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SAN FRANCISCO -- The epidemiology of hepatitis A infections may be experiencing a recent dramatic shift from common-source infections to outbreaks, a researcher said here.

A steadily increasing trend of outbreak-associated infections from 2012-2016 shot up dramatically, when a combination of 2017 data found that 43% of hepatitis A infections were outbreak-associated infections, reported Monique Foster, MD, of the CDC in Atlanta.

In a , she noted how previously, large community outbreaks of hepatitis A were associated with asymptomatic children, who would then pass the virus onto adults who would then infect other adults. But that has changed with the that all children receive the hepatitis A vaccine.

Foster added that a large population of adults -- who are more likely to experience severe disease and adverse outcomes -- are not immune to hepatitis A virus, and that uptake of the vaccine among high-risk adults, such as travelers, men who have sex with men, and persons who use drugs, has been low, she said.

"There is no universal recommendation for hepatitis A vaccination in adults. The outbreaks in the last 2 years highlighted that vulnerable populations can be better protected," she said in a presentation at the ID Week, with joint sponsorship by the (IDSA), the (PIDS), the (SHEA), and the (HIVMA).

“In many ways, the changing epidemiology of hepatitis A has been riding the wave of increased homelessness and the opioid crisis. So the change really reflects these changing social conditions,” Stephen Morse, PhD, of the Columbia University Mailman School of Public Health in New York City, told 木瓜直播.

“Detroit, San Diego, places in Kentucky, Tennessee, West Virginia, Arkansas, Missouri, and others, almost all linked to the same causes (and often the same virus strain, just as we see interstate movement with the opioid users),” said Morse, who was not involved with the research, adding that “immunization is the mainstay” strategy against hepatitis A.

“Many health departments have been making tremendous efforts to reach out to these populations,” he said. “In California, for example, over 123,000 doses of vaccine have been distributed since November 2016, and the state Department of Public Health believes the problem is now mostly under control.”

Recently, the CDC Advisory Committee on Immunization Practices (ACIP) recommended the use of hepatitis A vaccine in outbreaks, and the FDA recently approved a new formulation of hepatitis A immunoglobulin, which is recommended for certain populations as post-exposure prophylaxis.

Given the recent outbreaks, which Foster characterized as having "high hospitalization and case mortality rates," researchers sought to examine if the epidemiology of the disease has changed by looking at two 5 year time-periods -- 2007-2011 and 2012-2016, as reported to the (NNDSS).

The 2017 data was a combination of NNDSS data and "cases reported directly to the CDC hepatitis outbreak response team during 2017," and excluded data from four states that were reporting directly to the latter, to avoid double-counting.

When examining the two 5-year time periods only, the total number of reported hepatitis A infections declined (10,619 in 2007-2011 vs 8,419 in 2012-2016), although there was a statistically significant increase in the median age of these cases (36 to 42, respectively). There was no difference between the sexes, with about half of cases among men. Examining race, cases were 53% to 59% white, though the number of "unknown" race decreased in the most recent time period (28% to 19%, respectively).

In these time periods, the number of infections associated with outbreaks climbed from 5% to 8%, respectively, with a dramatic increase in median age (28 to 41). Of outbreak-associated infections where clinical data was reported, hospitalizations rose from 39% to 58%.

However, these results shifted dramatically when factoring in preliminary 2017 data. Last year, there were 3,421 reported hepatitis A infections, with a median age of 40. Two-thirds of 2017 cases were men, and over two-thirds were white.

Moreover, the portion of outbreak-associated infections climbed to 43% of total infections based on preliminary 2017 data. Of these infections where clinical data were reported, 99% were hospitalized, and the death rate jumped from 0.7% in 2012-2016 to 4%.

The authors concluded that previously hepatitis A outbreaks were "infrequent and typically associated with a common source," outbreak-linked cases, hospitalizations and deaths were on the rise. However, Foster cautioned that "clinical outcomes are difficult to interpret from NNDSS alone."

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