Identifying transmission routes of Streptococcus pneumoniae and sources of acquisitions in high transmission communities

Abstract

Identifying the transmission sources and reservoirs of Streptococcus pneumoniae (SP) is a long-standing question for pneumococcal epidemiology, transmission dynamics, and vaccine policy. Here we use serotype to identify SP transmission and examine acquisitions (in the same household, local community, and county, or of unidentified origin) in a longitudinal cohort of children and adults from the Navajo Nation and the White Mountain Apache American Indian Tribes. We found that adults acquire SP relatively more in the household than other age groups, and children 2-8 years old typically acquire in their own or surrounding communities. Age-specific transmission probability matrices show that transmissions within household were mostly seen from older to younger siblings. Outside the household, children most often transmit to other children in the same age group, showing age-assortative mixing behavior. We find toddlers and older children to be most involved in SP transmission and acquisition, indicating their role as key drivers of SP epidemiology. Although infants have high carriage prevalence, they do not play a central role in transmission of SP compared with toddlers and older children. Our results are relevant to inform alternative pneumococcal conjugate vaccine dosing strategies and analytic efforts to inform optimization of vaccine programs, as well as assessing the transmission dynamics of pathogens transmitted by close contact in general.

Keywords: Streptococcus pneumoniae (pneumococcus); Infectious disease epidemiology; modelling; spread of disease; vaccine policy development.

Fig. 1.

Percentage of subjects with positive NP carriage of SP by age in all seven visits, with 95% confidence intervals.

Fig. 2.

Acquisition sources by age group. Figure shows the percentage of SP acquired within an individual's household, their community, their service unit (SU), another SU, or with no discernible source. Binomial confidence intervals are plotted as whiskers.

Fig. 3.

Number of contacts across age groups. Figure shows the number of potential contacts between age groups within the household, community, and service unit.

Fig. 4.

Proportion of contacts that result in SP transmission between ages. Figure shows the transmission probabilities of SP by age groups from individuals on the Y-axis to individuals on the X-axis within the household, community, or service unit (multiple communities). Transmission probabilities are calculated as the proportion of potential contacts in an age pair (i.e. 3–4 to 2–3 year olds) that resulted in transmission. Transmission events that were not statistically significant are plotted in small italics.