Danish Ministry of Environment, 2004 15. area. Hence, the high incidence of notified cases in this particular town may not be attributed to an overall increased exposure of the general population. INTRODUCTION and other members of the family Legionellaceae are the causative agents of legionellosis. spp. are aquatic bacteria that can be transmitted to humans by inhalation of water or an aerosol contaminated with the bacteria. The clinical spectrum of legionellosis ranges from asymptomatic infection, through influenza-like disease (Pontiac fever) to Legionnaires’ disease (LD), an often severe pneumonia. infections are underdiagnosed but are nonetheless recognized to be common causes of community-acquired pneumonia [1, 2], in particular in hospitalized patients with exacerbations of chronic obstructive pulmonary disease [3]. LD is a notifiable disease in Denmark, and the incidence is about 20 per million per year; about 50C60% are sporadic community-acquired cases [4]. The incidence of non-pneumonic legionellosis is unknown. The incidence of community-acquired LD is known to vary geographically, and we have shown that a specific town in Denmark, Randers, has a high incidence of LD. It has not been possible to find the cause of this high incidence or otherwise explain the observation [5]. Previous outbreak studies have shown increased antibody levels among individuals exposed to in the population of Randers. The aim of this study was to: (1) describe the geographical variation in the incidence of LD in towns in Denmark, and (2) determine the seroprevalence of antibodies to spp. in the general healthy population in a town with a high incidence of LD and compare the seroprevalence with that of a similar town with an average incidence of LD. METHODS Incidence study Cases of infections were ascertained by reviewing all laboratory tests analysed at Statens Serum Institut from the two counties of Vejle and Aarhus, between July 1996 and June 2002. In addition, we included cases of LD notified by physicians to the Department of Epidemiology, Statens Serum Institut, during the same Rabbit Polyclonal to CLK2 period. A few infections (about 3% of all registered infections in the two counties) were diagnosed at the local microbiology departments [5] and therefore not confirmed by the reference laboratory at the Statens Serum Institut; these cases were therefore not included in our study. Cases were defined according to the definition of a positive laboratory test by Statens Serum Institut (Table 1). Nosocomial and travel-related notified cases, according to the definitions of the European Working Group for Infections, were excluded. Table 1 Laboratory criteria for Sodium formononetin-3′-sulfonate study inclusion Open in a separate window Criteria (1)C(3) are considered as confirmatory of a current or recent infection (Legionnaires’ Sodium formononetin-3′-sulfonate disease in a case of pneumonia). Criteria (4)C(6) are considered as presumptive of a current, recent or past infection (Legionnaires’ disease in a case of pneumonia). By using the Danish Civil Registry number, a unique ID number assigned to all individuals with residence in Denmark, we obtained the addresses of the cases at the time of diagnosis. The addresses were aggregated at the postcode level, and cases were distributed according to seven towns of residence in two neighbouring counties. All towns had a population between 48 000 to 62 000, except Aarhus with a population of about 285 000. Seroepidemiological study Blood samples were collected from 308 healthy blood donors living in the town of Randers (Aarhus County) and 400 healthy blood donors living in Vejle (Vejle County). Blood donors in Denmark are unpaid healthy volunteers aged between 18 and 65 years. The sampling period Sodium formononetin-3′-sulfonate was from late February to early June 2004. No difference was found in sampling frequency between the towns. Sampling took place at the sole hospital in each town. The mean age for the blood donors in Randers and Vejle was 43 and 45 years respectively (in titres* Open in a separate window *The titres are based on the highest titre to any antigen in each case. The blood samples were analysed for antibodies to spp. by indirect immunofluorescence antibody test (IFAT) with plate-grown and heat-inactivated serogroup (sg) 1C6 and and as antigens. The serum samples were titrated from 1:64 and upwards. Antibodies to spp. were detected with a FITC conjugated rabbit anti-human IgM, A and G antibody (Code F0200, Dako, Glostrup, Denmark). An blocking fluid was used to block cross-reacting antibodies to Gram-negative bacteria [9]. Samples with an antibody titre of ?1:128 were considered as positive for laboratory test (). 1, Kolding; 2, Fredericia; 3, Vejle; 4, Horsens; 5, Aarhus; 6, Silkeborg; 7, Randers. Seroprevalence of antibodies to in healthy blood donors In Randers, 62 (201%) of 308 donors had IFAT titres of ?1:128, compared with 101 (253%) of 400 donors from Vejle (risk ratio 080, 95% CI 060C105, seroprevalence in the study population () compared to the distribution.