sexual networks in contemporary western societies fredrik liljeros karolinska institutet stockholm...
TRANSCRIPT
Sexual Networks in Contemporary Western
Societies
Fredrik Liljeros
Karolinska institutet
Stockholm University
(Supported by the Swedish Institute for Public Health)
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How is it possible for Sexually transmitted Infections (STI’s) to reproduce themselves when the average reported life number of contacts are as low as 6-12 in western societies?
Why do we have STI’s at all?
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Data sources
National surveys
+ Representative
-Validity?
-Low Response rate
-Only ego network data
Clinical data
+ Network data
-Validity?
-Representative?
Local networks
+ Network data
-Validity?
Representative?
Online networks
+ Network data
-Validity?
Representative
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Representative
Sample Population
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Network data vs ego network data
MaleFemale
?
?
??
?
?
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Validity
Women report twice as few partners on average than men do
Find at least five explanations!
Low response rate
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Data sources
National surveys
+ Representative
-Validity?
-Low Response rate
-Only ego network data
Clinical data
+ Network data
-Validity?
-Representative?
Local networks
+ Network data
-Validity?
Representative?
Online networks
+ Network data
-Validity?
Representative
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Triangulation
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Basic epidemiology
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Reproduction Rate, R
Average number of contacts * probability for transmission * duration of infectiousness
Low for STIs !
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Basic Reproduction Rate, R0
Gottland
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Reported HIV infected in Sweden
www.smittskyddsinstitutet.se S-GEM
Reported Chlamydia infected in Sweden
www.smittskyddsinstitutet.se
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Explanations for the current situation
Probably no single explanation!
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On average, your partners have more partners than you !
8.19
818
k
5.416
8818
partnersk
Newman Social Networks (2003)
May and Anderson Nature (1987)
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The Core-Group Theory
”Scale free distribution of partners ”
Liljeros et al Nature (2001)
National survey data S-GEM
Gay men attending a STI clinic in London
Colgate et al PNAS (1989)S-GEM
Internet contact site data
Holme, Edling and Liljeros Social networks 2004
Prefferential attachent?
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Concurrency A B
C
D E
AC AB
DC DE
2b.
Contact
network
Line graph
Morris and Kretzchmar Social Networks (1995) S-GEM
Concurrency
A B
C
D E
Contact
network
Line graph
Kretzchmar and Morris Social Networks (1995)
?
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Concurrency A B
C
D E
A B
C
D E
AC BC
DC EC
2a.
AC AB
DC DE
2b.
Contact
network
Line graph
Kretzchmar and Morris Social Networks (1995) S-GEM
Assortative interaction
Newman PRL 2002Liljeros Edling and Amaral (2003)
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Bearman, Moodey and Stovel Forthcoming in AJS(With permission from P. Bearman)
Local network motifs
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Australia
Thailand
USA
Holland
Norway
Spain
England
Greece
Switzerland
231 cases
ÖrebroAustria
Falk et al STI (2003)
Örebro hospital: Local of infection with Chlamydia
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Conclusions
• Standard deviation is of high importance
• Contact tracing are likely to be effective
• Targeted interventions
Further reading….
Liljeros F, Edling CR, Amaral LAN ”Sexual networks: implications for the transmission of sexually transmitted infections”
MICROBES INFECT 5 (2): 189-196 FEB 2003 S-GEM
Take home message
Your partners have more partners than you have yourself!
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