The Clinical Epidemiology of Pulmonary Cryptococcosis in Non-AIDS Patients at a Tertiary Care Medical Center

Introduction Cryptococcus neoformans is a ubiquitous saprophytic fungus with worldwide distribution. It has been found in nature, primarily in association with bird droppings, but nonavian sources have been described as well (10). Although the lungs are thought to be the portal of entry for cryptococcus, pulmonary infection is uncommon. The organism is trophic to the central nervous system and the vast majority of recognized infections involve meningitis. Before the acquired immunodeficiency syndrome (AIDS) epidemic (1980), cryptococcosis was a rare infection, and pulmonary disease was described in 10%–45% of patients with cryptococcal meningitis (2). However, the true incidence of pulmonary cryptococcosis (PC) was not known, but was much lower than meningitis. Most PC cases were identified histologically and often at autopsy, with only about 20% diagnosed by culture (2,3,13). In recent years, many of the reports of cryptococcal infection have been in the human immunodeficiency virus (HIV)-positive population, and little is known of the disease in non-AIDS patients, particularly pulmonary involvement. At our institution, a tertiary care medical center with a large transplant program, sporadic cases of PC have occurred in solid-organ transplant recipients as well as in patients with a variety of different medical conditions. The purpose of our study was to investigate the epidemiology of PC in non-AIDS patients, and to determine predictors of outcome among these patients. Patients and Methods Patients All patients with PC who received care at the University of Pittsburgh Medical Center, Pittsburgh, PA, between January 1991 and June 1999 were identified from 145 microbiology and pathology records. Chart review All medical records of the study patients were reviewed from the hospital’s electronic information database MARS (Medical Archival Retrieval System). Included in this database are the admission history and physical examination results, discharge summary, dictated progress notes, medications dispensed from the pharmacy, and all laboratory data including microbiology and pathology reports. The admission history and physical examination were reviewed for the presence and duration of fever, cough, and shortness of breath; patients were assessed for the presence of respiratory failure requiring mechanical ventilation and meningitis. Demographic data, dates of admission and discharge, dates of organ transplant operations, diagnostic procedures, and the outcome of present hospitalization were collected and tabulated. Recorded microbiology data included the date, specimen site, and results of cultures of all specimens and results of cryptococcus antigen in serum and cerebrospinal fluid (CSF). Pathology data obtained included the date, specimen type (bronchoalveolar lavage or lung biopsy), and results of grocott and mucicarmine stains. The primary cause of death was obtained from the discharge summary or autopsy report. Chest radiology Chest radiographs and computed tomography studies were reviewed by 2 thoracic radiologists for the presence and type of pulmonary infiltrates and the presence of nodules, cavitations, mass densities, and pleural effusions. Definitions The date of diagnosis of PC was defined as the date of the obtained specimen that yielded positive culture or positive biopsy. PC was defined as identification of Cryptococcus neoformans from bronchoalveolar lavage by culture, lung cytology, or lung biopsy and abnormal chest radiography. Patients with sputum culture positive for Cryptococcus neoformans without clinical and radiologic manifestations of pneumonia were excluded from the study. Disseminated cryptococcosis was defined as PC together with evidence of cryptococcus outside the respiratory tract. Cryptococcus-related mortality was defined as death that was directly attributed to cryptococcosis (that is, cryptococcus was recovered at autopsy). In cases in which an autopsy was not performed, patients whose deaths occurred during the first 4 weeks of treatment of cryptococcosis were considered to have cryptococcosis-related mortality (5). Acute respiratory failure was defined as hypoxemia (PO 2 <60 mmHg) requiring mechanical ventilation. Severity of illness was evaluated by acute respiratory failure requiring mechanical ventilation and the use of positive end-expiratory pressure (PEEP) during ventilatory support. Microbiology Before April 1, 1995, all respiratory tract specimens submitted to the microbiology laboratory for fungal culture were inoculated onto Sabouraud dextrose agar and mycophil agar containing antibiotics (penicillin and gentamicin). Since then the inoculation of all pulmonary specimens for fungal culture was done on inhibitory mold agar slants (IMA, Becton Dickinson, Cockeysville, MD) and brain heart infusion agar slants with 10% sheep blood containing antibiotics (BHI wAb; chloramphenicol and gentamicin, Becton Dickinson, Cockeysville, MD). Cultures were incubated at 30 °C and were examined daily during the first week and then weekly for the following 3 weeks. Cryptococcal serum antigen was prepared with the use of Cryptococcal antigen latex agglutination system (Meridian Diagnostics, Cincinnati, OH) and performed according to the manufacturer’s protocol. Statistical analysis Continuous data are presented as the mean ± standard deviation (SD) or median and range, and categorical data as proportions. The standard 2-sample t-test was used to test differences between means, while differences in proportions were tested using the Fisher exact test. The Wilcoxon rank sum test, a nonparametric equivalent to the standard 2-sample t-test, was used for highly skewed data. A p value less than 0.05 was considered statistically significant. All tests were 2-tailed. A univariable analysis was performed to investigate potential prognostic factors for cryptococcus-related mortality using the Fisher exact test or the Wilcoxon rank sum test, where appropriate. Prognostic factors studied included age at time of diagnosis, number of days to the diagnosis of PC, culture specimen, development of acute respiratory failure requiring mechanical ventilation, presence of meningitis, administration of amphotericin B alone or amphotericin B with 5-flucytosine, pulmonary infiltrates, pulmonary nodules, unilateral versus bilateral lung disease, and presence of pleural effusions. A stepwise multivariable modeling procedure using backward elimination method was performed to select risk factors associated with cryptococcus-related mortality. Any variable whose univariable test result had a p value < 0.050 was considered a candidate for the multivariate model. Once the variables were identified, the model-building process began with a model containing all the selected variables. The statistical criteria for inclusion and exclusion at each step of the model building process was a p value < 0.15 and a p value > 0.20, respectively. The multivariable modeling procedure was performed using the Cox proportional hazards regression analysis. Results Between January 1991 and June 1999, 38 cases of PC in non-AIDS patients were diagnosed at the University of Pittsburgh Medical Center. All patients were hospitalized. These included 25 (66%) solid-organ transplant (SOT) recipients and 13 (34%) nontransplant (non-SOT) patients. The incidence of PC by year during the study period is shown in Figure 1.Fig. 1: The annual incidence of pulmonary cryptococcosis over a 9-year period (1991–1999) per 10,000 hospital admissions was calculated by dividing the number of cases each year by the number of total admissions at the midpoint of each year. This assumes that admissions followed a uniform distribution.Demographics Of the 25 SOT recipients, 18 (72%) were male and 7 (28%) female. The mean age at the time of diagnosis for SOT recipients was 55 ± 10 years (range, 31–71 yr), and 96% (n = 24) were caucasian. The type of transplant organ is presented in Table 1. All patients received immunosuppressive therapy, which included tacrolimus (n = 19) or cyclosporine A (n = 6) with or without prednisone. The median time interval between transplantation and the diagnosis of PC was 11 months (range, 0.5–130.3 mo). Seven patients (28%) were diagnosed within 6 months of transplantation and an equal number were diagnosed at least 2 years after transplantation. Of the 13 non-SOT patients, 10 (77%) were male and 3 (23%) were female. The underlying medical conditions at the time of diagnosis of PC in the non-SOT group are presented in Table 2. Of the 13 patients, 5 were receiving immunosuppressive therapy as part of the treatment for their underlying disease. This included prednisone in 3 patients and tacrolimus in 2 patients.TABLE 1: Overall incidence of pulmonary cryptococcosis (PC) by type of solid-organ transplant recipientTABLE 2: Underlying medical conditions in the nontransplant patient population with pulmonary cryptococcosis (PC)Clinical presentation and manifestations Presenting symptoms at the time of diagnosis of PC were reported in a total of 28 (74%) patients. Of these, the most common symptoms were shortness of breath (50%) followed by cough (46%) and fever (43%). A comparison of presenting symptoms between SOT and non-SOT patients is presented in Table 3. None of the symptoms reported was significantly different between the 2 patient groups (p > 0.05). The length of symptoms in days was significantly shorter in SOT recipients (mean, 12.1 ± 3 d) compared with non-SOT patients (mean, 18.9 ± 3 d) (p = 0.029). Five of 11 patients who had lumbar puncture at the time of diagnosis of PC were found to have cryptococcal meningitis. All cases occurred in SOT recipients. The chest radiology findings in all PC cases included infiltrates (51%), pulmonary nodules (47%), and pleural effusions (18%). No statistically significant difference was observed in the percentage of patients with unilateral and bilateral lung involvement between the patient groups (see Table 3).TABLE 3: Comparison between solid-organ transplant recipients and nontransplant patients with pulmonary cryptococcosisMicrobiologic characteristics Cryptococcus neoformans was recovered from bronchoalveolar lavage in 21 (55%) patients, lung biopsy/histology in 25 (66%), and pleural fluid 2 (5%) patients. Extrapulmonary cultures were positive in 5 patients. Of the 38 cases, serum cryptococcal antigen test was performed in 28 (74%); 15 were positive and 13 negative. All 5 patients with extrapulmonary cryptococcosis had a positive serum cryptococcal antigen. Other cultures obtained at the time of PC diagnosis did not yield any additional pathogen. Severity of illness Acute respiratory failure requiring mechanical ventilation developed in 8 patients. The median time between PC diagnosis and initiation of mechanical ventilation was 2 days (range, 1–5 d). Ventilatory support ranged from 1 to 9 days. PEEP was added to the management of all the patients. There was no statistically significant difference in the frequency of acute respiratory failure between SOT and non-SOT patients (see Table 3). Treatment Most of the SOT recipients were treated with a combination of amphotericin B and 5-flucytosine (52%); 3 were treated with amphotericin B alone and 7 with fluconazole. In the non-SOT group, treatment consisted of amphotericin B alone (n = 6), combination of amphotericin B and 5-flucytosine (n = 1), fluconazole (n = 1), and itraconazole (n = 1). Mortality In the SOT group, 5 patients (20%) died. Of the 5 deaths, 4 were related to cryptococcus. In the non-SOT group, 4 patients (31%) died; all which were related to cryptococcus. Autopsy was performed in 3 patients (2 SOT, 1 non-SOT) and findings included bilateral multilobar lung involvement (n = 3), mediastinal lymph nodes (n = 2), meningitis (n = 2), and kidney involvement (n = 1). By univariable analysis only 2 factors were associated (that is, p < 0.05) with cryptococcus-related mortality: acute respiratory failure requiring mechanical ventilation (50% versus 13%, p = 0.044) and pleural effusion (57% versus 13%, p = 0.025). Using Cox proportional hazards regression the only factor independently associated with cryptococcus-related mortality was pleural effusion (hazard rate ratio = 5.4; 95% confidence intervals: 1.3–21.9). The association of pleural effusion and acute respiratory failure was examined using the Fisher exact test. Patients with pleural effusion were more likely to have acute respiratory failure compared with patients without pleural effusion (3/7, 43% versus 5/31, 16%; p = 0.146). Patients with pleural effusion also had a higher mean serum creatinine at the time of diagnosis compared with patients without pleural effusion (3.6 ± 1.8 versus 1.7 ± 1.0, respectively; p = 0.01 Wilcoxon rank sum test). Discussion Previous reports have described that the prevalence of cryptococcosis is markedly increased among patients with defects in the cell-mediated arm of the immune system such as occurs in patients with AIDS, lymphoma, chronic leukemias, collagen vascular disease, sarcoidosis, and those receiving immunosuppressive drugs (2,3,10). In a recent population-based surveillance of cryptococcosis, 14% of the cases (135 patients) occurred in non-AIDS patients, but only 29% (44 patients) had pulmonary disease. Overall, cancer and diabetes mellitus were the most commonly reported conditions in the HIV-negative population. However, most of the patients in the study with diabetes also had 1 or more immunocompromising conditions (7). In our cohort of non-AIDS patients with PC, most of the cases occurred in persons with known risk factors for cryptococcosis. These included SOT recipients, cancer patients, individuals receiving immunosuppressive therapy (autoimmune diseases), and patients with idiopathic CD4 lymphopenia. This is a change in the epidemiology of this infection since before the HIV epidemic, when 30%–50% of cases were described in apparently healthy individuals (2,3). Organ transplantation was the most frequent underlying condition in our study. This finding is consistent with other recent reports, which described that organ transplantation has remained as 1 of the major risk factors for cryptococcosis in HIV-negative patients. Indeed, it has been estimated that 10%-20% of the cases of cryptococcosis in non-AIDS patients come from this patient population (1,3,11). Studies before and after the HIV epidemic have reported a predominance of male patients among individuals with cryptococcosis (2–4,7,9). This was also the case in our study of PC where the majority of patients were male. Some authors have suggested a difference in male and female host immune systems as a possible explanation for the male predominance among patients with cryptococcosis (3). The majority of our patients with Cryptococcus lung involvement were symptomatic at the time of diagnosis (74%), and 8 (21%) of the patients with PC developed acute respiratory failure. This clinical presentation is in contrast to the subclinical pneumonitis often reported of patients with PC (1–3,9). Kerkering et al (9) reviewed PC before the HIV epidemic and described 34 of 41 (81%) patients with underlying immunocompromised condition. The most common presenting symptoms were fever, malaise, chest pain, weight loss, and dyspnea, but despite the fact that 28 patients had disseminated disease, none developed acute respiratory failure. While the etiology of respiratory failure associated with cryptococcal disease in our patients is multifactorial, the extent of cryptococcal infection in the lungs and involvement of other organs might have played an important role in the pathogenesis of acute respiratory failure in these patients. Indeed, animal models of PC have indicated that in addition to the well-appreciated role of host immune status, difference in the organism’s ability to induce the pulmonary inflammatory response may determine the course of clinical infections (4). Our findings confirm that nonspecific symptoms are the predominant manifestation of PC and no significant differences are observed between transplant and nontransplant recipients (2,9). The cryptococcal serum antigen was positive in only 15 patients with PC, 5 of whom had a concomitant extrapulmonary site of cryptococcal infection, a finding suggestive that screening with serum cryptococcal antigen with a latex agglutination test may not facilitate the diagnosis of PC without extrapulmonary cryptococcal infection. In fact, reports in HIV-positive and -negative patients (8,14) have suggested the unreliability of the serum latex agglutination test for the diagnosis of PC, which may be negative even in the presence of extensive pulmonary disease. Hence, a high index of suspicion for PC should remain in the differential diagnosis of patients at risk for cryptococcosis. Risk factors for poor outcome despite treatment for cryptococcosis in non-AIDS patients have been described mainly among patients with meningitis. These include lymphoreticular malignancy, glucocorticoid therapy, CSF with high opening pressure, low glucose, less than 20 leukocytes/mm 3 , a positive India ink smear, cryptococci isolated from extraneural site, and high titers of cryptococcal antigen in the CSF or serum (2,5). In our analysis the only factor independently associated with cryptococcosis-related mortality was pleural effusion. Pleural effusions have been described during cryptococcosis. Reports have indicated that they may be present with or without evidence of pulmonary infection and can occur in both immunocompetent and immunosuppressed hosts (6,9,12,13,15). We also found that patients with pleural effusion were more likely to have acute respiratory failure. These factors may be indicative of extensive cryptococcal disease. Indeed, autopsy finding in 3 of the 8 patients with cryptococcus-related mortality showed extensive bilateral multilobar lung disease. Patients with pleural effusion also had respiratory failure and higher serum creatinine compared with patients without pleural effusion. Perhaps the most likely explanation for this finding is that patients with pleural effusions had extensive cryptococcosis. Thus, in the multivariate analysis, the only significant prognostic marker of poor outcome among patients with PC was pleural effusion. In conclusion, our study suggests that cases of symptomatic PC occur in patients with impaired immunity. This may represent a major change in the epidemiology of PC since before 1980, when the majority of cases were described in apparently healthy individuals. Perhaps this is the reflection of the increasing number of patients receiving chronic immunosuppressant agents. Moreover, PC in immunocompromised non-AIDS patients presents usually as symptomatic disease and may have a more rapid clinical course than previously reported. The presence of pleural effusion in these patients is a prognostic factor of poor outcome. Summary Although the lungs are thought to be the portal of entry for Cryptococcus neoformans, pulmonary infection is relatively rare. We examined the clinical presentation, manifestations, and predictors of outcome of pulmonary cryptococcosis (PC) in non-AIDS (acquired immunodeficiency syndrome) patients. Between January 1991 and June 1999, 38 cases of PC were identified for study enrollment: 25 (66%) were solid-organ transplant (SOT) recipients and 13 (34%) were nontransplant (non-SOT) patients. Seventy-two percent of the study patients were symptomatic at the time of diagnosis. Factors associated with cryptococcus-related mortality in SOT and non-SOT patients were acute respiratory failure requiring mechanical ventilation (50% versus 13%, p = 0.04), pleural effusion (57% versus 13%, p = 0.022), and bilateral parenchymal lung disease (35% versus 9%, p = 0.059). A multivariate regression analysis found pleural effusion to be the only factor associated with cryptococcus-related mortality (hazard rate ratio = 5.4; 95% confidence intervals: 1.3–21.9). PC in immunocompromised non-AIDS patients usually presents as symptomatic disease and may have a more rapid clinical course than previously reported. The presence of pleural effusion in these patients is a prognostic marker of poor outcome.