Close encounters between infants and household members measured through wearable proximity sensors

Abstract

Describing and understanding close proximity interactions between infant and family members can provide key information on transmission opportunities of respiratory infections within households. Among respiratory infections, pertussis represents a public health priority. Pertussis infection can be particularly harmful to young, unvaccinated infants and for these patients, family members represent the main sources of transmission. Here, we report on the use of wearable proximity sensors based on RFID technology to measure face-to-face proximity between family members within 16 households with infants younger than 6 months for 2-5 consecutive days of data collection. The sensors were deployed over the course of approximately 1 year, in the context of a national research project aimed at the improvement of infant pertussis prevention strategies. We investigated differences in close-range interactions between family members and we assessed whether demographic variables or feeding practices affect contact patterns between parents and infants. A total of 5,958 contact events were recorded between 55 individuals: 16 infants, 4 siblings, 31 parents and 4 grandparents. The aggregated contact networks, obtained for each household, showed a heterogeneous distribution of the cumulative time spent in proximity with the infant by family members. Contact matrices defined by age and by family role showed that most of the contacts occurred between the infant and other family members (70%), while 30% of contacts was among family members (infants excluded). Many contacts were observed between infants and adults, in particular between infant and mother, followed by father, siblings and grandparents. A larger number of contacts and longer contact durations between infant and other family members were observed in families adopting exclusive breastfeeding, compared to families in which the infant receives artificial or mixed feeding. Our results demonstrate how a high-resolution measurement of contact matrices within infants' households is feasible using wearable proximity sensing devices. Moreover, our findings suggest the mother is responsible for the large majority of the infant's contact pattern, thus being the main potential source of infection for a transmissible disease. As the contribution to the infants' contact pattern by other family members is very variable, vaccination against pertussis during pregnancy is probably the best strategy to protect young, unvaccinated infants.

Fig 1. Distribution of contact durations.

Probability density distribution P(dt) of contact duration dt in seconds, measured for all individuals over the whole experimental period.

Fig 2. Contact matrices of the mean contact durations per capita (left panel) and the mean contact events per capita (right panel) by age categories for all individuals.

Fig 3. Contact matrices of the mean contact durations per capita (left panel) and the mean contact events per capita (right panel) by roles for all individuals.

Fig 4. Contact networks between household members aggregated over the whole study duration.

Nodes are color-coded according to the role of the family member. Edge thickness is proportional to the total time spent in proximity by two connected individuals, and the edge gradient colour indicates the intensity of the contact between household members (blue = less contacts; red = more contacts).

Fig 5. Distribution of cosine similarity measured for each node of the full contact network (overall) and for each single household.

Distributions are obtained by measuring the cosine similarity of each node's neighbourhood, for each pair of days of data collection. The box and whisker plots show the interquartile range, and the red line indicates the median value. The error bars extend from the box to the highest and lowest values. The households are ordered from left to right by increasing number of edges in the contact network.

Fig 6. Infant proximity score (IPS) between each family members and the infant (IPS = percentage of time spent by each family member in proximity to the infant, over the total time spent by the infant at home).

Pink = IPS between mother and infant; blue = IPS between father and infant, green = IPS between sibling and infant; yellow = IPS between grandparent and infant. Families in which the infant is exclusively breastfed are labelled with *.