Identifying Human Encounters that Shape the Transmission ofStreptococcus Pneumoniaeand Other Respiratory Infections
Authors: de Waroux Olivier le Polain , Flasche Stefan , Kucharski Adam J , Langendorf Celine , Ndazima Donny , Mwanga-Amumpaire Juliet , Grais Rebecca F , Cohuet Sandra , Edmunds W John 
Published: March 2017

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 ofclose(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 ofcasualcontacts (<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 ofcloseinterpersonal contact is important for transmission of respiratory infections, but not that ofcasualcontacts. 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 summary

Although 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) ofStreptococcus pneumoniaeand 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 ofclosecontacts is important for transmission of respiratory infections, particularly pneumococcal carriage. In contrast, our study showed no association with the frequency of shortcasualcontacts. Those results are essential for both improving disease prevention and control efforts as well as informing research on infectious disease dynamics and transmission models.