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Escherichia coli O157:H7 is the largest cause of hemolytic uremic syndrome (HUS). Previous studies proposed that HUS risk varies across the E. coli O157:H7 phylogenetic tree (hypervirulent clade 8), but the role of age in the association is unknown. We determined phylogenetic lineage of E. coli O157:H7 isolates from 1160 culture-confirmed E. coli O157: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 1082 E. coli O157:H7 cases with both phylogenetic lineage and HUS status (HUS n = 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.
Ninety-two individuals of Sitobion avenae (F.) collected throughout Britain in 1979 and 1980, were cloned and investigated genetically by electrophoresis of 14 enzymes representing 26 loci. Percentage polymorphism (P) differed considerably between years, 64% (16/25 loci) in 1979 and 19% (5/26) in 1980, whereas average heterozygosity () was low (ca. 2%) in both years and confined mainly to one locus, EST-1. The prevalence of homozygous allozyme variation supports ecological findings suggesting S. avenae to be largely anholocyclic in Britain. In 1981 and 1982, large populations, sampled from 11 sites in Britain and Spain, were examined at 13 loci. ranged from 2 to 7·6%, with heterozygosity restricted again mainly to EST-1. Some alleles were unique to certain geographical regions (including Britain or Spain); others showed significant spatial, and in two British populations examined in successive years, temporal frequency differences. Calculating Nei’s genetic identity (I) and distance (D) coefficients for each population pair mostly gave I>0·8, D<0·2 with overall means (± s.e.m.) of 0·896 ± 0·006 and 0·111 ± 0·006, respectively, which are comparable with geographical population values for other insects. D was poorly correlated with geographical distance, although values were slightly greater (ca. 0·025) for international population comparisons and did not overlap on a principal coordinates plot. The overall population similarity suggests substantial inter-population gene flow; geographical barriers may have restricted movements but seemingly have not led to allopatric race formation. P and values resemble those for many other aphids, but H values are lower than typically found in other insects. Possible causes of this heterozygote deficiency are discussed.
Escherichia coli O157.H7 was found in 10 of 3570 (0·28%) faecal samples from dairy cattle in 5 of 60 herds (8·3%). Several tentative associations with manure handling and feeding management practices on dairy farms were identified. Faecal/urine slurry samples, bulk milk samples, and milk filters from dairy herds were negative for E. coli 0157.H7. E. coli 0157.H7 was also isolated from 10 of 1412 (0·71 %) faecal samples from pastured beef cattle in 4 of 25 (16%) herds. The prevalence of E. coli 0157. H7 excretion in feedlot beef cattle was 2 of 600 (0·33 %). The identification of cattle management practices associated with colonization of cattle by E. coli 0157.H7 suggests the possibility that human E. coli O157.H7 exposure may be reduced by cattle management procedures.
Escherichia coli O157 shedding in 14 cattle herds was
faecal culture at intervals
of approximately 1 month for up to 13 months. The overall prevalence was
faecal samples) and 9 of the 14 herds were detected as positive. Herds
previously (n=5) had a higher prevalence of positive cattle
(median=1·9%) than herds which
had been negative on a previous sampling (n=8, median=0·2%).
Weaned heifers had a
higher prevalence (1·8%) than did unweaned calves (0·9%)
(0·4%). For all herds the
highest prevalence occurred in the summer months, which resulted in most
the positive faecal samples being collected on a minority of sampling
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