Biomedical subjects

Fredrik Liljeros

Publications and source records attributed to Fredrik Liljeros.

5 recordsLinked to original sources

PubMed2007

Spatial bridges and the spread of Chlamydia: the case of a county in Sweden.

OBJECTIVES: The so-called small-world effect can have a great impact on efforts to control the incidence and prevalence of sexually transmitted infections. This is because a small number of so-called spatial bridgers (individuals who, through sexual contacts, interconnect geographically distant areas) can drastically lower the average path length in the sexual network and, as a result, make locally based intervention programs much less effective. The objectives of this study were to analyze the sociodemographic characteristics of these bridgers and to compare the result with the remaining study population. The purpose was to determine whether it is possible to identify them for targeted intervention programs. STUDY DESIGN: During 2001, contact tracing was performed in approximately 98% of all cases with positive test results in Värmland County. The sexual networks obtained constituted a study population of 851 individuals. Statistical analysis was used to characterize individuals engaged in spatial bridging behavior. RESULTS: Approximately 8% of the study population was characterized as spatial bridgers. Using multivariate analysis, we found almost no significant differences between these individuals and the rest of the study population when it came to sociodemographic variables, including education, economy, and ethnicity. CONCLUSION: The number of spatial bridgers is high enough to create a small-world network with links that can fuel the endemic chlamydia in Värmland County. Sociodemographic information could not be used to characterize spatial bridgers. In interventions against chlamydia, spatial bridgers shall be considered as potentially important for sustaining the disease.

Adolescent↗

PubMed2006

The effect of travel restrictions on the spread of a moderately contagious disease.

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.

Communicable Diseases↗

PubMed2006

Number of sexual encounters involving intercourse and the transmission of sexually transmitted infections.

OBJECTIVE: To investigate the impact of the number of sexual encounters involving intercourse in combination with the number of sexual partners on the transmission dynamics of sexually transmitted infections (STIs). STUDY: A statistical model is used for predicting the basic reproductive rate, R(0), which takes both the number of sexual partners and the number of sexual encounters involving intercourse per partner into consideration. The model is then applied to Swedish survey data that includes data on the number of partners over the course of 1 year, as well as the number of encounters per partner during this time. RESULTS: The number of sexual encounters involving intercourse in combination with the number of sexual partners affects the number of secondary infections in a nonlinear way. The basic reproductive rate, R(0), is lower when the heterogeneity in number of encounters is modeled than when homogeneity is assumed. CONCLUSION: The results indicate that it is possible that individuals who have a large number of partners may not, as is often assumed, be the only ones to play a central role as spreaders of STIs. Individuals who have a large number of sexual encounters involving intercourse per partner and have several (but not necessarily a very large number of) partners may also play a significant role in the transmission of STIs.

Contact Tracing↗

PubMed2003

Network bipartivity.

Systems with two types of agents with a preference for heterophilous interaction produce networks that are more or less close to bipartite. We propose two measures quantifying the notion of bipartivity. The two measures-one well known and natural, but computationally intractable, and the other computationally less complex, but also less intuitive-are examined on model networks that continuously interpolate between bipartite graphs and graphs with many odd circuits. We find that the bipartivity measures increase as we tune the control parameters of the test networks to intuitively increase the bipartivity, and thus conclude that the measures are quite relevant. We also measure and discuss the values of our bipartivity measures for empirical social networks (constructed from professional collaborations, Internet communities, and field surveys). Here we find, as expected, that networks arising from romantic online interaction have high, and professional collaboration networks have low, bipartivity values. In some other cases, probably due to low average degree of the network, the bipartivity measures cannot distinguish between romantic and friendship oriented interaction.

Journal Article↗

PubMed2003

Sexual networks: implications for the transmission of sexually transmitted infections.

The structures of sexual networks are essential for understanding the dynamics of sexually transmitted infections. Standard epidemiological models largely disregard the complex patterns of intimate contacts. Social network analysis offers important insight into how to conceptualize and model social interaction and has the potential to greatly enhance the understanding of disease epidemics.

Contact Tracing↗