January 18, 2006
JAMA: Vol. 295 No. 3
To the Editor: In their study of hepatitis A immunization, Dr Dagan and colleagues1 described a remarkable decline in the rate of hepatitis A following a universal toddlers-only immunization program in Israel in 1999. In the same issue of JAMA, Dr Wasley and colleagues2 reported a reduction in the incidence of hepatitis A in the United States to historic lows after the implementation of childhood vaccination programs in several states. Both studies described a substantial reduction in hepatitis rates not only among children but also in adults. Wasley et al suggested that in the absence of transmission among children, transmission among some groups of adults (which is usually via the fecal-oral route, through close person-to-person contact, or by ingesting contaminated food or water3) may still be sustained.

Several investigators have reported the increase of enteric diseases in general4 and hepatitis A in particular5 during the summer when the virus may persist for a longer time in the environment. The recent epidemiological changes imply that current cases are increasingly associated with different routes or sources of infection, but this could not be detected in the data presented by Wasley et al2 and Dagan et al.1 However, it might be addressed in part by examining the seasonality patterns of hepatitis A before and after the immunization campaigns.
Gabriel Chodick, PhD
hodik_g@mac.org.il
Varda Shalev, MD
Maccabi Healthcare Services
Tel Aviv, Israel
In Reply: In the United States, the dramatic declines in the incidence of hepatitis A among children and their close contacts have resulted in changes in the epidemiologic profile of this disease, including a shift in the distribution of cases by age, race, and region, as well as changes in the frequency of potential sources of infection as reported in national surveillance data.
The large community-wide outbreaks that were driven by infections among children and transmission within households and extended family settings, previously accounting for the majority of cases in the United States, have become rare. A declining proportion of cases report sexual or household contact with another case or potential exposure through attendance in child day care.1 As sources of local, community-based transmission have been reduced, an increasing proportion of the cases that continue to occur are in high-risk groups such as international travelers.
Historically, there has not been any detectable seasonality in the incidence of hepatitis A in the United States. Therefore, looking for deviations from a seasonal pattern is unlikely to provide any additional information for evaluating the impact of hepatitis A vaccination here.
Financial Disclosures: None reported.
These letters were shared with Dr Dagan, who declined to reply.–ED
Annemarie Wasley, ScD
awasley@cdc.gov
Beth Bell, MD, MPH
Division of Viral Hepatitis
Centers for Disease Control and Prevention
Atlanta, Ga