| 1. |
- Bengtsson, Linus, et al.
(författare)
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Implementation of Web-Based Respondent-Driven Sampling among Men Who Have Sex with Men in Vietnam
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:11, s. e49417-
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Lack of representative data about hidden groups, like men who have sex with men (MSM), hinders an evidence-based response to the HIV epidemics. Respondent-driven sampling (RDS) was developed to overcome sampling challenges in studies of populations like MSM for which sampling frames are absent. Internet-based RDS (webRDS) can potentially circumvent limitations of the original RDS method. We aimed to implement and evaluate webRDS among a hidden population. Methods and Design: criteria were men, aged 18 and above, who had ever had sex with another man and were living in Vietnam. Participants were invited by an MSM friend, logged in, and answered a survey. Participants could recruit up to four MSM friends. We evaluated the system by its success in generating sustained recruitment and the degree to which the sample compositions stabilized with increasing sample size. Results: Twenty starting participants generated 676 participants over 24 recruitment waves. Analyses did not show evidence of bias due to ineligible participation. Estimated mean age was 22 years and 82% came from the two large metropolitan areas. 32 out of 63 provinces were represented. The median number of sexual partners during the last six months was two. The sample composition stabilized well for 16 out of 17 variables. Conclusion: Results indicate that webRDS could be implemented at a low cost among Internet-using MSM in Vietnam. WebRDS may be a promising method for sampling of Internet-using MSM and other hidden groups.
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| 2. |
- Brouwers, Lisa, 1967-, et al.
(författare)
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Economic consequences to society of pandemic H1N1 influenza 2009 : preliminary results for Sweden
- 2009
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Ingår i: Eurosurveillance. - : European Centre for Disease Control and Prevention (ECDC). - 1025-496X .- 1560-7917. ; 14:37, s. 19333-
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Tidskriftsartikel (refereegranskat)abstract
- Experiments using a microsimulation platform show that vaccination against pandemic H1N1 influenza is highly cost-effective. Swedish society may reduce the costs of pandemic by about SEK 2.5 billion (approximately EUR 250 million) if at least 60 per cent of the population is vaccinated, even if costs related to death cases are excluded. The cost reduction primarily results from reduced absenteeism. These results are preliminary and based on comprehensive assumptions about the infectiousness and morbidity of the pandemic, which are uncertain in the current situation.
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| 3. |
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| 4. |
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| 5. |
- Camitz, Martin
(författare)
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Computer aided infectious disease epidemiology : bridging to public health
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores the junctions of mathematical and computer modeling of infectious disease epidemics, the basis of such research and the communication of results. With increasing frequency we turn to computers and software for any type of research problem encountered. Computer modeling is a blessing with many hidden trapdoors. Skipping mathematical modeling, resorting to code immediately, is ill advised. Validity, uncertainty, bugs and old mathematical truths must all be taken under careful consideration. The same duality is present in the communication of the results from computer models to the public, to decision makers and to peers. These topics are discussed in the context of four contributing papers. The first paper describes a computer model of an infectious disease epidemic in Sweden. Using Swedish travel data we were able to demonstrate a way of successfully restricting travel to delay the spread of disease. The second paper discusses a known fallacy common to many epidemic models, often overlooked when mathematical models are simulated on computers. It is demonstrated that it must be considered also with more complex models. The model in Paper I is used to exemplify the problem. The third study takes the parsimonial considerations of the first two papers to another level, proposing static models for use in epidemic modeling. Understanding, an eluding - especially in computer models - but essential component in all models, is benefited. The fourth study explores the epidemiology of sexual networks. Using survey datasets we show that with high probability, the sexually active population is largely connected, in a so called giant component, rendering the Swedish population an ideal isotope for sexually transmitted pathogens.
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| 6. |
- 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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| 7. |
- Camitz, Martin, et al.
(författare)
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The effect of travel restrictions on the spread of a moderately contagious disease
- 2006
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Ingår i: BMC Medicine. - : Springer Science and Business Media LLC. - 1741-7015. ; 4, s. 32-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Much research in epidemiology has been focused on evaluating conventional methods of control strategies in the event of an epidemic or pandemic. Travel restrictions are often suggested as an efficient way to reduce the spread of a contagious disease that threatens public health, but few papers have studied in depth the effects of travel restrictions. In this study, we investigated what effect different levels of travel restrictions might have on the speed and geographical spread of an outbreak of a disease similar to severe acute respiratory syndrome (SARS). Methods: We used a stochastic simulation model incorporating survey data of travel patterns between municipalities in Sweden collected over 3 years. We tested scenarios of travel restrictions in which travel over distances > 50 km and 20 km would be banned, taking into account different levels of compliance. Results: We found that a ban on journeys > 50 km would drastically reduce the speed and geographical spread of outbreaks, even when compliance is < 100%. The result was found to be robust for different rates of intermunicipality transmission intensities. Conclusion: This study supports travel restrictions as an effective way to mitigate the effect of a future disease outbreak.
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| 8. |
- Camitz, Martin, et al.
(författare)
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Travel restrictions for moderately contagious diseases
- 2011. - 1
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Ingår i: Hospitality and Health: Issues and Developments. - : Apple Academic Press. - 9781466560000 - 9781926692920 ; , s. 95-105
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Much research in epidemiology has been focused on evaluating conventional methods of control strategies in the event of an epidemic or pandemic. Travel restrictions are often suggested as an efficient way to reduce the spread of a contagious disease that threatens public health, but few chapters have studied in depth the effects of travel restrictions. In this study, we investigated what effect different levels of travel restrictions might have on the speed and geographical spread of an outbreak of a disease similar to severe acute respiratory syndrome (SARS).
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| 9. |
- Lu, Xin, et al.
(författare)
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Finding the shortest paths by node combination
- 2011
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Ingår i: Applied Mathematics and Computation. - : Elsevier BV. - 0096-3003 .- 1873-5649. ; 217:13, s. 6401-6408
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Tidskriftsartikel (refereegranskat)abstract
- By repeatedly combining the source node's nearest neighbor, we propose a node combination (NC) method to implement the Dijkstra's algorithm. The NC algorithm finds the shortest paths with three simple iterative steps: find the nearest neighbor of the source node, combine that node with the source node, and modify the weights on edges that connect to the nearest neighbor. The NC algorithm is more comprehensible and convenient for programming as there is no need to maintain a set with the nodes' distances. Experimental evaluations on various networks reveal that the NC algorithm is as efficient as Dijkstra's algorithm. As the whole process of the NC algorithm can be implemented with vectors, we also show how to find the shortest paths on a weight matrix.
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| 10. |
- Lu, Xin, et al.
(författare)
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The sensitivity of respondent-driven sampling
- 2012
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Ingår i: Journal of the Royal Statistical Society. - 0964-1998 .- 1467-985X. ; 175:1, s. 191-216
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Tidskriftsartikel (refereegranskat)abstract
- Researchers in many scientific fields make inferences from individuals to larger groups. For many groups, however, there is no list of members from which to draw a random sample. Respondent-driven sampling (RDS) is a relatively new sampling methodology that circumvents this difficulty by using the social networks of the groups under study. The RDS method has been shown to provide unbiased estimates of population proportions given certain conditions. The method is now widely used in human immunodeficiency virus related studies among high risk populations globally. We test the RDS methodology by simulating RDS studies on the social networks of a large Lesbian, gay, bisexual and transgender Web community. The robustness of the RDS method is tested by violating, one by one, the conditions under which the method provides unbiased estimates. Simulations indicate that the bias is large if networks are directed or respondents choose to invite people on the basis of characteristics that are correlated with the study outcomes. The bias and variance increase if participants invite close as opposed to more distant friends whereas sampling in denser networks sharply reduces variance. However, the RDS method shows strong resistance to sampling without replacement, low response rates and certain errors in the participants reporting of their network sizes, as well as the selection criteria of seeds. The effects of network structure and the number of seeds and coupons are also discussed.
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