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International Biometric Society
INVESTIGATING SOCIAL CONTACT STRUCTURES AND THEIR INTERACTIONS WITH DIFFERENT TYPES
OF TIME USE IN SUB-SAHARAN AFRICA
Alessia Melegaro1, Emanuele Del Fava1, Piero Poletti1,2, Constance Nyamukapa3, and
Simon Gregson3
1
Bocconi University, Milan, Italy
Fondazione Bruno Kessler, Trento, Italy
3
Imperial College London, UK
2
In the field of modelling infectious diseases, epidemiological literature has shown the
importance of considering social contact structures when investigating the routes of
transmission of airborne infections diseases and the subsequent effect of control measures
put in act in order to stop transmission. Traditional transmission models assume that people
mix with each other in a homogenous way. However, this assumption is far from being
realistic. In the past, research has tried to solve this problem by hypothesizing theoretical
social structures, most of which assumed high assortativeness between people belonging to
the same age group and more or less homogeneity for contacts between people belonging
to different age groups (Anderson and May, 1991). However, in recent years research has
moved forward from this approach by directly collecting field data on social contacts among
people, including both physical and conversational contacts. Seminal studies in Europe
showed that, along with a strong assortativeness in contacts between people of the same
age group, to a greater extent among school-aged children, a great number of contacts is
registered between adults and children. Stratifying contacts per location (household, school,
workplace, and general community), it has been seen that those high-frequency contacts
occurred mostly in household, usually between parents and their children. The school is
another location characterized by a high frequency of contacts. In order to validate these
contact data, their inclusion in models for transmission of childhood infections has lead to a
far better explanation of the available infection data (seroprevalence and incidence data).
However, many questions still remain open. One of these regards the investigation of the
impact of social contact structures in contexts characterised by an ongoing demographic
transition, as it is the case of Sub-Saharan Africa and other middle/low income countries. In
countries that show at the same time large households, composed of people belonging to
different generations, mostly in rural areas, and smaller households in the fast-growing
urban areas, can we expect a different stratification of social contact structures between
different age groups and locations? Moreover, how do social contact structures differ among
people with very different use of their time during the day? We expect indeed different
patterns between someone who spends most of his/her day at home and someone who
spends his/her day either at school or on the workplace.
We try to answer all these questions by collecting, for the first time to our knowledge, field
data on social contacts and on time use from Zimbabwe, a Sub-Saharan African country still
prevalently rural, where HIV has reached an endemic state. Our sample consists of around
1200 subjects mainly living in two different areas, one mostly rural and one mostly urban.
People included in the study were asked to keep a diary for two continuous days, randomly
allocated, in order to collect information on their social contacts and on their time use. As
regards contacts, they were asked to give information on age, gender, relationship, type
(physical/non-physical), and location for each of their contacts; as regards time use, they
were asked to record their location (household, school, workplace, general community) in
different time slots during the day and also to give a rough estimate of the number of people
around them.
The combination of these two sources of data will allow us to better characterise the shape
of social contact patterns for different types of time use and to subsequently inform a
mathematical model designed to assess the impact of different policy measures on the
control of the transmission of infectious diseases of high concern in the country.
International Biometric Conference, Florence, ITALY, 6 – 11 July 2014