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Landscape epidemiology of tularemia outbreaks in Sweden.

Svensson K, Bäck E, Eliasson H, Berglund L, Granberg M, Karlsson L, Larsson P, Forsman M, Johansson A - Emerging Infect. Dis. (2009)

Bottom Line: Strong spatial associations were found between F. tularensis subpopulations and the places of disease transmission; infection by some subpopulations occurred within areas as small as 2 km(2), indicating unidentified environmental point sources of tularemia.In both locations, disease clusters were associated with recreational areas beside water, and genetic subpopulations were present throughout the tularemia season and persisted over years.High-resolution genotyping in combination with patients' statements about geographic places of disease transmission provided valuable indications of likely sources of infection and the causal genotypes during these tularemia outbreaks.

View Article: PubMed Central - PubMed

Affiliation: Swedish Defense Research Agency, Umea, Sweden.

ABSTRACT
Summer outbreaks of tularemia that occurred from 1995 through 2005 in 2 locations in Sweden affected 441 persons. We performed an epidemiologic investigation of these outbreaks using a novel strategy, involving high-resolution genotyping of Francisella tularensis isolates obtained from 136 patients (using 18 genetic markers developed from 6 F. tularensis genome sequences) and interviews with the patients. Strong spatial associations were found between F. tularensis subpopulations and the places of disease transmission; infection by some subpopulations occurred within areas as small as 2 km(2), indicating unidentified environmental point sources of tularemia. In both locations, disease clusters were associated with recreational areas beside water, and genetic subpopulations were present throughout the tularemia season and persisted over years. High-resolution genotyping in combination with patients' statements about geographic places of disease transmission provided valuable indications of likely sources of infection and the causal genotypes during these tularemia outbreaks.

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A) Directional distributions of tularemia transmission sites in Ljusdal, Sweden, by outbreak year (red ellipses). The Francisella tularensis isolates recovered from patients in Ljusdal were genetically monomorphic, with 53/56 isolates belonging to genetic subgroup 1e (solid black ellipse). The dashed black ellipse represents the distributions of all 56 isolates. Each ellipse represents a 1 standard deviation distribution around the mean centers of occurrence (starred). B) Distributions of 13 isolates of genetic group 1e, genotype identification (ID) 15 (red), Ljusdal, 1995. C) Distributions of 26 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black), Ljusdal, 1998. Numbers above symbols indicate multiple data points. D) Distributions of 13 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black); genetic group 1b (green); genetic group 1c (gray); and genetic group 3 (white), Ljusdal, 2005. Spatial data quality assessment for each pair of coordinates is shown as certain (circle), probable (square), or possible (diamond); patient residency (triangle) was used when transmission data were unavailable.
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Figure 7: A) Directional distributions of tularemia transmission sites in Ljusdal, Sweden, by outbreak year (red ellipses). The Francisella tularensis isolates recovered from patients in Ljusdal were genetically monomorphic, with 53/56 isolates belonging to genetic subgroup 1e (solid black ellipse). The dashed black ellipse represents the distributions of all 56 isolates. Each ellipse represents a 1 standard deviation distribution around the mean centers of occurrence (starred). B) Distributions of 13 isolates of genetic group 1e, genotype identification (ID) 15 (red), Ljusdal, 1995. C) Distributions of 26 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black), Ljusdal, 1998. Numbers above symbols indicate multiple data points. D) Distributions of 13 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black); genetic group 1b (green); genetic group 1c (gray); and genetic group 3 (white), Ljusdal, 2005. Spatial data quality assessment for each pair of coordinates is shown as certain (circle), probable (square), or possible (diamond); patient residency (triangle) was used when transmission data were unavailable.

Mentions: The F. tularensis isolates recovered from 1995 through 2005 from patients in Ljusdal were genetically monomorphic. The 53 of 56 isolates that belonged to genetic subgroup 1e were circumscribed by a 150-km2 ellipse (Figure 7, panel A). All 56 isolates were circumscribed by a 230-km2 ellipse. Analysis per outbreak year showed that the infection area of 1e isolates was stable, with an east–west distribution along the river Ljusnan (Figure 7). The places of disease transmission for 3 isolates of genetic subgroups 1b, 1c, and 3 were peripheral to the infection area of 1e isolates (Figure 7, panel D). Many patients reported acquiring tularemia from restricted geographic areas, e.g., 33 of 56 isolates were from a 25-km2 stretch along the river Ljusnan, with a disease cluster at a golf course (Figure 2).


Landscape epidemiology of tularemia outbreaks in Sweden.

Svensson K, Bäck E, Eliasson H, Berglund L, Granberg M, Karlsson L, Larsson P, Forsman M, Johansson A - Emerging Infect. Dis. (2009)

A) Directional distributions of tularemia transmission sites in Ljusdal, Sweden, by outbreak year (red ellipses). The Francisella tularensis isolates recovered from patients in Ljusdal were genetically monomorphic, with 53/56 isolates belonging to genetic subgroup 1e (solid black ellipse). The dashed black ellipse represents the distributions of all 56 isolates. Each ellipse represents a 1 standard deviation distribution around the mean centers of occurrence (starred). B) Distributions of 13 isolates of genetic group 1e, genotype identification (ID) 15 (red), Ljusdal, 1995. C) Distributions of 26 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black), Ljusdal, 1998. Numbers above symbols indicate multiple data points. D) Distributions of 13 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black); genetic group 1b (green); genetic group 1c (gray); and genetic group 3 (white), Ljusdal, 2005. Spatial data quality assessment for each pair of coordinates is shown as certain (circle), probable (square), or possible (diamond); patient residency (triangle) was used when transmission data were unavailable.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3044527&req=5

Figure 7: A) Directional distributions of tularemia transmission sites in Ljusdal, Sweden, by outbreak year (red ellipses). The Francisella tularensis isolates recovered from patients in Ljusdal were genetically monomorphic, with 53/56 isolates belonging to genetic subgroup 1e (solid black ellipse). The dashed black ellipse represents the distributions of all 56 isolates. Each ellipse represents a 1 standard deviation distribution around the mean centers of occurrence (starred). B) Distributions of 13 isolates of genetic group 1e, genotype identification (ID) 15 (red), Ljusdal, 1995. C) Distributions of 26 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black), Ljusdal, 1998. Numbers above symbols indicate multiple data points. D) Distributions of 13 isolates of genetic group 1e, genotype ID 15 (red) and genotype ID 16 (black); genetic group 1b (green); genetic group 1c (gray); and genetic group 3 (white), Ljusdal, 2005. Spatial data quality assessment for each pair of coordinates is shown as certain (circle), probable (square), or possible (diamond); patient residency (triangle) was used when transmission data were unavailable.
Mentions: The F. tularensis isolates recovered from 1995 through 2005 from patients in Ljusdal were genetically monomorphic. The 53 of 56 isolates that belonged to genetic subgroup 1e were circumscribed by a 150-km2 ellipse (Figure 7, panel A). All 56 isolates were circumscribed by a 230-km2 ellipse. Analysis per outbreak year showed that the infection area of 1e isolates was stable, with an east–west distribution along the river Ljusnan (Figure 7). The places of disease transmission for 3 isolates of genetic subgroups 1b, 1c, and 3 were peripheral to the infection area of 1e isolates (Figure 7, panel D). Many patients reported acquiring tularemia from restricted geographic areas, e.g., 33 of 56 isolates were from a 25-km2 stretch along the river Ljusnan, with a disease cluster at a golf course (Figure 2).

Bottom Line: Strong spatial associations were found between F. tularensis subpopulations and the places of disease transmission; infection by some subpopulations occurred within areas as small as 2 km(2), indicating unidentified environmental point sources of tularemia.In both locations, disease clusters were associated with recreational areas beside water, and genetic subpopulations were present throughout the tularemia season and persisted over years.High-resolution genotyping in combination with patients' statements about geographic places of disease transmission provided valuable indications of likely sources of infection and the causal genotypes during these tularemia outbreaks.

View Article: PubMed Central - PubMed

Affiliation: Swedish Defense Research Agency, Umea, Sweden.

ABSTRACT
Summer outbreaks of tularemia that occurred from 1995 through 2005 in 2 locations in Sweden affected 441 persons. We performed an epidemiologic investigation of these outbreaks using a novel strategy, involving high-resolution genotyping of Francisella tularensis isolates obtained from 136 patients (using 18 genetic markers developed from 6 F. tularensis genome sequences) and interviews with the patients. Strong spatial associations were found between F. tularensis subpopulations and the places of disease transmission; infection by some subpopulations occurred within areas as small as 2 km(2), indicating unidentified environmental point sources of tularemia. In both locations, disease clusters were associated with recreational areas beside water, and genetic subpopulations were present throughout the tularemia season and persisted over years. High-resolution genotyping in combination with patients' statements about geographic places of disease transmission provided valuable indications of likely sources of infection and the causal genotypes during these tularemia outbreaks.

Show MeSH
Related in: MedlinePlus