Haemophilus Influenzae Serotype A (Hia) Carriage In A Small Alaska Community After A Cluster Of Invasive Hia Disease, 2018

Background. Between May and July 2018, 4 Haemophilus influenzae serotype a (Hia) infections occurred in a remote Alaska community. We performed a public health response to prevent further illness and understand Hia carriage.Methods. We collected oropharyngeal samples community-wide to evaluate baseline carriage. Risk factors were evaluated by interview. We offered prophylactic rifampin to individuals in contact with invasive Hia patients (contacts) and to all children aged <10 years. Oropharyngeal samples were collected again 8 weeks after rifampin distribution. Samples were tested using real-time polymerase chain reaction and culture.Results. At baseline, 4 of 27 (14.8%) contacts and 7 of 364 (1.9%) noncontacts (P < .01) carried Hia. Contacts aged <10 years were more likely to carry Hia at any timepoint (11/18 [61%]) compared to contacts aged >= 10 years (3/34 [8.8%]), noncontacts aged <10 years (2/139 [1.4%]), and noncontacts >= 10 years (6/276 [2.2%]) (P < .001 for all). Hia carriers were clustered in 9 households (7% of total households). At the household level, carriage was associated with households with >= 1 contact (prevalence ratio [PR], 5.6 [95% confidence interval (CI), 1.3-21.6]), crowding (PR, 7.7 [95% CI, 1.1-199.5]), and >= 3 tobacco users (PR, 5.0 [95% CI, 1.219.6]). Elevated carriage prevalence persisted in contacts compared to noncontacts 8 weeks after rifampin distribution (6/25 [24%] contacts, 2/114 [1.8%] noncontacts; P < .001).Conclusions. Hia carriage prevalence was significantly higher among contacts than noncontacts. Rifampin prophylaxis did not result in a reduction of Hia carriage prevalence in this community.