Importance of case age in the purported association between phylogenetics and hemolytic uremic syndrome inEscherichia coliO157:H7 infections

Abstract

AbstractEscherichia coliO157:H7 is the largest cause of hemolytic uremic syndrome (HUS). Previous studies proposed that HUS risk varies across theE. coliO157:H7 phylogenetic tree (hypervirulent clade 8), but the role of age in the association is unknown. We determined phylogenetic lineage ofE. coliO157:H7 isolates from 1160 culture-confirmedE. coliO157:H7 cases reported in Washington State, 2004–2015. Using generalised estimating equations, we tested the association between phylogenetic lineage and HUS. Age was evaluated as an effect modifier. Among 1082E. coliO157:H7 cases with both phylogenetic lineage and HUS status (HUSn= 76), stratified analysis suggested effect modification by age. Lineages IIa and IIb, relative to Ib, did not appear associated with HUS in children 0–9-years-old. For cases 10–59-years-old, lineages IIa and IIb appeared to confer increased risk of HUS, relative to lineage Ib. The association reversed in ⩾60-year-olds. Results were similar for clade 8. Phylogenetic lineage appears to be associated with HUS risk only among those ⩾10-years-old. Among children <10, the age group most frequently affected, lineage does not explain progression to HUS. However, lineage frequency varied across age groups, suggesting differences in exposure and/or early disease manifestation.