Use of synthetic absorptive matrices to investigate pneumococcal carriage in children

Abstract

Pneumococcal infections have a devastating impact worldwide with upper respiratory tract carriage the pre-requisite for disease and transmission. The most common sampling method, nasopharyngeal swabbing, is uncomfortable and not optimal for use in children. We

therefore tested a novel technique with a synthetic absorptive matrix and applied it in two separate clinical studies to investigate nasal pneumococcal carriage and host-pathogen interactions.

In the FAMILY Micro study, 40 healthy families in England collected saliva and nasal fluid at home every two weeks for six months, completed questionnaires and were invited for an interview. In the ENRICH study, nasopharyngeal swabs and nasal fluid were collected from Kenyan children: infants in the control (n=27) and probiotic intervention arms (n=30) of the PROSYNK study and their contacts under five (n=56). In both studies, respiratory pathogens were detected by species-specific qPCR. Cytokine levels in nasal fluid were measured by Luminex, transition metal concentrations by ICP-MS and Leptin by ELISA.

Compliance with and acceptability of sampling in UK families were generally high, but lowest in young children. While older children experienced little pain (0.3%) or discomfort (7%), sampling in children under five was more painful (14%) and uncomfortable (33%). Young

children hated anything inserted in their nose, but older children preferred minimally invasive sampling over nasopharyngeal swabs.

Pneumococcal carriage and density varied between families and individuals in the UK, remaining high overall despite COVID-19 restrictions.

In Kenyan children, pneumococcal carriage rates (p=0.16) and densities (p=0.02) were lower in those who had received probiotic intervention from birth. These children also had higher nasal concentrations of IL-13 (p=0.012), IL-12/IL-23 (p=0.021), MCP-1 (p=0.017), eotaxin (0.0064), IL-2R (p=0.044) and IL-7 (p=0.025).

With respect to the effect of nutritional status on the nasal microenvironment, lower height for-age was associated with low calcium concentrations (p=0.048) and higher RANTES concentrations (p=0.016) in Kenyan children, while lower weight-for-height was related to higher concentrations of IL-10 (p=0.0026), eotaxin (p=0.0025), IL-17A (p=0.0011), MCP-1 (p=0.0078), HGF (p=0.0081) and VEGF-A (p=0.0016). Leptin was only detected in 5% of Kenyan samples but in UK samples, leptin concentrations were higher in overweight than healthy children (p=0.25). There were no differences in pneumococcal carriage rates or densities according to nutritional status in either study.

Synthetic absorptive matrices can be used to study pneumococcal carriage. Potential effects of probiotic intervention and nutritional status on the nasal niche and carriage dynamics should be corroborated in larger studies