Chronic hepatitis B infection: A global disease requiring global strategies

T here has been a dramatic decline in the incidence of new hepatitis B virus (HBV) infections in the United States over the last 20 years. This was achieved partly through effective immunization. The immunization strategy in the U.S. has included for approximately the last 20 years the following components: (1) routine vaccination of infants; (2) routine vaccination of adolescents who were not vaccinated as infants; (3) routine screening of pregnant women and appropriate postexposure immunoprophylaxis of infants born to hepatitis B surface antigen (HBsAg)-positive women; and (4) vaccination of adults at increased risk of infection. In addition to widespread vaccination, HBV transmission was reduced in the U.S. by limiting the exposure of susceptible persons to HBV by the following measures: (i) screening of donor blood and plasma derived products for HBsAg and viral inactivation procedures; (ii) adoption of safe sex practices; (iii) availability of needle exchange programs; and (iv) Implementation of universal precautions among laboratory and healthcare workers. These measures have reduced the incidence of new HBV infections in the U.S. and have led to a cohort of children and adolescents growing up with very high rates of immunity against HBV and very low rates of infection. Thus, if the U.S. was a “closed system,” one would expect the prevalence of HBV infection in the U.S. to decline and be practically eradicated in the next few decades. This is unlikely to happen precisely because the U.S. is not a “closed system” due to the great impact of immigration. HBV is a truly global disease with an enormous worldwide reservoir of 350 million infected persons, which far exceeds the worldwide reservoirs of HCV ( 150 million) and human immunodeficiency virus (HIV) ( 34 million). Two billion people, or one-third of the world’s population, are estimated to have been exposed to HBV. Thus, while the incidence of new HBV infections has declined dramatically in the U.S., the prevalence of HBV has not changed much due to a dramatic increase in immigration into the U.S. from endemic (HBsAg-positive in 2%) and hyperendemic (HBsAg positive in 8%) countries over the last 50 years (Fig. 1). While in 1960 there were only 9.7 million foreign-born persons in the U.S. constituting 5.4% of the population, in 2010 there were 40.0 million foreign-born persons constituting 12.9% of the population (Fig. 1A). More important, foreign-born persons from endemic/hyperendemic countries constituted a negligible proportion of all foreign-born persons in 1960. However, by 2010 Asian and African countries with endemic or hyperendemic HBV were the countries of birth of 28% and 4%, respectively, of all foreignborn persons in the U.S. (Fig. 1B-D). Several studies have used estimates of HBV prevalence in the country or region of origin of foreign-born persons living in the U.S. together with estimates of their numbers to calculate how many foreign-born U.S. residents might be expected to have HBV infection. Weinbaum et al. estimated that out of 35,689,467 foreign-born U.S. residents in 2005, 939,416 (or 2.6%) had chronic HBV; Kowdley et al. estimated that out of 38,433,860 foreign-born U.S. residents in 2009, 1,324,693 had chronic HBV in 2009. These calculations critically depend on estimates of HBV infection prevalence in the country of origin, which may be inaccurate, and on the assumption that immigrants to the U.S. have a similar prevalence of HBV as that of their entire country of origin, which may be untrue. Nonetheless, these staggering estimates of foreign-born U.S. residents with HBV far exceed the number of U.S.-born residents with HBV estimated at 229,000-534,000. Thus, foreign-born persons from endemic and hyperendemic countries now constitute the majority of HBV-infected patients in the U.S. Looking at incidence rather than prevalence, and using similar methods based on estimates of HBV in the country of origin, Mitchell Abbreviations: API, Asian/Pacific Islanders; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HBV, hepatitis B virus; HIV, human immunodeficiency virus; USCIS, United States Citizenship and Immigration Service. Address reprint requests to: George N. Ioannou, BMBCh, M.S., Veterans Affairs Puget Sound Health Care System, Gastroenterology, S-111-Gastro, 1660 S. Columbian Way, Seattle, WA 98108. E-mail: georgei@medicine.washington. edu; fax: 206-764-2232. Copyright VC 2013 by the American Association for the Study of Liver Diseases. View this article online at wileyonlinelibrary.com. DOI 10.1002/hep.26516 Potential conflict of interest: Nothing to report.