Comparison of outer membrane protein subtypes of Haemophilus influenzae type b isolates from healthy children in the general population and from diseased patients

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Abstract
Over a 12-month period we obtained throat cultures from 1,448 children less than 5 years of age attending well-child clinics and identified 24 carriers of Haemophilus influenzae type b (1.7%). The outer membrane protein subtypes of the strains from the carriers were compared to the subtypes of isolates from 50 patients with Haemophilus type b disease hospitalized in St. Louis, Mo., during the same period (1981 to 1982), and the latter were compared to the subtypes of isolates from 51 patients hospitalized between 1977 and 1980. There were no significant differences in the frequencies of the five most common subtypes (1L, 1H, 2L, 2H, and 3L), comparing isolates from the carriers to those from the patients. However, 5 of the 24 throat isolates had the unusual 13L subtype compared with only 1 of the 50 invasive isolates (P = 0.02). The lower frequency of 13L strains among the invasive isolates suggests that type b isolates with this subtype may be less pathogenic than type b isolates with other subtypes. Subtype 2L strains accounted for only 2% of recent cerebrospinal fluid or blood isolates, compared with 22% of those from 1977 to 1980 (P = 0.02). Subtype 1H and 3L strains together accounted for 73%, compared with 47% of the earlier ones (P = 0.02). Thus, temporal shifts may also occur in the subtype distribution of Haemophilus type b strains causing invasive disease in a community.