641. Carriage and Genetics of Haemophilus influenzae Serotype A (Hia) in Alaska, 2018

Background Haemophilus influenzae serotype a (Hia) is an important cause of infection among Alaska Native children. In 2018, 4 invasive Hia cases (iHia) occurred in an Alaska community. Our response aimed to prevent more iHia and evaluate Hia carriage in the community. Whole genome sequencing (WGS) was performed to compare Hia from iHia patients across Alaska in 2018, and from healthy outbreak community members. Methods We collected oropharyngeal (OP) samples from outbreak community members. Children aged < 10 years and people in close contact with cases (contacts) were offered rifampin prophylaxis. A second set of OP samples was collected 8 weeks later. Isolates from iHia from across the state were collected as part of the state surveillance. Hia was detected by PCR and culture, then characterized by antimicrobial susceptibility and WGS. Results At baseline, contacts had a higher prevalence of Hia carriage than non-contacts (4/27(14.8%) vs 7/364(1.9%), p=0.0043). Eight weeks after rifampin prophylaxis, carriage prevalence did not significantly change among contacts (5/42(11.9%) to 6/25(24%), p=0.18) or non-contacts (7/368(1.9%) to 2/114(1.8%), p=0.47). Phylogenetic analysis of 19 iHia isolates and 15 isolates from healthy outbreak community members, revealed two major clades that differed by an average of 300 core single nucleotide polymorphisms (SNPs). Invasive and carriage isolates from the outbreak community were clustered in one clade, along with 3 non-outbreak iHia isolates. Isolates from this community differed from each other by an average of 1.2 core SNPs. Comparative genomics did not reveal any genetic mutations that distinguished carriage from invasive isolates. Three (20%) community isolates were rifampin-resistant and had a previously unreported mutation in the rpoB gene. Conclusion We found Hia carriage prevalence was highest among persons in contact with iHia cases. Long-term community carriage was not affected by rifampin prophylaxis, possibly due to staggered prophylaxis. In the outbreak community, Hia isolates from carriers were nearly genetically identical to iHia isolates. Overall, iHia isolates from Alaska in 2018 were genetically similar. The mutation conferring rifampin resistance is concerning, as rifampin is used to prophylax contacts of iHia cases. Disclosures All Authors: No reported disclosures