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The rate of hepatitis A infection in the United States is the lowest it has been in the nation's history, at 1.3 cases per 100,000, according to the latest study by the Centres for Disease Control and Prevention.
Since vaccines proliferated in the last decade, the highest risk for infection is now international travel, the CDC researchers reported in the November 8 issue of Archives of Internal Medicine. Vaccines have been universal for children since 2006 and the CDC researchers recommend vaccination for all others prior to international travel.
"Before vaccination, outbreaks were common, whereas in our study, they were quite rare," Dr Monina Klevens at the CDC's Division of Viral Hepatitis, who led the research, told.
Lower infection rate
The infection rate has dropped from 14 per 100,000 in the 1990s before vaccination became widespread.
"Universal childhood vaccination appears to have changed the entire epidemiology of HAV infection from an outbreak-associated disease to sporadic cases associated largely with international travel," Drs Karin Andersson and Lawrence Friedman write in a commentary in the same journal.
Dr Klevens' team studied the records of nearly 30 million people documented in health departments in six sites in five states from 2005 to 2007. Among those, they found 1156 cases of acute hepatitis A. Most were aged 15-39, lived in urban areas (a range of 77%-100% among the sites) and about half of the cases tended to be male (range, 49%-55%) and white (range, 20%-77%).
The findings
Of the 1156 cases reported, 529 (46%) were linked to travel in general and 476 (41%) were linked to international travel. Also, 217 (19%) cases were linked to exposure to an international traveller, 52 (4.5%) of whom were exposed to a traveller but didn't travel themselves.
Other reported risk factors were exposure to an infected person (15%), being an employee or child in a daycare centre (7.6%), a common source outbreak (7.2%), illegal drug use (4.3%), and men who have sex with men (3.9%). In 421 cases (36%), the case denied all the above risk factors.
"In about a third of the cases we studied, we did not have information on how the individuals became infected," Dr Klevens said. "If doctors vaccinate their patients that are at risk for hepatitis A, those patients could be protected regardless of how they might be exposed to the virus." (Reuters Health / November 2010)
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