Haemophilus influenzae serotype a (Hia) carriage in a small Alaska community after a cluster of invasive Hia disease, 2018.

Nolen, Leisha D; Tiffany, Amanda; DeByle, Carolynn; Bruden, Dana; Thompson, Gail; Reasonover, Alisa; Hurlburt, Debby; Mosites, Emily; Simons, Brenna C; Klejka, Joe; Castrodale, Louisa; McLaughlin, Joseph; Bruce, Michael G

BACKGROUND Between May and July 2018, four invasive Haemophilus influenzae serotype a (iHia) infections occurred in a remote Alaska community. We performed a public health response to prevent further illness and understand Hia carriage in the community. METHODS We collected oropharyngeal (OP) samples community-wide from untreated individuals to evaluate baseline carriage. Risk factor data was collected by interview. To prevent additional illness, we offered prophylactic rifampin to individuals in contact with iHia patients (contacts) and to all children aged <10 years. OP samples were collected again eight weeks post-rifampin distribution. Samples were tested using real-time PCR and culture. RESULTS At baseline, Hia was carried by 4/27 (14.8%) contacts and 7/364 (1.9%) non-contacts (p<0.01). Contacts aged <10 years were more likely to carry Hia at any timepoint (11/18, 61%) than contacts aged ≥10 years (3/34, 8.8%) or non-contacts aged <10 years (2/139, 1.4%) and ≥10 years (6/276, 2.2%)(p<0.001 for all). Hia carriers were clustered in nine households (7% of total households). At the household level, carriage was associated with households with ≥1 contact (PR=5.6, CI:1.3-21.6), crowding (PR=7.7, CI:1.1-199.5) and ≥3 tobacco users (PR=5.0, CI:1.2-19.6). Sixty-six percent (40/61) of contacts and 90% (111/124) of non-contacts aged <10 years received rifampin. Elevated carriage prevalence persisted in contacts when retested eight weeks after rifampin distribution (contacts 6/25 (24%), non-contacts 2/114 (1.8%), p<0.001). CONCLUSIONS Hia carriage prevalence was significantly higher among people who had contact with iHia patients than the general community. Rifampin prophylaxis did not result in a reduction of Hia carriage prevalence in this community.