1604. Response to a Cluster of Haemophilus influenzae Serotype A Cases in a Small Alaska Community, 2018

BACKGROUND: Between May and July 2018, four invasive cases of Haemophilus influenzae type a (Hia) occurred in a remote Alaska community. A public health response was performed to prevent further illness and to understand local Hia transmission. METHODS: The team identified close contacts of the Hia patients, collected oropharyngeal (OP) swabs and provided prophylactic rifampin. Close contacts were persons who spent ≥4 hours with a Hia patient for ≥ 5 of the 7 days preceding hospitalization. Five days later, OP swabs were collected community-wide and prophylactic rifampin was offered to community members aged <10 years. Eight weeks later, OP swabs were collected from all willing community members. Samples were tested using PCR and culture to identify Hi carriage. RESULTS: No Hia cases occurred in this community after the response. The pretreatment carriage prevalence is shown in Figure 1. There was a significant difference in prevalence of Hia carriage between contacts (4/27, 14.8%) and non-contacts (7/364, 1.9%) (P = 0.0043). Contacts aged <10 years were significantly more likely to carry Hia compared with contacts aged ≥10 years (11/18 [61.1%] vs. 3/34 [8.8%], P = 0.0001). The case households had the highest proportion of individuals who carried Hia at any time, with 54%–60% of individuals in three case households carrying Hia at least once. Hia carriage was eliminated in two carriers who completed treatment and were tested immediately after rifampin prophylaxis. Testing 8 weeks later found that the prevalence of carriage did not significantly change in the contacts (5/42 [11.9%] to 6/25 [24%], P = 0.18) or the non-contacts (7/368 [1.9%] to 2/114 [1.8%], P = 0.47). CONCLUSION: Children aged <10 years who had close contact with the Hia patients were the most likely to carry Hia. These findings suggest that people who do not have close contact do not benefit from prophylaxis as they have very low Hia carriage. While rifampin prophylaxis eliminated carriage of Hia in the short term, carriage prevalence did not change in the long term. Further research is needed to understand why contacts have such a high prevalence of carriage even after receiving appropriate prophylactic medication. [Image: see text] DISCLOSURES: All authors: No reported disclosures.