Introduction

In recent years, leptospirosis has gained increasing attention as an emerging infectious disease of global importance [1]. The clinical manifestations range from asymptomatic infection to severe and potentially fatal illness complicated by septic shock and organ failure [2]–[5]. The broad clinical spectrum is presumably one of the main reasons why diagnosis of this spirochaetal infection remains a challenge for clinicians. Over years, leptospirosis has been reported to occur rarely in Austria and Germany [6], [7]. Diagnostic testing for the infection is therefore performed only in specialized reference hospitals. The low leptospirosis incidence rate reported for Germany and Austria appears discordant, however, with the high rate of Leptospira spp. seropositivity among healthy Austrian men identified by Poeppl and colleagues [8].

Hawaii has the highest reported annual incidence rate of leptospirosis in the United States, reaching 1.63 cases per 100,000 inhabitants [9]. Lower annual incidence rates have been reported from Central and Western Europe ranging from 0.06/100,000 per year in Germany over 0.1/100,000 in the United Kingdom and 0.25/100,000 in the Netherlands to 0.5/100,000 in France [6], [7], [10]–[12]. An increasing proportion of the leptospirosis infections diagnosed in many European countries is imported from abroad (25% to 60% of all infections) [10], [12]–[14]. Most of the imported infections have been associated with sporting and adventurous vacation activities abroad [14]–[16].

The objectives of this study were to determine the epidemiology of leptospirosis in South-East Austria, to describe risk exposures for acquiring autochthonous infection, and to compare clinical characteristics of patients with imported to those with autochthonous infection.

Methods

Over a 9-year period (2004–2012), all patients with clinically compatible illness that have been tested positive by rapid point-of-care (POC) test for Leptospira-specific IgM (Leptocheck®, Zephyr Biomedicals, India) at the microbiology laboratory, University Hospital Graz, were included. The hospital has a capacity of more than 1500 beds and serves as reference hospital for about 1 million inhabitants in South-East Austria. If borderline positive test results were obtained with the routine microbiological evaluation, a repeat test was ordered within a few days to confirm the infection.

Microscopic agglutination testing (MAT) was performed on a subset of specimens at the Institute for Veterinary Disease Control in Moedling (AGES), for detection of the causative Leptospira serovar. A titre greater than 200 against any of the pathogenic antigens was considered positive. We defined all patients with positive POC test and clinically compatible illness as cases of leptospirosis, independent of MAT result, because the POC IgM test was recently shown to be more sensitive than MAT (85.6% versus 49.8%), with comparable specificity (96.2% versus 98.8%) in a study evaluating results in more than 1500 cases of leptospirosis [17]. In another recent study comparing prospectively three POC tests for Leptospira-specific IgM the Leptocheck® IgM POC test, which was also used in this study, showed the best results with an overall sensitivity of 78% and a specificity of 98% [18].

Data regarding course of disease as well as risk exposures (within three weeks before onset of infection) were collected via telephone questionnaires (n = 82; conducted between June 2012 and January 2013) and/or abstracted from electronic hospital databases (n = 127). Infections in patients that had travelled in foreign countries within three weeks before occurrence of symptoms were classified as potentially imported [17]. All other infections were classified as autochthonously acquired.

Questionnaire responses were entered into an electronic database. All statistical analyses were performed using the Statistical Package for Social Sciences version 20.0 (SPSS Inc., Chicago, IL, USA). Continuous data are presented as medians (inter-quartile ranges [IQR]) or means (95% confidence interval [CI]) and categorical data as proportions. Proportions were compared using the chi-squared or Fisher’s exact test as appropriate. Analyses of continuous data were performed using the Mann-Whitney U test or Students T-test as appropriate. Bootstrapping was used to calculate the 95% CI for proportion by gender.

The study was conducted according to the principles expressed in the Declaration of Helsinki and was approved by the local ethics committee, Medical University of Graz. All data presented have been de-identified and are therefore not attributable to individual patients. At our center, information of all patients admitted is automatically stored in the electronic hospital database, and written informed consent of participating patients was waived by the local ethics committee.

Results

A total of 127 adult patients (range 18–89 years) with positive Leptospira specific IgM tests were identified while the test resulted negative in another 794 patients. 114/127 (89.8%) patients had acquired leptospirosis within Austria and 13 (10.2%) had potentially imported infections (Table 1). No outbreak was observed during the study period. In 80/127 (63%) patients single serum samples were received for MAT testing, which turned out positive in 61 (76%) and negative (i.e. titre <200) in 19/80 patients (24%). Cases per year (autochthonous and imported) are shown in Table 1. Median duration of symptoms prior to presentation at the hospital was 5 days (IQR 3–9 days) and the median length of hospitalization was eight days (IQR 5–12 days); neither parameter differed between autochthonous and imported cases. Four autochthonous and two potentially imported cases had severe infections requiring ICU admission secondary to sepsis and organ failures; all six patients survived.

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Table 1. Demographic data as well as recreational/occupational and residential risk exposures in autochthonous cases (overall, males, females) and imported cases.

https://doi.org/10.1371/journal.pone.0085974.t001

Discussion

We found that leptospirosis is endemic in South-East Austria. Our findings would correspond to an autochthonously acquired infection rate of 1.26 per 100,000 inhabitants per year in South-East Austria over the study period. The estimated incidence probably reflects the more severe end of the clinical spectrum for leptospirosis, as mild forms of this disease are more likely to remain unrecognized and may have presented to smaller peripheral hospitals or family doctors, i.e. settings where testing for leptospirosis is yet not performed.

Therefore we believe that the actual rate of leptospirosis in South-East Austria may be much higher than the rate reported here. Although it is required by law to report basic demographic data of all serologically confirmed leptospirosis cases to the Austrian Government the official numbers may suffer from underreporting for two reasons: (i) the fact that leptospirosis cases are rarely confirmed by serological tests in Austria as diagnostic testing for the infection is performed in a few specialized reference hospitals only, (ii) the suboptimal reporting behaviour of clinicians. It is interesting that a recent cross-sectional study demonstrated serological evidence of a high rate of exposure to Leptospira spp. among Austrian males [8].

In accordance with the literature exposure to rats or mice has been present in almost 50% of cases of our study cohort [10]. Other important risk exposures included recreational activities in woods or wet areas, gardening as well as cleaning basements or huts. Imported cases were less often icteric and presented with significantly lower transaminase levels when compared to autochthonous cases. This finding is consistent with a previous study of 60 cases of leptospirosis mostly from Germany [2]. In contrast to that study and other reports, we found, however, that in our hospital the number of both imported and autochthonous cases decreased over the study period [2], [10]. While changes in temperature and rainfall may have been contributing factors, the reason for the decrease in autochthonous infections from 2008 to 2009 remains unknown [19].

Another surprising finding was that in our study 39% (95% CI 29–47%) of autochthonous leptospirosis cases occurred in females which stands in contrast to data from Hawaii, the Netherlands and UK where females accounted for less than 10% of leptospirosis cases [9], [10], [12]. In our setting the most frequently identified serogroups were Australis, Sejroe and Icterohaemorrhagiae. In accordance with a previous study from Austria and in contrast to the Netherlands, where the serogroup Canicola had disappeared after 1966, we found four patients autochthonously infected by this serogroup [10]. Two of these four patients had reported contact to dogs prior to occurrence of symptoms.

Acknowledgments

We thank Maria Mueller (AGES) for her help in collecting the MAT results and Christina Strempfl, Bernadette Neuhold and Verena Posch for their support in running Leptospira point-of-care (POC) tests.

Study results were presented in part at ICAAC 2012, San Francisco (poster number 1009), at IMED 2013, Vienna (poster number 21.051) and as oral presentation at ECCMID 2013, Berlin (oral presentation number 333).