Increasing Incidence of mucormycosis in Spanish inpatients from 1997 to 2018

Mucormycosis is a worldwide angio‐invasive fungal infection that is associated with high morbidity and mortality. A few European studies have focused on the epidemiology.

gastrointestinal tract. 2 In immunocompromised individuals, infection usually begins in the nasal turbinates or the alveoli, and the resultant mortality, even with pharmacological and/or surgical treatment, is high unless the immune system status can be restored. Risk factors include diabetes mellitus, particularly with ketoacidosis, malnutrition, malignancies (lymphomas and leukaemias), organ transplant, trauma, burns and immunosuppressive therapy. [3][4][5][6][7][8] Patients on dialysis who receive treatment with the iron chelator deferoxamine are also more susceptible to mucormycosis. 9 Mucormycosis is less common in patients with AIDS because T cell-mediated immunity is not considered an important factor for triggering the infection. 10 The real incidence of mucormycosis is difficult to estimate since it is not a reportable disease and the risk varies widely in different populations and geographic regions. 11 A change in the incidence of mucormycosis is expected to be associated with an improved lifespan in cancer and transplant patients, as well as expanding indications for immunosuppressive medications for various autoimmune diseases.
The aim of this study was to estimate the incidence of mucormycosis in Spain and to describe the epidemiological and clinical characteristics of patients hospitalised in the National Health System (SNS) between 1997 and 2018.

| Data collection
Data were obtained from the Specialized Health Care Registry (RAE-CMBD in Spanish), which includes data on hospitalisation, outpatient surgery, day hospitalisation, and home and emergency hospitalisation. RAE-CMBD is the main Health Information System used to obtain statistical data and basic health indicators on morbidity and the care process of patients treated in Spanish hospitals. It contains information on general data (age, sex and place of residence), morbidity data and procedures performed (principal diagnosis or secondary diagnosis), variables related to the episode of hospitalisation, circumstance of admission (urgent or planned), patient discharge (discharge to home address, transfer to another hospital or death), stay and average cost.

| Data analysis
The incidence rate was calculated by dividing the number of new cases of zygomycosis/mucormycosis (numerator) per year/period by the population at risk (denominator) over a period of time (personyears) multiplied by 1,000,000 and expressed as 'cases per million person-years'. As it is not possible to accurately measure disease-free periods, the total figure of person-time at risk can be estimated approximately and satisfactorily when the size of the population is stable, multiplying the average population size studied by the duration of the observation period. Thus, the population at risk was obtained from annual data published by the National Institute of Statistics The 95% confidence interval (95% CI) for the incidence rate was calculated for a better clinical application of the results. Incidence rates were computed by autonomous community and year to assess temporal and geographical patterns. The results in terms of mean rates by autonomous community were plotted in maps for the whole study period. The lethality rate was calculated by dividing the number of principal diagnosis deaths (numerator) by the number of sick patients with a principal diagnosis of a specific disease (denominator) (x100). Pearson's correlation coefficient (rP) was calculated to assess the correlation between linear variables, incidence rate and environmental parameters. The weather parameters were obtained from the State Agency of Meteorology (AEMET, in Spanish, http://www. aemet.es/). The results are expressed as absolute values (n), proportions (n/N) and percentages (%) for categorical variables and as the mean, standard deviation (SD), median, interquartile range (IQR) (Q 3 -Q 1 ) and range (minimum value, maximum value) for continuous variables. The strength of the association between categorical variables was measured using Pearson's chi-square contrast statistic and the odds ratio (OR) estimate. Continuous variables were compared with Student's t test or the Mann-Whitney test for two groups, depending on their normal or non-normal distribution. ANOVA (F test) was used to statistically assess the equality of means between groups. The level of statistical significance was p < .05. Data analysis was performed using SPSS 26 (Statistical Package for the Social Sciences).

| Ethics statement
This study is based on medical data of patients collected in the CMBD. These data are the responsibility of the Ministry of Social Services of Health and Equality (Ministerio de Servicios Sociales, Sanidad e Igualdad, MSSSI) that maintain custody and organise them. All patient data provided by the CMBD are anonymised and deidentified by the MSSSI before they are provided to the applicants. According to this confidentiality commitment signed with the MSSSI, researchers cannot provide the data to other researchers, so other researchers must request the data directly from the MSSSI.
The protocol and ethics statement of this study were approved by the Clinical Research Ethics Committee of the Complejo Asistencial Universitario de Salamanca (CAUSA). Because the data were obtained from an epidemiological database, written consent was not obtained. All data were analysed anonymised. (p < .001).

| RE SULTS
A higher number of cases (277; 28.8%) occurred in the summer months: August (96; 10%) and September (101; 10.5%) were the months with the highest incidence of cases (see Figure 2). No seasonal variability was observed over the 22-year study period (p = .100). We assessed whether environmental parameters, such as temperature and precipitation, could condition variations between Spanish regions and over the study period (1997-2007 vs. 2008-2018). There was no statistically significant linear association between temperature, rainfall or autonomous community incidence rate (rP = 0.021; p = .933 and rP = 0.156; p = .524 respectively) or temperature, rainfall and time period incidence rate (rP = 0.324; P = .142 and rP = −0.143; p = .525 respectively) (see Figure 3).  F I G U R E 3 Pearson´s correlation coefficients between annual incidence rate (IR, cases per million person-years), annual rainfall (R, mm) and temperature (T, ºC) by time periods (1997-2007 vs, 2008-2018)

| DISCUSS ION
Mucormycosis is the third most common invasive fungal infection, following aspergillosis and candidiasis, 12 and it has a significant degree of morbidity and mortality. During the study period, 962 patients admitted for mucormycosis were registered, with a period incidence rate of 0.98 cases per million person-years. These data show that mucormycosis is an extremely rare infection in Spain, with incidences up to thirty times lower than those observed for Aspergillus, as previously shown. 13 However, the true incidence of mucormycosis may be higher, as many cases remain undiagnosed due to the difficulty in collecting samples from deep tissues and the low sensitivity of diagnostic tests. Nevertheless, during the study period, we detected a significant increase in the number of cases; in the second decade of the study, we found that the incidence of mucormycosis in Spain increased by 67% compared to the first part of the study. These data show an increasing number of cases in Spain that exceeds the estimates in other areas, such as Asia (31%) and North or South America (28%), Africa (3%), Australia and New Zealand (3%). 14 The rise is also very high in India and China among patients with uncontrolled diabetes mellitus. 15 In Europe, a few studies have focused on the incidence of mucormycosis, but it is not feasible to obtain exact incidence rates. 16 In a large national multicentre 10-   Type of discharge although very different methods were used to analyse the epidemiology, multiple studies have reported an increase in the incidence of mucormycosis as a result of the expansion of the population at risk and the use of prophylactic voriconazole, 19 as well as the optimisation of microbiology techniques for mucor isolation. 3 It is remarkable that the epidemiology of mucormycosis can vary with geographic region. 11 In our study, we investigated whether differences in climate could explain differences in the number of cases between different areas of our country, as suggested was the case for aspergillosis in a previous paper. 13 Although we detected a higher number of cases in the month of August, we did not find that rainfall, temperature or other factors were involved in differences associated with seasonality or differences in the incidence of this disease between different areas. Our data disagree with data shown by Rahal et al. 20 in which more than 60% of cases of mucormycosis occurred between May and August. The use of air conditioners and shared closed environments were postulated as possible explanations for this phenomenon. 20 In our study, the number of cases in men (69.1%) was double that of women (30.9%), which is in line with the results described in other works. 14,16,21 Another key epidemiological feature observed in our study was that the subjects were the same age as those in other works. Previous data showed that the median age of patients with mucormycosis varied from 50 to 54 years, which was similar to the mean age of 55 observed in our cohort. 14,19,21 We highlight in our work that more than 1/3 of the patients are over 65 years of age and only 3% are paediatric (<14 years). The main underlying diseases and and (iv) trauma, including secondary to an accident, major surgery and burns. Among patients with malignancies, haematologic malignancies are much more frequently associated with mucormycosis than solid tumours. 7 We emphasise that there are several differences in the prevalence of risk factors associated with mucormycosis between different areas worldwide. For example, in Europe and the United States, haematological malignancy (HM) 15 is the main factor involved (from 38% to 62% of the cases), whereas diabetes mellitus is the main factor in countries of Latin America like Mexico and Asian countries like Iran and India. 14,21-25 These data were similar to our results, with either diabetes or HM involved in more than onethird of all patients diagnosed with mucormycosis. In our work, we studied changes in the main factors associated with mucormycosis during the study period. We did not detect differences in the fre-  reported a mortality of 55%. 3 The differences in these data could be due to differences in treatment strategies. Unfortunately, due to the methodology of our study, we do not know the treatment selected or the location of mucormycosis, which could explain these differences. 28 Finally, it has recently been shown that the SARS-CoV2 infection is a new risk factor for mucormycosis, especially in countries with a high incidence such as India. 30 Thus, mucormycosis can occur among COVID-19 patients, especially with poor glycaemic control, widespread and injudicious use of corticosteroids and broadspectrum antibiotics, and invasive ventilation. 31 Unfortunately, it has not been possible to evaluate the impact of COVID on mucormycosis because of lack of available data in the Spanish health system during COVID-19 pandemic.
We also assessed the economic cost of mucormycosis in our country after not finding any literature about it. Health expenditure varies according to the different economic conditions of each country and the healthcare systems. Our data show that the total cost of mucormycosis per person is significant. The mean cost in Spain was higher than the total cost of the most prevalent inpatient pathology (eg pneumonia, heart failure and ischaemic stroke) and similar to the cost of sepsis (http://www.msssi.gob.es/). It should be noted that the estimated cost is only the cost due to hospitalisation, and other costs are not accounted for, so the final sum would be higher.

| Strengths and limitations
The CMBD is a database that continually collects information on hospital admissions for most of our hospitals, so the representative-  We have demonstrated that mucormycosis is a rare infectious disease in Spain, but it has had a significantly increased incidence in the last two decades. Being an adult male and having diabetes,

CO N FLI C T O F I NTE R E S T
The authors declare they have no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data available on request from the authors.