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clinicians and microbiologic laboratories report diagnosed cases to the swedish institute for infectious disease control .
, we included all 5,282 ne cases reported to the swedish institute for infectious disease control and registered in the database during january 1 , 1997december 31 , 2007 .
openepi ( www.openepi.com ) was used to calculate the standardized mortality ratio ( smr ) . because ne is an acute viral infection , and as a comparison for the numbers of deaths during the different phases of ne
, we used the number of deaths during the second year after diagnosis in the studied population .
incidence was highest in the group 5559 years of age for men and women ( figure 1 , panel a ) , and the mean  sd age at diagnosis was 49.3  16.7 years for men and 50.7  16.5 years for women .
sex hormones can play major roles in susceptibility to infectious diseases ( 5,7 ) . to test whether increased incidence of puuv infection in men was dependent on sex hormones , we compared sex ratios in ne cases between children ( persons < 10 years of age and presumably prepubertal ) and adults ( > 10 years of age ) .
the male : female ratio for these children was 1.58:1 , which was similar to the sex ratio for adult ne patients ( 1.52:1 ) .
this finding suggested that circulating sex hormones may not play a major role in the observed overrepresentation of ne in men .
incidence of acute nephropathia epidemica ( ne ) and case - fatality rates , sweden , 19972007 . a ) age distribution for male and female patients with acute ne .
b ) age distribution of case - fatality rates for all patients with acute ne .
the swedish death register was used to identify all deceased persons with a diagnosis of ne .
numbers of deaths during different periods after diagnoses were 21 ( 13 male patients and 8 female patients ) during the acute phase ( <3 months after diagnoses ) , 7 ( 5 male patients and 2 female patients ) after the acute phase ( > 3 months after diagnoses ) but < 1 year later , and 24 ( 19 male patients and 5 female patients ) during the second year after diagnoses . of persons with a diagnosis of ne , 21 ( 0.4% )
the smr was 3.5 ( 95% confidence interval [ ci ] 2.225.26 ) for all patients and 6.4 ( 95% ci 2.9712.15 ) for female patients and 2.7 ( 95% ci 1.524.56 ) for male patients during the acute phase of ne .
no persons < 50 years of age died during the acute phase ( figure 1 , panel b ) .
however , the case - fatality rate increased with age ( figure 1 , panel b ) , and the case - fatality rate was 6.5% for patients
> 80 years of age , which showed age - dependent differences in mortality rates for ne .
the mean  sd age at time of death for patients with acute ne was 73.7  10.4 years ( range 50.988.5 years ) .
women died at a slightly , but not significantly , younger mean  sd age ( 71.5  12.4 years , range 50.985.7 years , n = 8) than men ( 75.1  9.2 years , range 57.888.5 years , n = 13 ) ( p = 0.347 , by t test ) . mean age at time of death for patients with ne was 10 years less than the expected life span for women and 3 years less than the expected life span for men ( mean age at time of death in sweden in 2003 was 78 years for men and 82 years for women ; www.scb.se/statistik/_publikationer/be0701_1986i03_br_be51st0404.pdf ) .
because no patient < 50 years of age died of ne during the acute phase and the mean age at time of death was relatively high , we suggest that ne is rarely life threatening . to assess this possibility , we analyzed mortality rate patterns early after acute ne .
the smr decreased for the 9 months after acute ne in female ( smr 0.67 , 95% ci 0.112.20 ) and male ( smr 0.36 , 95% ci 0.130.79 ) patients ( figure 2 ) .
overall standardized mortality ratios ( smrs ) for male and female patients with a diagnosis of acute nephropathia epidemica ( ne ) and smrs 312 mo after diagnosis , sweden , 19972007 .
we also analyzed smrs for the first year ( including the acute phase of ne [ <3 months after diagnosis ] and early phase [ 312 months ] after ne diagnosis ) . for 52 persons who died < 2 years after ne diagnosis ,
the case - fatality rate was only slightly higher in the first year ( n = 28 ) than in the second year ( n = 24 ) after diagnosis ( smr 1.17 , 95% ci 0.791.66 ) .
deaths did not increase in men between the first ( n = 18 ) and second ( n = 19 ) years after diagnosis ( smr 0.95 , 95% ci 0.581.49 ) .
however , we observed a 2 difference in deaths for women between the first ( n = 10 ) and second ( n = 5 ) years after diagnosis ( smr 2.0 , 95% ci 1.023.57 ) .
we report an age - dependent case - fatality rate for the hantavirus disease ne ; most deaths occurred in older persons .
there is a report of patients < 50 years of age dying of ne ( 12 ) , but this finding is rare .
increased case - fatality rates in older persons have been described for other infectious diseases .
for example , during a typical influenza season , 90% of deaths caused by influenza occur among persons > 65 years of age ( 13 ) .
whether this finding is unique to relatively mild infection with puuv or is a conserved feature of all hantaviruses causing hfrs / hcps is unknown .
we previously showed that there are sex differences in cytokine responses during acute ne ( 11 ) , which suggested that there might be sex differences in severity of infection .
women showed a 2 difference in number of deaths between the first year and second year after ne diagnosis .
however , men showed no difference in number of deaths between the first year and second year after diagnosis .
these results suggest that there are sex differences in mortality rates after infection with puuv .
whether ne is a more lethal disease in women than men or causes increased mortality rates in men up to 2 years after diagnoses is unknown .
the finding that the case - fatality rate for ne is associated with the age and sex of patients might have practical implications on healthcare issues .
it may also indicate that age and sex should be considered predictive variables in clinical studies of hantavirus infections .
to investigate nephropathia epidemica in sweden during 19972007 , we determined case - fatality rates for 5,282 patients with this disease . overall , 0.4% died of acute nephropathia epidemica <3 months after diagnosis . 
 case - fatality rates increased with age . 
 only women showed an increased case - fatality rate during the first year after diagnosis .