BOSTON – A small but concerning recent surge in cases of invasive infection with Haemophilus influenzae serotype a among Native Alaskan children appears to be an "emerging" infection, reported epidemiologists from the Centers for Disease Control and Prevention.

CDC epidemiologists first identified an Alaskan invasive infection by H. influenzae serotype a (Hia) in 2002, and by mid-October 2011 the tally stood at 27 cases in children younger than 5 years old and is still rising, with 13 of the cases clustered in 2010 and 2011, Dr. Michael Bruce said at the annual meeting of the Infectious Diseases Society of America.

Most of the cases have been in children younger than 5 years old, in Alaskan Native children, and most also have been clustered in a specific region of western Alaska. Over the past 2 years, the Hia incidence rate among all Alaskan Native children younger than 5 years old has been 15.4 cases per 100,000, and among these children specifically in the western area, the rate has approached about 200 cases per 100,0000, "comparable to Haemophilus influenzae type b [Hib] in the pre-vaccine era," he said.

"It’s alarming to us that we have this many cases" in 2010 and 2011, he said in an interview. "It is particularly alarming because these children are quite ill. Their symptoms are very similar to what we saw in the past with Hib." The most common presentation of invasive disease has been meningitis in 41% of cases, followed by pneumonia with bacteremia in 26%, and septic arthritis in 22%. Hospitalization was required for 89% of the 27 cases he reviewed since 2002, and two children died, as well as a third death that occurred in a recent case not included in this series, he said.

"This is a serious disease, similar to Hib," said Dr. Bruce, epidemiology team leader in the Artic Investigations Program of the CDC in Anchorage. But, "I don’t think these [Hia cases] are temporally related to use of the Hib vaccine," which virtually eliminated Hib as a cause of invasive infections since its introduction 20 years ago.

Most of the cases have been in children younger than 5 years old, in Alaskan Native children, and most also have been clustered in a specific region of western Alaska.

The 27 invasive Hia cases Dr. Bruce reviewed since it first appeared in children younger than 5 years in 2002 had an average age of 0.7 years old, with a range of 4 months to 2.4 years old, and with 63% of the cases in boys. A total of 25 of the 27 cases (93%) were in Alaskan Native children, and 93% of the cases had been appropriately vaccinated for Hib. In all, 23 of the 27 cases (85%) occurred in western Alaska.

The CDC has no recommendations for treating non-serotype b invasive H. influenzae infections, nor does it have a recommended regimen for prophylactic treatment of close contacts of index cases. Physicians in Alaska have generally been treating invasive Hia infections as they would invasive infections by Hib, and roughly half of the Alaskan physicians who have managed the invasive Hia cases have dispensed preventive antibiotics to close contacts following the old Hib recommendations. So far, epidemiologic investigations in Alaska failed to identify any episodes of secondary Hia infections transmitted from an identified index case, Dr. Bruce said.