BackgroundQuantification of human interactions relevant to infectious disease transmission through social contact is central to predict disease dynamics, yet data from low-resource settings remain scarce.MethodsWe undertook a social contact survey in rural Uganda, whereby participants were asked to recall details about the frequency, type, and socio-demographic characteristics of any conversational encounter that lasted for ≥5 min (henceforth defined as ‘contacts’) during the previous day. An estimate of the number of ‘casual contacts’ (i.e. < 5 min) was also obtained.ResultsIn total, 566 individuals were included in the study. On average participants reported having routine contact with 7.2 individuals (range 1-25). Children aged 5-14 years had the highest frequency of contacts and the elderly (≥65 years) the fewest (P < 0.001). A strong age-assortative pattern was seen, particularly outside the household and increasingly so for contacts occurring further away from home. Adults aged 25-64 years tended to travel more often and further than others, and males travelled more frequently than females.ConclusionOur study provides detailed information on contact patterns and their spatial characteristics in an African setting. It therefore fills an important knowledge gap that will help more accurately predict transmission dynamics and the impact of control strategies in such areas.Electronic supplementary materialThe online version of this article (10.1186/s12879-018-3073-1) contains supplementary material, which is available to authorized users.

HighlightsIndividual risk of pneumococcal carriage and of acute respiratory symptoms increases with the number of close contacts.More frequent contact with young children increases the risk of pneumococcal carriage in adults.The risk of nasopharyngeal carriage did not increase with the frequency of short casual contacts, irrespective of age.

In Sheema district, the proportion of PCV10 serotypes was low (<40%), across all age groups, especially among individuals aged 15years or older (<5%). PCV10 introduction is likely to impact transmission among children and to older individuals, but less likely to substantially modify pneumococcal NP ecology among individuals aged 15years or older.

ABSTRACT

Although patterns of social contacts are believed to be an important determinant of infectious disease transmission, there is little empirical evidence to back this up. Indeed, no previous study has linked individuals’ risk of respiratory infection with their current pattern of social contacts. We explored whether the frequency of different types of social encounters were associated with current pneumococcal carriage and self-reported acute respiratory symptoms (ARS), though a survey in Uganda in 2014. In total 566 participants were asked about their daily social encounters and about symptoms of ARS in the last two weeks. A nasopharyngeal specimen was also taken from each participant. We found that the frequency of physical (i.e. skin-to-skin), long (≥1h) and household contacts – which capture some measure of close (i.e. relatively intimate) contact –, was higher among pneumococcal carriers than non-carriers, and among people with ARS compared to those without, irrespective of their age. With each additional physical encounter the age-adjusted risk of carriage and ARS increased by 6% (95%CI 2-9%) and 9% (1-18%) respectively. In contrast, the number of casual contacts (<5 minutes long) was not associated with either pneumococcal carriage or ARS. A detailed analysis by age of contacts showed that the number of close contacts with young children (<5 years) was particularly higher among older children and adult carriers than non-carriers, while the higher number of contacts among people with ARS was more homogeneous across contacts of all ages. Our findings provide key evidence that the frequency of close interpersonal contact is important for transmission of respiratory infections, but not that of casual contacts. Such results strengthen the evidence for public health measures based upon assumptions of what contacts are important for transmission, and are important to improve disease prevention and control efforts, as well as inform research on infectious disease dynamics.Author summaryAlthough social contacts are an important determinant for the transmission of many infectious diseases it is not clear how the nature and frequency of contacts shape individual infection risk. We explored whether frequency, duration and type of social encounters were associated with someone’s risk of respiratory infection, using nasopharyngeal carriage (NP) of Streptococcus pneumoniae and acute respiratory symptoms as endpoints. To do so, we conducted a survey in South-West Uganda collecting information on people’s social encounters, respiratory symptoms, and pneumococcal carriage status. Our results show that both pneumococcal carriage and respiratory symptoms are independently associated with a higher number of social encounters, irrespective of a person’s age. More specifically, our findings strongly suggest that the frequency of close contacts is important for transmission of respiratory infections, particularly pneumococcal carriage. In contrast, our study showed no association with the frequency of short casual contacts. Those results are essential for both improving disease prevention and control efforts as well as informing research on infectious disease dynamics and transmission models.