Surveillance study of the prevalence, species distribution, antifungal susceptibility, risk factors and mortality of invasive candidiasis in a tertiary teaching hospital in Southwest China

Invasive candidiasis (IC) is the most common fungal disease among hospitalized patients worldwide. According to conservative estimates, IC affects more than 250,000 people worldwide every year and is the cause of more than 50,000 deaths [1]. IC is widely reported in critically ill patients in the intensive care unit (ICU) [2]. The risk factors for IC included granulocytopenia, stem cell transplant, organ transplants, broad-spectrum antimicrobial agents, central venous catheterization, total parenteral nutrition, length of stay in the ICU, surgery, advanced life support, and aggressive chemotherapy [2]. With the increase of in related research, there have been reports showing that older age (over 65 years) [3], diabetes mellitus and chronic renal failure [4] are identified as risk factors for patients with IC

IC is caused by Candida species and comprises both candidemia and deep-seated tissue candidiasis. Candidemia is the most frequent form of IC. More than 15 Candida species can cause human candidemia [1, 2]. Deep-seated candidiasis is caused by either hematogenous dissemination or the direct inoculation of Candida species to a sterile site, such as the peritoneal cavity. Globally, Candida albicans is the primary cause of candidemia and one of the most common species in many countries, including Japan (39.5%) [5], Italy (61.2%) [6], Russia (43.2%) [7], Saudi Arabia (38.3%) [8] and Mexico (40%) [9], among others. However, Candida parapsilosis (17.8%) is the most common cause of IC in Pakistan [10]. The global incidence of IC varies from 0.3 to 5 per 1000 admissions according to hospital-based studies [11]. The mortality rate of IC in immunocompromised and other critically ill patients is between 35 and 80% [12]. The cost of IC treatment reached US$ 17,000 per patient in China, which was significantly higher than that for patients without IC (US$ 8500; P = 0.001) [13].

In China, the epidemiology of IC varies widely among different areas [14]. C. albicans (44.9%) is the most common strain isolated from IC patients in China, particularly in metropolitan cities [15]. Non-C. albicans species (59.9%) also play an important role in IC [16]. Data regarding epidemiologic trends and patient susceptibility to invasive fungal infections has mainly been studied in metropolitan cities, and little information from medium and small cities is known. Therefore, in the present study, we performed a five-year retrospective study to evaluate the epidemiology, antifungal susceptibility, risk factors and mortality of IC in patients in a tertiary teaching hospital in Southwest China.

A total of 243 distinct IC episodes were identified during our study period. The mean annual incidence of IC was 0.41/1000 admissions. A total of 209,611 cultures were also collected in our hospital; the positive rate of the fungal cultures was 4.3% (8963), 2.7% (243) of which corresponded to IC episodes from 21 wards. The culture-positive specimen came from the blood (116, 47.7%), sterile body fluid (98, 40.3%), central venous catheter tips (17, 7.0%) and sterile tissues (12, 4.9%). We classified all the wards into ICUs (42,17.3%), medical wards (103,40.3%) and surgical wards (98,42.4%). C. albicans was the predominant species in the ICU and surgical wards (50.0 and 51.5%, respectively), whereas C. glabrata was the predominant species (41.8%) in the medical wards (Fig. 1).

The cohort characteristics are described in Table 1; among the included patients (median age, 60 years), 57.2% were males. The percentages of the three most common isolated Candida species were as follows: C. albicans (45.3%), C. glabrata (30.0%) and C. tropicalis (15.2%) (Table 1). In patients in the age range of 49–65 years, C. glabrata was the predominant species (41.6%), but in patients in the age ranges of 16–49 and > 65, C. albicans was the main species (45.7 and 60.7%, respectively). The causative organism varied according to the age of the patients and their underlying diseases. With increasing age, the percentage of C. glabrata was reduced from 41.6 to 16.9%, and C. albicans and C. tropicalis significantly increased from 28.6 to 60.7% and from 11.4 to 15.7%, respectively. Non-C. albicans species were isolated with the highest frequency from patients with HIV/AIDS (84.6%); C. glabrata was the predominant species (76.9%). The incidence of IC increased from 0.16 episodes/1000 admissions in 2013 to 0.66 episodes in 2017, and the change in incidence over time was statistically significant (P < 0.05). A significant increase in the incidence (episodes/1000 admissions) of C. albicans (from 0.05 to 0.25), C. glabrata (from 0.06 to 0.23), C. tropicalis (from 0.03 to 0.12) and C. parapsilosis (from 0 to 0.03) was observed. The demographic and clinical characteristics of the patients are summarized in Table 1. Most of the patients had one or more comorbidities. The most common underlying comorbidities documented prior to IC were diabetes mellitus (38.3%), chronic/acute renal failure (37.0%), pulmonary infection (33.3%), cardiovascular disease (32.1%) and gastrointestinal pathology (25.9%). Moreover, the most common underlying conditions documented prior to IC were prior exposure to broad-spectrum antibiotics (88.5%), total parenteral nutrition (49.0%), central venous catheterization (48.6%), treatment with antifungal agents (37.6%) and mechanical ventilation (33.7%).

The results of in vitro susceptibility testing of the Candida strain isolates are summarized in Table 2. Among the Candida strains, AMB demonstrated excellent in vitro activity against all Candida species. All Candida strains (100%) were susceptible to AMB, while 95.9% of the isolates were susceptible to 5-FC. The resistance rate of ITR was the highest in the Candida species (23.1%). A total of 18.6% of the isolates were resistant to FCA. VRC resistance was observed in 18.5% of all the Candida isolates evaluated. The resistance rate of C. tropicalis was the highest among the Candida species; most of the isolates were resistant to FCA (29.7%), ITR (40.5%) and VRC (27.0%). The percentages of yeast isolates with resistance and decreased susceptibility to FCA, ITR and VRC were significantly decreased during the 5 years of observation. (Fig. 2).

The outcome data at day 30 were available for 243 episodes. The hospital mortality rate was 12.3%. The mortality rates among C. albicans, C. glabrata, C. tropicalis and Candida haemulonii infections were 18.2% (20 out of 110 patients), 8.2% (6 out of 73 patients), 8.1% (3 out of 37 patients) and 50.0% (1 out of 2 patients), respectively. Sixteen patients died within 7 days of obtaining a positive culture. Respiratory dysfunction (39.2%), intensive care in adults (28.5%), neutropenia (28.6%), severe autoimmune diseases (27.3%) and cardiovascular diseases (25.6%) were frequently associated with mortality during the study period.

The univariate predictors of poor outcomes due to IC are shown in Table 3. For patients with IC, the variables associated with 30-day mortality were as follows: respiratory dysfunction, pulmonary infection, cardiovascular disease, chronic/acute renal failure, mechanical ventilation, abdominal surgery, intensive care in adults, septic shock and IC due to C. albicans. The results of the multivariate analysis are listed in Table 4. Respiratory dysfunction [odds ratio (OR), 9.80; 95% confidence interval (CI), 3.24–29.63; P < 0.001] and IC due to C. albicans (OR, 3.35; 95% CI, 1.13–9.92; P = 0.029) were the independent predictors of 30-day mortality.

This was a single-center retrospective study in a regional tertiary teaching hospital in southwest China. The inpatients mainly came from Luzhou, Neijiang, Yibin, Zigong, Chishui, and Zhaotong cities, which are prefecture-level medium and small cities (urban resident population < 1000,000 persons) in western China [22]. The medium and small cities were defined in accordance with the new standard for city-size classification in China (http://​www.​gov.​cn/​zhengce/​content/​2014-11/​20/​content_​9225.​htm). The urban population proportion, gross domestic product, income of residents, educational resources, sports resources, medical resources and air pollution in medium and small cities are less than those in large cities [23‐25]; all the data are illustrated in the Additional file 1: Table S1.

Our data showed that the incidence of invasive Candida infection has increased steadily from 0.16 to 0.66 cases per 1000 admissions, which is similar to a metropolitan-based report in Beijing (0.13 to 0.55 cases per 1000 admissions), over the past 5 years [3]. However, the annual incidence of IC in our study (0.41 cases per 1000 admissions) was lower than those in metropolitan cities in China, such as Shanghai [26] (9.49 cases per 1000 admissions), and Nanjing [27] (0.71 to 0.85 cases per 1000 admissions). The reason for these different incidences might be that the subjects in Shanghai were mainly patients in ICUs wards, whereas the subjects in Nanjing were mainly patients with candidemia only.

In the study, C. albicans was the predominant species (50%) in the ICU. These results are consistent with a report from a multicenter prospective observational study in China [12]. However, in medical wards, the proportion of C. glabrata was higher than that of C. albicans, which was only exhibited in patients with hematological malignancies in the USA [28]. Although non-C. albicans species were significantly predominant, C. albicans was the most common isolate, consistent with reports from most other areas in China [26, 29‐31]. However, in Nanjing [27], C. tropicalis was the most common isolate (28.6%). A possible reason may be related to the type of infection (only candidemia). In our study, we also found that C. glabrata was the second most common Candida species, similar to a report from a hospital in China [30], and hospitals in Denmark [32], Germany [33] and the USA [34]. Besides, we found that invasive Candida infections occurred more frequently in males of advanced age (age > 65), which was similar with those findings in USA [35], Denmark [32], Pakistan [10], China (Beijing) [30] and China (Nanjing) [27], however, the actual reasons for this finding are not fully understood. In those patients aged 50 to 65 years old, C. glabrata was the most common Candida species; this result was different from a 133 sample-based study in China [27].

With regard to resistance, resistance to FCA, ITR and VRC were common in C. albicans and non-C. albicans species. Our studies showed that the ITR resistance rate was the highest, at 23.1% in all Candida species, followed by FCA (18.6%), VRC (18.5%) and 5-FC (4.1%). However, none of the isolates in this study were resistant to AMB, and the susceptibility results in our city were higher than those in northern Ireland (susceptibility, 99.1%) [36]. In China, the resistance rates vary significantly among different cities. As shown in Table 5, the total resistance rates of all Candida species in the study were higher than those in metropolitan cities, especially Beijing [37] and Chongqing [38], which were higher than those in the China Survey of Candidiasis (China-SCAN) study [12]. Possible reasons may be related to the irrational use of antifungal agents, in healthcare and veterinary settings and by the general public [39]. In contrast, the resistance rates in our study were lower than those in Nanjing [27]. Regarding other countries, the antifungal resistance rate in our study was higher than that reported in northern Ireland in 2007–2011 [36]. The resistance rate of azoles in C. albicans (< 5%) [40] worldwide was significantly lower than that in our study (> 20.0%). The results of the ARTEMIS DISK Global Antifungal Surveillance Study showed that FCA- and VRC-resistant isolates of C. glabrata (15.7 and 10.0% resistance, respectively) [29] were approximately 1.5 times more prevalent than those in our study (11.0 and 6.8% resistance rates, respectively). The resistance rate of ITR in our study (23.1%) was higher than that in the USA (21.1%) [34]. The proportion of VRC-resistant isolates in our study was similar to that observed in India (18.5% vs 18.7%) [41]. In addition, our data showed that the resistance rates of FCA, ITR and VRC were higher in 2013 than in 2014, but the resistance rate of isolates significantly increased in 2015. The percentages of yeast isolates with resistance and decreased susceptibility to FCA, ITR and VRC showed a significant decrease from 2015 to 2017 (Fig. 2). Moreover, the annual resistance rate of antifungal agents was associated with the usage frequency of antifungal agents (Fig. 2 and Table 6). Therefore, it is necessary to surveil the changes in the resistance rate of antifungal agents.

In this study, we analyzed the prognostic factors in patients with IC. Respiratory dysfunction, pulmonary infection, cardiovascular disease, chronic/acute renal failure, mechanical ventilation, abdominal surgery, intensive care in adults, septic shock and IC due to C. albicans were the predictors of mortality in the univariate analysis (P < 0.05). The number of prognostic factors (9 factors) in our city was clearly more than that in other regions of China, such as Beijing [3], Shanghai [26], Chongqing [38], Nanjing [27] and Jinan [4], and all the data are illustrated in the Additional file 2: Table S2. The differences in the prognostic factors in different cities might be related to the underlying diseases of patients in different cities, but the actual reasons are still unclear. Out of all the variables that were significantly associated with mortality in the univariate analysis, respiratory dysfunction and IC due to C. albicans were the predictive factors of mortality in the multivariate analysis. The results of some factors in this study agreed with the findings of a multicenter prospective observational study in China [31] and a retrospective analysis in Mexico [9]. In a study of critically ill patients, IC-associated mortality accounted for 58.6% [8]; the crude 30-day mortality rate in our study was only 12.3% in all patients with IC, which was substantially lower than the mortality rates reported in Italy (42.8%) [42], Mexico (38%) [9], Pakistan (52.1%) [10], Spain (30.0%) [43], Jinan (23.1%,China) [4] and Nanjing (26.0%,China) [27]. The reason for the high mortality rate might be that the research subjects in those countries and cities were mainly ICU-patients or patients with candidaemia. Those cases often had more severe underlying diseases and conditions, which are associated with high mortality, therefore having a higher risk of mortality [44, 45]. Conversely, the percentages of ICU patients and patient with candidemia in our study were only accounted for 17.3 and 47.7%, respectively. The lower mortality rate in our study was also identified in the Pu, S, et al. [38] with similar subjects in Chongqing. In our study, the mortality rate due to C. haemulonii was the highest (50%, 1/2), possibly because there were only two cases. The fatal case in our study was a critically ill patient in the ICU with respiratory dysfunction and severe underlying comorbidities. Excluding C. haemulonii, C. albicans was associated with the highest mortality rate (18.2%). In our study, respiratory dysfunction was the major cause of mortality (39.2%) in patients (OR, 9.80; 95% CI, 3.24–29.63; P < 0.001); Meanwhile, another study also indicated that hematological malignancy was also an independent predictor for 66.7% of death of in-hospital patients [27]. Certainly, the severity of the underlying comorbidities (hematological malignancy and respiratory dysfunction) considerably influenced the crude mortality rate in this patient population.

This study has several potential limitations. First, the subjects in our study were restricted to adult patients (> 16 years old). Therefore, our conclusions may not be extrapolated to pediatric patients. Second, due to the technical limitations of the clinical microbiology laboratory and the impact of hospital policies, there are no data on echinocandins in our hospital. Finally, this was a single-center retrospective study. Our data might be influenced by the distribution of the regional population, the level of medical intervention, and the distribution of patient types.

This study shows that the incidence and mortality of IC in medium and small cities are lower than those in large cities, that the resistance rate to azoles is higher in medium and small cities than in large cities, and that the species distribution and risk factors in medium and small cities are different from those in large cities in China. This study provides reference data for future epidemiological and susceptibility studies on both antifungal agents and mortality due to IC in our hospital and in other hospitals in medium and small cities.