| 1. |
- Boqvist, Sofia, et al.
(författare)
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Sources of sporadic Yersinia enterocilitica infection in children in Sweden, 2004 : a case-control study
- 2009
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Ingår i: Epidemiology and Infection. - 0950-2688 .- 1469-4409. ; 137, s. 897-905
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Tidskriftsartikel (refereegranskat)abstract
- Young children account for a large proportion of reported Yersinia enterocolitica infections in Sweden with a high incidence compared with other gastrointestinal infections, such as salmonellosis and campylobacteriosis. A case-control study was conducted to investigate selected risk factors for domestic sporadic yersiniosis in children aged 0–6 years in Sweden. In total, 117 cases and 339 controls were included in the study. To minimize exclusion of observations due to missing data a multiple non-parametric imputation technique was used. The following risk factors were identified in the multivariate analysis : eating food prepared from raw pork products (OR 3.0, 95% CI 1.8–5.1) or treated sausage (OR 1.9, 95% CI 1.1–3.3), use of a baby’s dummy (OR 1.9, 95% CI 1.1–3.2) and contact with domestic animals (OR 2.0, 95% CI 1.2–3.4). We believe that the importance of Y. enterocolitica infection in children has been neglected and that results from this study can be used to develop preventive recommendations.
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| 2. |
- Camitz, Martin, et al.
(författare)
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The effect of time distribution shape on a complex epidemic model
- 2009
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Ingår i: Bulletin of Mathematical Biology. - : Springer Science and Business Media LLC. - 0092-8240 .- 1522-9602. ; 71:8, s. 1902-1913
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Tidskriftsartikel (refereegranskat)abstract
- In elaborating a model of the progress of an epidemic, it is necessary to make assumptions about the distributions of latency times and infectious times. In many models, the often implicit assumption is that these times are independent and exponentially distributed. We explore the effects of altering the distribution of latency and infectious times in a complex epidemic model with regional divisions connected by a travel intensity matrix. We show a delay in spread with more realistic latency times. More realistic infectiousness times lead to faster epidemics. The effects are similar but accentuated when compared to a purely homogeneous mixing model.
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| 3. |
- Ejlertsson, Jörgen, et al.
(författare)
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Anaerobic Degradation of Nonylphenol Mono- and Diethoxylates in Digestor Sludge, Landfilled Municipal Solid Waste, and Landfilled Sludge
- 1999
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 1086-931X .- 1520-6912 .- 0013-936X .- 1520-5851. ; 33:2, s. 301-306
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the extent to which anaerobic digestor sludge, landfilled sludge, and landfilled municipal solid waste (MSW) degrade NPEOs under methanogenic conditions. NPEO1 and NPEO2 (NPEO1-2), used in a mixture, were chosen as model compounds. Anaerobic experimental bottles were amended with 100% digestor sludge at three different concentrations of NPEO1-2: 2, 60, and 308 mg L-1. [U-14C]-NPEO1-2 was used to detect any possible decomposition of the aromatic moiety of the NPEO1-2. All inoculates used degraded NPEO1-2 at 2 mg L-1, with nonylphenol (NP) forming the ultimate degradation product. The NP formed was not further degraded, and the incubations with labeled NPEO showed that the aromatic structure remained intact. Both landfill inoculates also transformed NPEO1-2 at 60 mg L-1. CH4 production was temporarily hampered in bottles with MSW landfill inoculum at 60 and 308 mg L-1. With 2 mg L-1 of NPEO, CH4 production closely followed that in the controls. Both NP and NPEO1-2 interacted with the organic matter which resulted in sorption to the solid phase.
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| 4. |
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| 5. |
- Svensson, Bo, 1946-, et al.
(författare)
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Anaerobic digestion of alfalfa silage with recirculation of process liquid
- 2007
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 98:1, s. 104-111
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Tidskriftsartikel (refereegranskat)abstract
- Process liquid recirculation initially stimulated one-phase anaerobic digestion of alfalfa silage in two semi-continuously fed and stirred tank reactors. Thus, with increased pH, alkalinity and stability it was possible to increase the organic loading rate to 3 g VS L-1 d-1, as compared to 2.25 g VS L-1 d-1 in a control reactor without recirculation. However, the recirculation of liquid eventually caused an accumulation of organic and inorganic substances, leading to an inhibition of hydrolysis and methanogenesis. This inhibition of microbial activity was prevented in one of the processes by replacing 50% of the recirculated process liquid with water during the second half of the operation period. A multiple linear regression model of principal components using seven input variables explained the variance in output variables nearly as well as the original model using all 23 measured input variables. The results show that it is necessary to adjust the degree of liquid recirculation to reach an optimal process. © 2005 Elsevier Ltd. All rights reserved.
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| 6. |
- Svensson, Åke, 1946-
(författare)
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Goodness-of-fit tests for some discrete multiplicative models with applications to road traffic accident analysis
- 1979
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in the thesis was initiated by some problems in the analysis of experiments concerning the effect of speed limits on the number of road traffic accidents. In order to do such an analysis realistic statistical models are required. A class of discrete multiplicative models is used to describe the variations in the number of accidents. A goodness-of-fit test for the models is suggested and an approximation of the test in a relevant asymptotic situation is derived. This derivation is based on a conditional limit theorem. The models are applied to two road safety problems. The first problem concerns the effect of speed limits and the second problem the relation between traffic flow and accident types.
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| 7. |
- Svensson, Åke, 1946-
(författare)
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The influence of assumptions on generation time distributions in epidemic models
- 2015
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Ingår i: Mathematical Biosciences. - : Elsevier BV. - 0025-5564 .- 1879-3134. ; 270:Part A, s. 81-89
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Tidskriftsartikel (refereegranskat)abstract
- A simple class of stochastic models for epidemic spread in finite, but large, populations is studied. The purpose is to investigate how assumptions about the times between primary and secondary infections influences the outcome of the epidemic. Of particular interest is how assumptions of individual variability in infectiousness relates to variability of the epidemic curve. The main concern is the final size of the epidemic and the time scale at which it evolves. The theoretical results are illustrated by simulations.
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| 8. |
- Svensson, Åke, 1946-
(författare)
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Who was the infector-probabilities in the presence of variability in latent and infectious times.
- 2013
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Ingår i: Journal of Mathematical Biology. - : Springer. - 0303-6812 .- 1432-1416. ; 68:4, s. 951-967
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Tidskriftsartikel (refereegranskat)abstract
- The probability that an observed infection has been transmitted from a particular member of a set of potential infectors is calculated. The calculations only use knowledge of the times of infection. It is shown that the probabilities depend on individual variability in latent and infectious times. The analysis are based on different background information and different assumptions on the progress of infectivity. The results are illustrated by numerical calculations and simulations.
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| 9. |
- Törner, Anna, et al.
(författare)
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A method to visualize and adjust for selection bias in prevalent cohort studies
- 2011
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Ingår i: American Journal of Epidemiology. - : Oxford University Press (OUP). - 0002-9262 .- 1476-6256. ; 174:8, s. 969-76
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Tidskriftsartikel (refereegranskat)abstract
- Selection bias and confounding are concerns in cohort studies where the reason for inclusion of subjects in the cohort may be related to the outcome of interest. Selection bias in prevalent cohorts is often corrected by excluding observation time and events during the first time period after inclusion in the cohort. This time period must be chosen carefully-long enough to minimize selection bias but not too long so as to unnecessarily discard observation time and events. A novel method visualizing and estimating selection bias is described and exemplified by using 2 real cohort study examples: a study of hepatitis C virus infection and a study of monoclonal gammopathy of undetermined significance. The method is based on modeling the hazard for the outcome of interest as a function of time since inclusion in the cohort. The events studied were "hospitalizations for kidney-related disease" in the hepatitis C virus cohort and "death" in the monoclonal gammopathy of undetermined significance cohort. Both cohorts show signs of considerable selection bias as evidenced by increased hazard in the time period after inclusion in the cohort. The method was very useful in visualizing selection bias and in determining the initial time period to be excluded from the analyses.
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| 10. |
- Törner, Anna, et al.
(författare)
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A proposed method to adjust for selection bias in cohort studies
- 2010
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Ingår i: American Journal of Epidemiology. - : Oxford University Press (OUP). - 0002-9262 .- 1476-6256. ; 171:5, s. 602-608
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Tidskriftsartikel (refereegranskat)abstract
- Selection bias is a concern in cohort studies in which selection into the cohort is related to the studied outcome. An example is chronic infection with hepatitis C virus, where the initial infection may be asymptomatic for decades. This problem leads to selection of more severely ill individuals into registers of such infections. Cohort studies often adjust for this bias by introducing a time window between entry into the cohort and entry into the study. This paper describes and assesses a novel method to improve adjustment for this type of selection bias. The size of the time window is decided by calculating a standardized incidence ratio as a continuous function of the size of the time window. The resulting graph is used to decide on an appropriate window size. The method is evaluated by using the Swedish register of hepatitis C virus infections for 1990-2006. The complications studied were non-Hodgkin lymphoma and liver cancer. Selection bias differed for the studied outcomes, and a time window of a minimum of 2 months and 12 months, respectively, was judged to be appropriate. The novel method may have advantages compared with an interval-based method, especially in cohort studies with small numbers of events.
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