9%)	9 (13.4%)	0.476
Concomitant bacterial infection	18 (26.9%)	—	—

Abbreviations: ADPKD, autosomal dominant polycystic kidney disease; ATG, anti‐thymocyte globulin; CAKUT, congenital anomalies of kidney and urinary tract; COVID‐19, coronavirus disease; IQR, interquartile range; IVIg, intravenous immunoglobulin; SD, standard deviation.

All cases received living‐donor kidneys: 35 (52.2%) related, and 32 (47.8%) unrelated, including 27 spousal donors. Two (3.0%) cases had undergone a second transplant, and two (3.0%) were ABO incompatible transplants, desensitized with rituximab and plasmapheresis. Induction therapy was used in 46 (68.7%) cases (basiliximab, n = 30; ATG, n = 15; daclizumab, n = 1), and all except one received triple immunosuppression with prednisolone, CNI, and an antimetabolite.

Comorbidities included diabetes mellitus in 30 (44.8%) cases, CRAI in 40 (59.7%), prior tissue‐invasive CMV disease in 9 (13.4%), and chronic hepatitis in 12 (17.9%; hepatitis B, n = 6; hepatitis C, n = 4; dual infection, n = 2). Acute rejections within the preceding year occurred in 26 (38.8%) cases, and all received augmented immunosuppression, including methylprednisolone pulses (n = 24), ATG (n = 11), plasmapheresis with IVIg (n = 7), rituximab (n = 1), and bortezomib (n = 2).

In addition, 18 (26.9%) cases had concomitant bacterial infections, and 17 (25.4%) had been treated for tuberculosis. COVID‐19‐associated infections were observed in 12 (17.9%) cases during recent or active SARS‐CoV‐2 infection, which included sinonasal mucormycosis (n = 4), sinonasal aspergillosis (n = 3), cryptococcal meningitis (n = 2), sinonasal phaeohyphomycosis (n = 1), and candidemia (n = 2).

On multivariable analysis, diabetes mellitus (adjusted odds ratio [OR]: 2.27, 95% CI: 1.05–4.94; p = 0.038) and methylprednisolone pulses for acute rejection (adjusted OR: 3.19, 95% CI: 1.15–8.82; p = 0.025) were independently associated with extrapulmonary IFI. Additional risk factors are presented in Table S1.

3.3. Treatment

All cases were managed with pathogen‐directed systemic antifungal therapy according to institutional protocol. Graft nephrectomy was required in two cases of aspergillosis and candidiasis involving the allograft, while graft mucormycosis was diagnosed only on postmortem biopsy. All cases of fungal sinusitis underwent endoscopic sinus surgery with debridement of the sinus cavity. Enucleation was performed in the only case of ocular aspergillosis. Supportive measures included kidney replacement therapy (KRT) in 15 (22.4%) cases and mechanical ventilation in 18 (26.9%) cases.

Simultaneously, the immunosuppressive drug regimen was modified as per the institute's protocol. The antimetabolite was temporarily discontinued, and the CNI dose was reduced by half. In patients receiving azoles, the CNI dose was further reduced, and trough levels were monitored closely. Despite the above measures, seven cases were readmitted with CNI toxicity and required additional dose reduction. However, there were no episodes of graft rejection following modification of immunosuppression.

3.4. Outcomes

Infection‐related mortality was observed in 24 (35.8%) cases. The causes of death included Cryptococcus meningitis (n = 9), mucormycosis (n = 5), candidemia (n = 5), aspergillosis (n = 3), and disseminated phaeohyphomycosis (n = 2). On multivariable Cox regression analysis, disseminated infection (adjusted hazard ratio [HR] = 3.72, 95% CI: 1.23–11.24; p = 0.020) and the requirement for KRT (adjusted HR = 3.98, 95% CI: 1.37–11.55; p = 0.011) were independently associated with increased mortality; other factors are summarized in Table S2.

Among the 33 (49.3%) cases with acute graft dysfunction, 14 had partial or complete recovery, whereas 19 did not recover or worsened, including 4 graft losses during the index episode. During a median follow‐up period of 17 months (IQR 4–38) among survivors, 6 relapsed requiring additional antifungal therapy, 7 died, and 6 had graft loss.

Overall patient survival at 5‐ and 10‐year posttransplant was 74.1% and 48.3% in cases, significantly lower than in controls (92.3% and 74.9%; p = 0.008) (Figure 1a). In contrast, the corresponding death‐censored graft survival rates were 93.2% and 77.6% in cases, comparable to controls (100% and 90.7%; p = 0.477) (Figure 1b).

FIGURE 1.

Kaplan–Meier survival curves comparing kidney transplant recipients with extrapulmonary invasive fungal infections and matched controls: (a) Overall patient survival and (b) death‐censored graft survival after transplantation.

3.5. Fungal Pathogen‐Specific Clinical Features and Outcomes

Table 3 shows heterogeneity in clinical presentations and outcomes across fungal pathogens. Cryptococcosis was less frequently disseminated (16.1%) but associated with considerable mortality (29%). In contrast, candidiasis, mucormycosis, and aspergillosis were more commonly disseminated, often complicated by acute graft dysfunction requiring KRT, and associated with high mortality (35%–50%). Histoplasmosis, although rare, occurred late after transplantation with relatively preserved graft function and no deaths. Notably, both cases of disseminated phaeohyphomycosis presented with graft dysfunction and resulted in fatal outcomes, highlighting the particularly poor prognosis of disseminated infection. Culture positivity also varied by pathogen, being higher in candidiasis (85.7%) and cryptococcosis (67.7%), and lower in aspergillosis (42.9%) and mucormycosis (40.0%).

TABLE 3.

Pathogen‐specific clinical features and outcomes of extrapulmonary invasive fungal infections.

	Cryptococcosis (n = 31)	Candidiasis (n = 14)	Mucormycosis (n = 10)	Aspergillosis (n = 7)	Histoplasmosis (n = 3)	Phaeohyphomycosis (n  = 2)
Age at diagnosis, years, mean ± SD	47.19 ± 13.00	45.29 ± 10.59	41.70 ± 8.19	47.71 ± 11.44	59.33 ± 3.79	54.00 ± 8.48
Males, n (%)	26 (83.9%)	10 (71.4%)	10 (100%)	6 (85.7%)	3 (100%)	2 (100%)
Donor relation, n (%)
Living‐related	18 (58.1%)	8 (57.1%)	5 (50.0%)	2 (28.6%)	0	0
Living‐unrelated	13 (41.9%)	6 (42.9%)	5 (50.0%)	5 (71.4%)	3 (100%)	2 (100%)
Induction, n (%)
Basiliximab	10 (32.3%)	7 (50.0%) a	6 (60.0%)	6 (85.7%)	2 (66.7%)	0
ATG	5 (16.1%)	5 (35.7%)	3 (30.0%)	1 (14.3%)	1 (33.3%)	0
No induction	16 (51.6%)	2 (14.3%)	1 (10.0%)	0	0	2 (100%)
Maintenance immunosuppression, n (%)
Tacrolimus	23 (74.2%)	12 (85.7%)	9 (90.0%)	5 (71.4%)	3 (100%)	1 (50.0%)
Cyclosporine A	8 (25.8%)	2 (14.3%)	1 (10.0%)	2 (28.6%)	0	1 (50.0%)
Mycophenolate mofetil	27 (87.1%)	13 (92.9%)	9 (90.0%)	7 (100%)	3 (100%)	2 (100%)
Azathioprine	3 (9.7%)	1 (7.1%)	0	0	0	0
Everolimus	1 (3.2%)	0	0	0	0	0
Comorbidities, n (%)
Diabetes mellitus	16 (51.6%)	5 (35.7%)	4 (40.0%)	3 (42.9%)	2 (66.7%)	0
Chronic renal allograft injury	20 (64.5%)	9 (64.3%)	6 (60.0%)	1 (14.3%)	0	2 (100%)
Biopsy‐proven acute rejections	15 (48.4%)	2 (14.3%)	5 (50.0%)	2 (28.6%)	0	2 (100%)
Cytomegalovirus disease	3 (9.7%)	2 (14.3%)	2 (20.0%)	2 (28.6%)	0	0
Chronic hepatitis	8 (25.8%)	3 (21.4%)	0	3 (42.9%)	0	0
Tuberculosis	7 (22.6%)	6 (42.9%)	1 (10.0%)	3 (42.9%)	0	0
COVID‐19	2 (6.5%)	2 (14.3%)	4 (40.0%)	3 (42.9%)	0	1 (50.0%)
Concomitant bacterial infection	2 (6.5%)	7 (50.0%)	1 (10.0%)	0	0	1 (50.0%)
Time from transplant to infection diagnosis, months, median (IQR)	55 (28–96)	57.5 (10.25–102.25)	6 (2–53.5)	76 (4–97)	76 (74–166)	110.5 b
Culture positivity	21 (67.7%)	12 (85.7%)	4 (40.0%)	3 (42.9%)	0	2 (100%)
Disseminated infection, n (%)	5 (16.1%)	11 (78.6%)	6 (60.0%)	4 (57.1%)	1 (33.3%)	2 (100%)
eGFR at diagnosis, mL/min, median (IQR)	43 (31–64)	37.5 (17.25–54.5)	38.5 (14.5–74.25)	48 (44–63)	67 (56–93)	40.5 b
Acute graft dysfunction, n (%)	11 (35.5%)	10 (71.4%)	5 (50.0%)	5 (71.4%)	0	2 (100%)
Kidney replacement therapy, n (%)	4 (12.9%)	4 (28.6%)	4 (40.0%)	2 (28.6%)	0	1 (50.0%)
Mechanical ventilation	6 (19.4%)	4 (28.6%)	4 (40.0%)	3 (42.9%)	0	1 (50.0%)
Infection‐related mortality, n (%)	9 (29.0%)	5 (35.72%)	5 (50%)	3 (42.9%)	0	2 (100%)
Relapse, n (%)	3 (9.7%)	0	1 (10.0%)	1 (14.3%)	1 (33.3%)	0

Abbreviations: ATG, antithymocyte globulin; COVID‐19, coronavirus disease; IQR, interquartile range; SD, standard deviation.

^a Includes one case of daclizumab. ^b IQR not estimable

4. Discussion

This study is one of the largest single‐center analyses of extrapulmonary fungal infections in KTRs. The CNS was the most frequently involved extrapulmonary site, followed by bloodstream infections. Accordingly, cryptococcosis was the predominant infection, followed by candidiasis, mucormycosis, and aspergillosis. Most infections occurred beyond the first posttransplant year, which may be due to limited use of ATG induction, Candida prophylaxis during the initial year, the cumulative effects of prolonged immunosuppression, associated comorbidities, and ongoing environmental exposures.

Fungal pathogens in organ transplant recipients show distinct site predilections. In the TRANSNET study (2001–2006), which documented 1208 IFIs across 23 US centers, candidiasis predominantly presented as bloodstream infection (64%), aspergillosis as pulmonary disease (78%), cryptococcosis involved CNS (45%) or lungs (39%), and endemic mycoses like histoplasmosis were usually disseminated. Mucormycosis (then termed zygomycosis) affected lungs (56%), sinuses (13%), skin (13%), or was disseminated (9%) [17]. In our cohort of extrapulmonary infections, Cryptococcus predominantly presented as meningitis, consistent with its neurotropism, which is mediated by cryptococcal virulence factors that enhance blood–brain barrier permeability [28, 29]. Candida species, commensal yeasts, likely breached mucosal or skin barriers in immunocompromised transplant recipients and predominantly caused bloodstream infections [30]. Aspergillus and mucormycetes affected diverse extrapulmonary sites, such as the paranasal sinuses, liver, and kidney allografts. Our findings highlight pathogen‐specific tissue tropism and the impact of regional ecological factors on the epidemiology of these infections.

The pathogenesis of IFI is influenced by the virulence of the pathogen, the host's immune status, and environmental factors [15]. The intensity and duration of immunosuppressive therapy directly correlate with the risk of infection [31]. ATG induction alone does not increase the risk of IFI; however, its antirejection utilization does increase the risk, particularly at higher cumulative doses [32, 33]. Similarly, intravenous methylprednisolone pulses given for acute rejection are recognized risk factors for IFI [34, 35]. The standard of care for antibody‐mediated rejection, plasmapheresis with IVIg, has variable effects; plasmapheresis impairs humoral immunity, while IVIg exerts a protective effect for infection [36]. In our cohort, the heightened net state of immunosuppression frequently extended beyond the early posttransplant period, likely due to augmented immunosuppression for acute rejection in 38.8% of patients; methylprednisolone pulses were associated with IFI development. Among other conventional risk factors, such as diabetes, CMV infection, prolonged antibiotic exposure, dialysis dependence, viral hepatitis, preexisting renal failure, and retransplantation, only diabetes showed an independent association with IFI [37, 38, 39, 40].

The management of IFIs requires a careful balance between pathogen‐directed therapy and adjustment of immunosuppression [10]. In this cohort, guideline‐based pathogen‐directed therapy was employed, with amphotericin B used for severe or disseminated disease and azoles or echinocandins utilized for step‐down or pathogen‐specific treatment [19, 24, 25, 26, 27]. Immunosuppression was systematically reduced by withholding antimetabolites and reducing CNI doses in life‐threatening infections [19]. Drug interactions, particularly CYP3A4 inhibition by azoles, remained a significant challenge [20]. We did not observe rejection episodes after the modification of immunosuppression, suggesting that dose reduction may be safely implemented under careful supervision. The role of antifungal prophylaxis is controversial, as it may promote drug resistance and has not demonstrated a mortality benefit in clinical trials [41, 42, 43]. Further, KTRs have a lower risk of developing IFIs compared to other solid organ transplant recipients [17]. However, it may be considered in high‐risk situations, such as antirejection therapy, fungal colonization, CMV infection, prior use of broad‐spectrum antibiotics, prolonged ICU stay, or persistent neutropenia [42].

Mortality from IFIs in KTRs varies by pathogen, with reported rates between 25% and 50% [5, 6]. We observed an overall mortality of 35.8%, consistent with previous studies. Dissemination was a major determinant of mortality, likely due to a higher organism burden, diagnostic delays, and multisystem involvement. The need for KRT was the other key predictor, reflecting the cumulative impact of severe sepsis, graft dysfunction, nephrotoxic antifungals, and CNI–azole interactions. Mechanical ventilation, required in 75% of deaths versus none of the survivors, further emphasizes the severity and irreversibility of multi‐organ failure. Long‐term patient survival was significantly lower in extrapulmonary IFI cases than in matched controls. The high mortality likely reflects the heightened net state of immunosuppression, predisposing these patients to severe and often fatal infections [10]. In contrast, graft survival was well preserved and comparable to that of the control group. Most patients died with a functioning allograft, indicating that infection‐related mortality, rather than graft failure, was the principal determinant of long‐term outcomes.

This study has important implications for kidney transplant practice, particularly in endemic, resource‐limited settings. The predominance of late‐onset CNS cryptococcosis and bloodstream candidiasis underscores the need for continued vigilance beyond the early posttransplant period. High‐dose methylprednisolone pulses were associated with extrapulmonary IFI, highlighting the importance of judicious augmentation of immunosuppression in high‐risk recipients. A low threshold for invasive biopsy can facilitate diagnosis by culture or histopathology in settings with limited access to advanced diagnostic facilities. Dissemination and the need for KRT, and respiratory failure are practical markers of infection‐related mortality, supporting early risk stratification, timely escalation to intensive care, and prognostic counseling. Immunosuppression could be cautiously reduced without precipitating rejection, with close monitoring of drug levels and graft function. Despite preserved graft survival, long‐term patient survival was markedly reduced, emphasizing the need for prevention, early recognition, and aggressive treatment of extrapulmonary IFI to sustain the survival benefit of kidney transplantation.

Several limitations should be acknowledged. The long study period was necessary because IFIs are uncommon in KTRs, but it introduced heterogeneity in patient characteristics and management practices over time. The retrospective, single‐center design limits generalizability and introduces selection bias. The restricted use of advanced diagnostic techniques (e.g., beta‐D‐glucan, polymerase chain reaction [PCR] assays) and reliance on conventional mycological methods in resource‐limited settings may have resulted in underdiagnosis. Despite the extended study duration, the number of cases remained small, limiting detailed characterization of less common pathogens, such as phaeohyphomycosis, and of endemic infections, such as histoplasmosis. In addition, the absence of antifungal susceptibility testing restricted the evaluation of resistance patterns and pathogen‐specific therapy. However, the study's large cohort, detailed analysis of site‐specific pathogens and mortality predictors provide valuable insights into these infections in resource‐limited settings.

5. Conclusion

Extrapulmonary invasive fungal infections occur predominantly late after transplantation, most commonly as cryptococcal meningitis or candidemia, and are associated with high infection‐related mortality. Diabetes mellitus and high‐dose methylprednisolone pulses increase the risk of extrapulmonary IFI, while dissemination and the need for KRT are strongly associated with death. Despite preserved graft function, long‐term patient survival is significantly lower than in controls, indicating that infection‐related mortality rather than graft failure determines adverse outcomes. These findings emphasize the need for sustained vigilance in high‐risk recipients, prompt diagnostic evaluation of suspected IFI, and careful adjustment of immunosuppression once diagnosis is confirmed.

Author Contributions

Abdullah: methodology, investigation, data curation, formal analysis, writing – original draft, writing – review and editing. Anupma Kaul: conceptualisation, methodology, supervision, writing – review and editing, validation. Rungmei Marak: data curation, supervision, visualisation. Manas Behera: methodology, investigation, data curation, writing – review and editing. Narayan Prasad: validation, supervision, writing – review and editing. Manas Patel: formal analysis, project administration. Dharmendra Bhaduaria: methodolgy, conceptualisation, writing – review and editing. Ravi Kushwaha: data curation, supervision, resources. Monika Yachha: visualization, writing – review and editing. Akash Mishra: formal analysis, software, validation.

Funding

The authors have nothing to report.

Supporting information

Supporting File 1: tid70218‐sup‐0001‐SupMat.docx.

Supporting File 2: tid70218‐sup‐0002‐VisualAbstract.jpg.