leptospirosis a common and dreaded zoonosis of global distribution , caused by infection with pathogenic spirochetes of the genus leptospira . the disease is maintained in nature by chronic renal infection of carrier animals , which excrete the organism in their urine , contaminating the environment . human infection occurs by direct contact with infected urine or tissues or , more commonly by indirect exposure to the organism in damp soil or water . the serovar classification remains useful for epidemiological purposes , as many geographically widespread serovar - reservoir associations exist . according to recent studies on the worldwide incidence of leptospirosis , croatia is 13 in the world and 1 in europe , with an incidence rate of 17.3 cases per million population annually . leptospirosis is endemic in croatia , and most commonly occurs in the sava and drava river valleys of central and northwestern croatia and in the neretva river valley [ 812 ] . leptospirosis in croatia has been systematically monitored and studied for more than 50 years , as a constant object of investigation of infectious disease specialists , epidemiologists , immunologists , veterinarians and foresters . throughout this time no changes were observed in the incidence rates of leptospirosis in humans and wild animals ; however , changes in the incidence rates have been observed among the most likely infectious serovars . molecular analysis of leptospira spp . the highest incidence in the last 10 years has been observed among the following serovars : leptospira interrogans serovar australis , leptospira kirschneri serovar grippotyphosa and leptospira interrogans serovar saxkoebing , as opposed to france , italy and germany where leptospira interrogans serovar icterohaemorrhagiae is the most common serovar causing infections in humans [ 5,1316 ] . the severity of leptospiral infections ranges from a subclinical illness to 2 clinically recognizable syndromes : a self limited , systemic illness seen in approximately 90% of infections , and a severe potentially fatal illness accompanied by any combination of renal failure , liver failure , pneumonitis with hemorrhagic diathesis and myocarditis . death , occurring in 1015% of these severe cases , is usually due to pulmonary hemorrhage , renal failure or cardiac failure and arrhythmia secondary to myocarditis . the finding of ecg abnormalities in patients with leptospirosis who show clinical evidence of cardiac involvement is well recognized . clinical reports make it clear that pericarditis , endocarditis , myocarditis and arrhythmias occur in leptospirosis . a few systematic studies of latent cardiac involvement in leptospirosis have been made [ 2124 ] . experimental studies in animals and autopsies in humans have shown that cardiac involvement in leptospirosis is frequent , even though it may occur without clinical manifestations . the aim of this study was to investigate the incidence and type of ecg changes in patients with leptospirosis regardless of clinical evidence of cardiac involvement . the ethics committee of the university hospital for infectious diseases  dr fran mihaljevi , zagreb , croatia ( uhid ) approved the study . a total of 97 patients with serologically confirmed leptospirosis treated at the university hospital for infectious diseases  dr . fran mihaljevi ( uhid ) in zagreb , croatia , which is the national reference centre for infectious diseases , were included in this retrospective study from 2000 to 2009 . in the investigated period there were 213 hospitalized patients with clinical and epidemiological diagnosis of leptospirosis , which was serologically confirmed in 105 ( 1 patient with known heart disease was excluded and 7 medical history charts were unavailable ) . epidemiological and clinical data including main clinical characteristics and laboratory findings were obtained from hospital charts . the diagnosis was confirmed by microscopic agglutination test ( mat ) performed at the laboratory for leptospires , department of microbiology and infectious diseases clinic , faculty of veterinary medicine , university of zagreb ( 20002008 ) and leptospira laboratory at the croatian national institute of public health ( 20082009 ) , with 12 leptospira serovars : leptospira kirschneri serovar grippotyphosa , leptospira interrogans serovar sejroe , leptospira interrogans serovar australis , leptospira interrogans serovar pomona , leptospira interrogans serovar canicola , leptospira interrogans serovar icterohaemorrhagiae , leptospira interrogans serovar tarassovi , leptospira interrogans serovar saxkoebing , leptospira interrogans serovar ballum , leptospira interrogans serovar bataviae , leptospira borgpetersenii serovar poi and leptospira interrogans serovar hardjo . a cut - off value of 1:500 was used for a significant titre in patients in whom those with at least a 4-fold increase in titre were considered positive . in case of coagglutination , the serovar with the most expressed increase in antibody titre was accepted as pathogenic , and if antibody titers were equal , the finding was accepted as undetermined . a 12-lead resting ecg was routinely performed in the first 2 days after hospital admission independent of the clinical manifestations of patients and prior to antibiotic administration . we considered all nonspecific st segment and t wave abnormalities to be non - specific ventricular repolarization disturbances . thorough past and current medical history was obtained , and careful physical examination and laboratory tests were performed . exclusion criteria were as follows : prior known alterations in ecg finding , and prior intake of drugs that can influence ecg finding . the variables recorded in each patient included sex , age , duration of disease prior to admission , duration of hospitalization , chest x - ray , white blood cell count , platelets , c - reactive protein , serum creatinine , potassium , alanine aminotransferase , aspartate aminotransferase , bilirubin and urine . we describe our data with medians and interquartile range for continuous variables , and frequencies for categorical variables . the main clinical characteristics and laboratory findings of patients with normal and abnormal ecg were compared by the chi - square or wilcoxon rank - sum test . all tests were performed with the sas software system release 9.1.3 ( sas institute , cary , nc ) . we describe our data with medians and interquartile range for continuous variables , and frequencies for categorical variables . the main clinical characteristics and laboratory findings of patients with normal and abnormal ecg were compared by the chi - square or wilcoxon rank - sum test . all tests were performed with the sas software system release 9.1.3 ( sas institute , cary , nc ) . abnormal ecg findings were found in 56 of 97 ( 58% ) patients with serologically confirmed leptospirosis hospitalized at the university hospital for infectious diseases in zagreb , croatia from 2000 to 2009 . the majority of patients were hospitalized from july to october ( 68/97  70% ) and the majority had positive epidemiological anamnesis ( 90/97  93% ) . there were no differences in age , sex , duration of symptoms prior to admission or hospital stay between the patients with normal and abnormal ecg ( table 1 ) . the incidence of certain clinical symptoms did not differ with regards to ecg changes ( table 2 ) , nor were there statistical differences in white blood cell count , creatinine , c - reactive protein , and aspartate aminotransferase . patients with abnormal ecg had significantly elevated values of bilirubin and alanine aminotransferase , lower values of potassium and lower number of platelets , as well as more frequently recorded abnormal chest x - ray . ecg was recorded in all patients in the first 2 days after hospitalization when patients were febrile . non - specific ventricular repolarization disturbances were the most common abnormal ecg finding ( figure 1 ) . other recorded ecg abnormalities were sinus tachycardia , right branch conduction disturbances , low voltage of the qrs complex in standard limb leads , supraventricular and ventricular extrasystoles , intraventricular conduction disturbances , atrioventricular block first - degree and atrial fibrillation . myopericarditis was identified in 4 patients on the basis of physician examination ( muffled first heart sound ) , ecg findings ( non - specific st segment and t wave abnormalities , tachycardia , arrhythmias ) and echocardiography ( table 3 ) . in our patients , serovar australis , leptospira interrogans serovar saxkoebing and leptospira kirschneri serovar grippotyphosa ( table 4 ) . electrocardiographic findings of transient changes found on routine ecg in patients with uncomplicated leptospirosis confirm the predictions of first researchers [ 1921 ] that ecg evidence of cardiac involvement may be found in the absence of physical signs . the first systematic comparative research of ecg findings in a total of 43 patients with leptospirosis and malaria hospitalized from 1960 to 1962 in the british military hospital in malaga and in healthy persons exposed to artificial hyperpyrexia showed that transient ecg abnormalities are similar in patients with leptospirosis and malaria and are nonspecific results of a febrile infection . electrocardiographic alterations were detected in 68% of 157 patients hospitalized with leptospirosis in salvador , brazil from 1998 to 1999 . atrial fibrillation occurred in 11% , and alterations in ventricular repolarization occurred in 39% of patients . the patients with atrial fibrillation were older , had higher levels of creatinine and aminotransferases , and had evidence of more severe disease . the mechanisms determining the ecg alterations were not specifically assessed in the study , nor was the relation between the presence and type of ecg alteration and the prognosis of leptospirosis . the clinical picture of anicteric leptospirosis can closely mimic that of hemorrhagic fever with renal syndrome ( hfrs ) . both diseases predominantly affect farmers , trappers , veterinarians and military personnel who may have contact with infected animals or their urine . both diseases are acute febrile diseases most commonly affecting the kidneys , and cause pulmonary and liver disorders as well as ecg abnormalities . although there is no curative therapy for hfrs , antibiotic therapy for leptospirosis is generally believed to be beneficial if initiated early in the course of the disease . therefore , it is important to introduce rapid tests for the detection of both diseases , especially in endemic regions . a total of 1208 patients with serologically confirmed leptospirosis were hospitalized at uhid in the period 19471979 . in all patients ecg was performed ; however , no subclinical transitory ecg abnormalities were recorded . several published case reports of patients with clinically severe forms of leptospirosis hospitalized in uhid also reported no ecg abnormalities [ 3436 ] . a total of 256 patients with serologically confirmed leptospirosis hospitalized at uhid from 1973 to 1982 were evaluated retrospectively . the purpose of the study was to estimate the incidence of sporadic clinical manifestations in leptospirosis such as electrocardiographic changes . nonspecific alterations of the ventricular repolarization were found most often ( 23 patients ) , while atrial fibrillation was recorded in 2 patients . in patients with ecg changes , the most frequently observed pathogens were leptospira interrogans serovar icterohaemorrhagiae ( 20 ) , leptospira kirschneri serovar grippotyphosa ( 12 ) and leptospira interrogans serovar sejroe ( 6 ) . among 130 retrospectively analyzed patients with serologically confirmed leptospirosis hospitalized at uhid in the period from 1997 to 2007 , 9 ( 7% ) patients developed weil s disease and were treated at the intensive care unit . three patients had acute myopericarditis , and 1 of them developed atrial fibrillation , all with a benign clinical course . we retrospectively analyzed 213 hospitalized patients with clinical and epidemiological diagnosis of leptospirosis which was serologically confirmed in less than half of the patients . although in endemic areas , the classic history of fever , myalgia and headache in patients with positive epidemiological anamnesis should raise the possibility of leptospirosis , it should be confirmed by serology . this is supported by research from iran , where out of a total of 237 patients with clinically and epidemiologically suspected leptospirosis , the diagnosis was confirmed in 74 . electrocardiograms in our patients were performed in the first 2 days after hospital admission , independent of the clinical manifestations of the patients and prior to antibiotic administration . all patients were febrile at admission and all developed a moderately severe form of disease requiring symptomatic treatment . atrial fibrillation occurred in 6 patients , 1 of whom also had right bundle branch conduction disturbances , and 4 also had non - specific ventricular repolarization disturbances . in 36 patients control ecgs were performed during hospitalization which proved normal or improved except in 4 patients with atrial fibrillation which did not regress during hospitalization . these patients probably had cardiac predisposition and clinical cardiac manifestation was incited by leptospirosis . in patients with and without ecg changes , the following serovars were most frequently detected : leptospira interrogans serovar australis , leptospira interrogans serovar saxkoebing and leptospira kirschneri serovar grippotyphosa . ecg alterations and heart disorders indicate that leptospiras may exhibit tropism for myocardium and contribute directly or indirectly to cardiac disorders during mild , moderate or severe forms of leptospirosis . the presence of transient ecg abnormalities such as sinus tachycardia , non - specific ventricular repolarization disturbances , bundle branch or ventricular conduction disturbances and atrial fibrillation are common at the beginning of disease and possibly are caused by the direct effect of leptospires or febrile infection with a combination of metabolic and electrolyte abnormalities . further research is required for better understanding of the pathogenesis of leptospiral infections and the mechanism of electrocardiographic alterations in leptospirosis , and to explore the possible relationship between electrocardiographic alterations and the prognosis of leptospirosis .
summarybackgroundthe aim of this study was to investigate the incidence and type of ecg changes in patients with leptospirosis regardless of clinical evidence of cardiac involvement.material/methodsa total of 97 patients with serologically confirmed leptospirosis treated at the university hospital for infectious diseases  dr . 
 fran mihaljevi in zagreb , croatia , were included in this retrospective study . 
 a 12-lead resting ecg was routinely performed in the first 2 days after hospital admission . 
 thorough past and current medical history was obtained , and careful physical examination and laboratory tests were performed.resultsabnormal ecg findings were found in 56 of 97 ( 58% ) patients . 
 patients with abnormal ecg had significantly elevated values of bilirubin and alanine aminotransferase , lower values of potassium and lower number of platelets , as well as more frequently recorded abnormal chest x - ray . 
 non - specific ventricular repolarization disturbances were the most common abnormal ecg finding . 
 other recorded ecg abnormalities were sinus tachycardia , right branch conduction disturbances , low voltage of the qrs complex in standard limb leads , supraventricular and ventricular extrasystoles , intraventricular conduction disturbances , atrioventricular block first - degree and atrial fibrillation . 
 myopericarditis was identified in 4 patients . 
 regardless of ecg changes , the most commonly detected infection was with leptospira interrogans 
 serovar australis , leptospira interrogans serovar saxkoebing and leptospira kirschneri serovar grippotyphosa.conclusionsthe ecg abnormalities are common at the beginning of disease and are possibly caused by the direct effect of leptospires or are the non - specific result of a febrile infection and metabolic and electrolyte abnormalities . 
 new studies are required for better understanding of the mechanism of ecg alterations in leptospirosis .