Viral Hepatitis and Liver Cancer on the Island of Guam

Guam is the southernmost island of the Mariana Archipelago in the Western Pacific ocean. It is the largest (approximately 212 sq. miles), tallest (1,332 feet), and most populous (159,358 in 2010) island of Micronesia (Cox et al., 1926; Carano, 1968; Guam State Data Center, 2012). After the liberation of Guam from Japanese occupation in 1944, the island experienced a rapid increase of in-migration by Filipinos and Asians, principally as contract workers, Micronesians from neighbor islands seeking jobs and educational opportunities not available at home, and Caucasians as teachers or other government employees and in the military. Today the island is populated principally by indigenous Chamorros, including part-Chamorro (42.15%), Filipinos (26.31%), Micronesians other than Chamorros (7.17%), Caucasians (6.79%), Asians (6.20%), and Others (11.38%) (Guam State Data Center, 2012). The Guam Cancer Registry was established by legislative authority in 1998 and today is operated by the University of Guam under a Memorandum of Agreement with the Guam Department of Public Health and Social Services (Haddock, 2013). A registry of viral hepatitis cases was created by reviewing communicable disease reports dating back to 1970. New cases are added to the registry from clinical or laboratory reports if they have not been previously listed. It is recognized that most such cases do not represent recent infections but may have been acquired at a much younger age when typically vague symptoms did not result in a clinical diagnosis


Introduction
Guam is the southernmost island of the Mariana Archipelago in the Western Pacific ocean.It is the largest (approximately 212 sq.miles), tallest (1,332 feet), and most populous (159,358 in 2010) island of Micronesia (Cox et al., 1926;Carano, 1968;Guam State Data Center, 2012).After the liberation of Guam from Japanese occupation in 1944, the island experienced a rapid increase of in-migration by Filipinos and Asians, principally as contract workers, Micronesians from neighbor islands seeking jobs and educational opportunities not available at home, and Caucasians as teachers or other government employees and in the military.Today the island is populated principally by indigenous Chamorros, including part-Chamorro (42.15%),Filipinos (26.31%),Micronesians other than Chamorros (7.17%), Caucasians (6.79%), Asians (6.20%), and Others (11.38%) (Guam State Data Center, 2012).
The Guam Cancer Registry was established by legislative authority in 1998 and today is operated by the University of Guam under a Memorandum of Agreement with the Guam Department of Public Health and Social Services (Haddock, 2013) combined to compare the prevalence of viral hepatitis and the incidence of liver cancer among the ethnic groups represented on Guam.The IBM SPSS software (Version 20) was used for statistical analyses.Descriptive statistics were performed to describe the age, gender, and ethnic characteristics of the hepatitis cases in this population.The Pearson's chi-square test was used to compare the observed and expected counts of hepatitis cases, as wells as liver cancer cases across the ethnic groups.The groups identified were Asian, Chamorro, Filipino, Micronesian, and White.The Chamorros included those from Guam and the Commonwealth of the Northern Mariana Islands.The Micronesian group included Chuukese, Kosraean, Marshallese, Palauan, Pohnpeian, and Yapese.The Asian group included Chinese, Japanese, Korean, Vietnamese, and Other Asian.

Results
The mean age of the 3,437 hepatitis cases on Guam from 1970 to 2012 was 40.7±16.7 years old (Table 1).There were slightly more males than females.Approximately one-third (34.7%) of the cases were Chamorros.The ethnicity for about one-fifth of the cases was identified as Other or Unknown (21.2%), and thus these cases were excluded from further analyses.
Based on the Pearson chi-square test, the difference in proportion of hepatitis cases among the ethnic groups studied was statistically significant, χ 2 =676.3,df=8, p=0.000 (Table 2).The Chamorros had the most cases of hepatitis A (5.2%) and Hepatitis C (19.6%), whereas the Micronesians had the highest cases of Hepatitis B (23.4%).The difference in proportion of liver cancer cases among Guam ethnic groups was also statistically significant, χ 2 =22.3, df=4, p=0.000.Hepatitis C was the type of hepatitis most common among liver cancer cases (63.3% of viral hepatitis-associated liver cancer cases) (Table 3).

Discussion
Causes for the striking ethnic differences in the prevalence of hepatitis A, B, and C are not known and clarification awaits further study.Ethnic differences in risk factors such as household crowding, food preparation techniques, unprotected sex, intravenous drug use, and infant care practices may play important roles.In addition, more than 20% of the hepatitis registry cases were excluded from ethnicity analyses because the ethnic group they represented was too small for analysis or the ethnicity was unknown.However, our data are in line with the published figures for liver cancer incidence and mortality, with highest numbers for Micronesians followed by Chamorro populations (Haddock et al., 2006;2009).It should also be noted that rates may be rising (Moore et al., 2010).
Acute hepatitis A is now rare on Guam.A policy of requiring all food handlers working in eating and drinking establishments to attend a course on food sanitation initiated in 1975 is believed to have contributed to this improvement.The last known outbreak of hepatitis A occurred in 1972 when 311 cases were reported.The highest incidence that year was in a village which had experienced a major sewage system failure and construction of a new sewage system aborted the outbreak (Haddock, 2010).
It is anticipated that the prevalence of hepatitis B among Guam residents will gradually decrease in the coming years due to a policy initiated in 1988 of providing hepatitis B vaccine to all infants born on Guam.In addition, as a "catch-up" effort, vaccination was offered to all children up to 6 years of age who had not been previously vaccinated (Haddock, 2010).Reducing the prevalence of hepatitis C will be more problematic and control of this disease may be tied to promoting changes in sexual activity or IV drug abuse.
In conclusion, infections of viral hepatitis are an important cause of liver cancer.Studies such as the present one may provide the information necessary to establish targeted programs (infant vaccination in the case of hepatitis B, for example) that will lessen the impact of liver cancer in future generations.

Table 2 . Guam Hepatitis and Liver Cancer Cases of Known Ethnicity, 1970-2012
Based on the Pearson chi-square test, the difference in proportion of hepatitis cases among the ethnic groups is statistically significant, c2=676.3,df=8, p=0.000.The difference in proportion of liver cancer cases among the ethnic groups is statistically significant, c2=22.3,df=4, p=0.000

Table 3 . Liver Cancer Cases by Associated Type of Hepatitis Virus
Includes cases excluded from Table2because ethnicity was unknown or insuffcient for statictical analysis *