Networks and the epidemiology of directly transmitted infectious diseases are fundamentally linked. The foundations of epidemiology and early epidemiological models were based on population wide random-mixing, but in practice each individual has a finite set of contacts to whom they can pass infection; the ensemble of all such contacts forms a ‘mixing network’. Knowledge of the structure of the network allows models to compute the epidemic dynamics at the population scale from the individual-level behaviour of infections. Therefore, characteristics of mixing networks—and how these deviate from the random-mixing norm—have become important applied concerns that may enhance the understanding and prediction of epidemic patterns and intervention measures. Here, we review the basis of epidemiological theory (based on random-mixing models) and network theory (based on work from the social sciences and graph theory). We then describe a variety of methods that allow the mixing network, or an approximation to the network, to be ascertained. It is often the case that time and resources limit our ability to accurately find all connections within a network, and hence a generic understanding of the relationship between network structure and disease dynamics is needed. Therefore, we review some of the variety of idealized network types and approximation techniques that have been utilized to elucidate this link. Finally, we look to the future to suggest how the two fields of network theory and epidemiological modelling can deliver an improved understanding of disease dynamics and better public health through effective disease control.

/pdf/networks-and-epidemic-models-1qt352hzh3.pdf

Networks and epidemic models.

https://kops.uni-konstanz.de/bitstream/handle/123456789/5940/variants.pdf;sequence=1

On variants of shortest-path betweenness centrality and their generic computation ☆

Network analysis is an approach to research that is uniquely suited to describing, exploring, and understanding structural and relational aspects of health. It is both a methodological tool and a theoretical paradigm that allows us to pose and answer important ecological questions in public health. In this review we trace the history of network analysis, provide a methodological overview of network techniques, and discuss where and how network analysis has been used in public health. We show how network analysis has its roots in mathematics, statistics, sociology, anthropology, psychology, biology, physics, and computer science. In public health, network analysis has been used to study primarily disease transmission, especially for HIV/AIDS and other sexually transmitted diseases; information transmission, particularly for diffusion of innovations; the role of social support and social capital; the influence of personal and social networks on health behavior; and the interorganizational structure of health systems. We conclude with future directions for network analysis in public health.

https://www.annualreviews.org/doi/pdf/10.1146/annurev.publhealth.28.021406.144132

Network Analysis in Public Health: History, Methods, and Applications

Background 
The structure of sexual contact networks plays a key role in the epidemiology of sexually transmitted infections, and their reconstruction from interview data has provided valuable insights into the spread of infection. For HIV, the long period of infectivity has made the interpretation of contact networks more difficult, and major discrepancies have been observed between the contact network and the transmission network revealed by viral phylogenetics. The high rate of HIV evolution in principle allows for detailed reconstruction of links between virus from different individuals, but often sampling has been too sparse to describe the structure of the transmission network. The aim of this study was to analyze a high-density sample of an HIV-infected population using recently developed techniques in phylogenetics to infer the short-term dynamics of the epidemic among men who have sex with men (MSM).
Methods and Findings 
Sequences of the protease and reverse transcriptase coding regions from 2,126 patients, predominantly MSM, from London were compared: 402 of these showed a close match to at least one other subtype B sequence. Nine large clusters were identified on the basis of genetic distance; all were confirmed by Bayesian Monte Carlo Markov chain (MCMC) phylogenetic analysis. Overall, 25% of individuals with a close match with one sequence are linked to 10 or more others. Dated phylogenies of the clusters using a relaxed clock indicated that 65% of the transmissions within clusters took place between 1995 and 2000, and 25% occurred within 6 mo after infection. The likelihood that not all members of the clusters have been identified renders the latter observation conservative.
Conclusions 
Reconstruction of the HIV transmission network using a dated phylogeny approach has revealed the HIV epidemic among MSM in London to have been episodic, with evidence of multiple clusters of transmissions dating to the late 1990s, a period when HIV prevalence is known to have doubled in this population. The quantitative description of the transmission dynamics among MSM will be important for parameterization of epidemiological models and in designing intervention strategies.

/pdf/episodic-sexual-transmission-of-hiv-revealed-by-molecular-rstiutgfri.pdf

Episodic Sexual Transmission of HIV Revealed by Molecular Phylodynamics

First responders, including military health care workers, public health service workers, and state, local, and volunteer first responders serve an important role in protecting our nation's citizenry in the aftermath of disaster. Protecting our nation's health is a vital part of preserving national security and the continuity of critical national functions. However, public health and public safety workers experience a broad range of health and mental health consequences as a result of work-related exposures to natural or man-made disasters. This chapter reviews recent epidemiologic studies that broaden our understanding of the range of health and mental health consequences for first responders. Evidence-based psychopharmacologic and psychotherapeutic interventions for posttraumatic distress reactions and psychiatric disorders are outlined. Finally, the application of public health intervention models for the assessment and management of distress responses and mental disorders in first-responder communities is discussed.

First Responders: Mental Health Consequences of Natural and Human-Made Disasters for Public Health and Public Safety Workers*

Objectives: Sexual partnerships can be viewed as networks in order to study disease transmission. We examined the transmission of Neisseria gonorrhoeae in a localised outbreak in Alberta, Canada, using measures of network centrality to determine the association between risk of infection of network members and their position within the sexual network. We also compared risk in smaller disconnected components with a large network centred on a social venue. Methods: During the investigation of the outbreak, epidemiological data were collected on gonorrhoea cases and their sexual contacts from STI surveillance records. In addition to traditional contact tracing information, subjects were interviewed about social venues they attended in the past year where casual sexual partnering may have occurred. Sexual networks were constructed by linking together named partners. Univariate comparisons of individual network member characteristics and algebraic measures of network centrality were completed. Results: The sexual networks consisted of 182 individuals, of whom 107 were index cases with laboratory confirmed gonorrhoea and 75 partners of index cases. People who had significantly higher information centrality within each of their local networks were found to have patronised a popular motel bar in the main town in the region (p = 0.05). When the social interaction through the bar was considered, a large network of 89 individuals was constructed that joined all eight of the largest local networks. Moreover, several networks from different communities were linked by individuals who served as bridge populations as a result of their sexual partnering. Conclusion: Asking clients about particular social venues emphasised the importance of location in disease transmission. Network measures of centrality, particularly information centrality, allowed the identification of key individuals through whom infection could be channelled into local networks. Such individuals would be ideal targets for increased interventions.

https://sti.bmj.com/content/sextrans/80/4/280.full.pdf

Sexual network analysis of a gonorrhoea outbreak

Background
The Public Health Agency of Canada's integrated bio-behavioural surveillance system-Tracks surveys-assesses the burden of HIV, hepatitis C and associated risks in key populations in Canada. From 2018-2020, Tracks surveys were successfully implemented by First Nations Health Services Organizations in Alberta and Saskatchewan.


Methods
First Nations-led survey teams invited community members who identified as First Nations, Inuit or Métis to participate in Tracks surveys and testing for HIV, hepatitis C and syphilis. Information was collected on social determinants of health, use of prevention services, substance use, sexual behaviours and care for HIV and hepatitis C. Descriptive statistics are presented.


Results
Of the 1,828 survey participants, 97.4% self-identified as First Nations and 91.4% lived in an on-reserve community. Over half (52.2%) were cisgender female, average age was 36.3 years, 82.5% lived in stable housing, 82% had access to primary healthcare and 73.8% reported having good to excellent mental health. Most participants (97%) had a family member who had experienced residential school. High proportions experienced stigma and discrimination (65.6%), financial strain (64.3%) and abuse in childhood (65.1%). Testing for HIV (62.8%) and hepatitis C (55.3%) was relatively high. Prevalence of HIV was 1.6% (of whom 64% knew their infection status). Hepatitis C ribonucleic acid prevalence was 5% (44.9% of whom knew their current infection status).


Conclusion
Historical and ongoing experiences of trauma, and higher prevalence of hepatitis C were identified, reaffirming evidence of the ongoing legacies of colonialism, Indian Residential Schools and systemic racism. High participation in sexually transmitted blood-borne infection testing and prevention reflect the importance of First Nations-led culturally sensitive, safe and responsive healthcare services and programs to effect improved outcomes for First Nations peoples.

/pdf/summary-findings-from-tracks-surveys-implemented-by-first-2nbxl83u.pdf

W Yacoub

Papers

Sexual network analysis of a gonorrhoea outbreak

Summary findings from Tracks surveys implemented by First Nations in Saskatchewan and Alberta, Canada, 2018-2020.