FIG. 1.

Addresses, shown as postal codes, for the nine seroresponders to L. pneumophila among the 398 blood donors in the exposed county. Home and workplace addresses are shown within ovals and rectangles, respectively. Seven of the nine seroresponders resided or worked within a range of about 10 km from the city where the outbreak took place (Sarpsborg, Norway), although 2/3 of the exposed blood donors lived in a larger neighbor city (Fredrikstad, Norway) or elsewhere in the county. Different home and workplace addresses for three of the seroresponders are shown by connecting lines. Seroresponders were defined as individuals with positive or borderline IgG and IgM levels by the polyvalent ELISA. The map was created with the ArcGIS 9.2 commercial software program, supplied by Geodata AS (Oslo, Norway).