Invasive disease due to nontypeable Haemophilus influenzae among children in Arkansas

Abstract

In this study, we reviewed cases of invasive disease due to nontypeable Haemophilus influenzae among children hospitalized at Arkansas Children's Hospital from 1993 to 2001. A total of 28 cases were examined, including 21 associated with bacteremia and 4 associated with meningitis. Of the patients examined, 86% were </=4 years of age, and 68% had underlying medical conditions. Characterization of the bacterial isolates by multilocus sequence type genotyping revealed significant overall genetic diversity, similar to the diversity in the general population structure for nontypeable H. influenzae. However, four separate pairs of isolates were closely related genetically, a relationship confirmed by pulsed-field gel electrophoresis and Southern hybridization studies using probes for the major H. influenzae adhesin genes. These results suggest that selected strains of nontypeable H. influenzae may have more invasive potential, especially in young children and patients with underlying medical conditions. At this point, the specific factors that contribute to enhanced virulence remain unclear.

FIG. 1.

Restriction digest patterns of invasive isolates of nontypeable H. influenzae. High-molecular-weight DNA from four pairs of nontypeable H. influenzae isolates that shared identical alleles at five loci tested was digested with SmaI, and restriction fragments were separated by PFGE. Lambda ladder molecular weight standards (lanes 1 and 10) and restriction fragments of strains 800 (lane 2) 788 (lane 3), 773 (lane 4), 796 (lane 5), 767 (lane 6), 794 (lane 7), 769 (lane 8), and 795 (lane 9) are shown. Strains 800 and 788, 773 and 796, 767 and 794, and 769 and 795 share identical or highly similar restriction digest patterns.