Incidence and geographic distribution of serologically verified cases of nephropathia epidemica in Sweden.

A nationwide survey of hospitalized, serologically verified adult nephropathia epidemica cases in Sweden from 1978 to 1981 was performed. Serum was collected from 1,063 patients with a diagnosis of nephropathia epidemica or one of 10 other renal diseases with related symptoms. Sera were analyzed by indirect immunofluorescence technique for the presence of immunoglobulin G antibodies to Hantaan virus, causative agent of Korean hemorrhagic fever that cross-reacts with the nephropathia epidemica agent. Antibodies were present in 368 patients, 355 of whom also fulfilled four or more of six criteria for clinical diagnosis of nephropathia epidemica. The male:female ratio was 2.7:1. The total number of cases in Sweden varied between 26 and 144 per year, which coincided with the fluctuations in small rodent populations. The highest incidence was found in Västerbotten County, with a maximum crude incidence rate of 23.5 cases per 100,000 inhabitants per year. Mean crude incidence in Sweden during the study period was 1.3 cases per 100,000 inhabitants per year. The southernmost cases lived in proximity to the 59th parallel. Thus, nephropathia epidemica was found to be prevalent south of the 60th parallel, which was previously assumed to be its southern boundary.