Association between cross-reacting Escherichia coli K100 and disease caused by Haemophilus influenzae type b

An unexpected association between Haemophilus influenzae type b (HIB) disease and simultaneous intestinal colonization with cross-reacting Escherichia coli K100 strains is reported. E. coli K100 were found in 18 of 92 (19.5%) HIB patients, compared with 2.5% in healthy individuals of comparable age and in none of 21 patients with meningitis caused by other bacteria. There was no difference in disease outcome, serum antibodies, and circulating HIB antigen between the E. coli K100-positive and -negative HIB patients. Possible explanations and implications of this association are discussed.