we studied patients admitted to the prince of wales hospital , hong kong special administrative region , who had laboratory - confirmed acute hepatitis e during 2002 2007 . acute hev infection was diagnosed on the basis of clinical manifestations of acute hepatitis , elevation of hepatic parenchymal enzyme levels , and presence of anti - hev immunoglobulin ( ig ) m as determined by an hev igm kit ( biotec laboratories ltd . , suffolk , uk ) . clinical data were retrieved from patients records in the computerized clinical management system of the hospital . hev rna was then amplified from patients stored serum by using a nested reverse transcription pcr ( rt - pcr ) specific for open reading frame ( orf ) 2 with external primers consorf2-s1 ( 5-gacagaattratttcgtcggctgg-3 ) and consorf2-a1 ( 5-cttgttc rtgytggttrtcataatc-3 ) and internal primers consorf2-s2 ( 5-gtygtctcrgccaatggcgagc-3 ) and consorf2-a2 ( 5-gttcrtgytggttrtcataatcctg-3 ) ( 5 ) . positive samples were subjected to another nested rt - pcr targeting orf1 with external primers he5 - 1 ( 5-tcgatgccatggaggccc-3 ) and hevorf1 - 1as ( 5-ggccattgcctccgcaacatc-3 ) and internal primers he5 - 2 ( 5- gccytkgcgaatgctgtgg-3 ) and hevorf1 - 2as ( 5- accatcaaagcagtaagtccg-3 ) ( 6 ) . the orf2 ( 145-bp ) and orf1 ( 364-bp ) pcr products were sequenced , and sequence fragments were aligned by clustalx 2.0 ( 7 ) . phylogenetic trees were constructed by using the neighbor - joining method ( 8) , and rooted phylogenetic trees were generated by using paup * version 4.0b ( 9 ) . bootstrapping values obtained from 1,000 resamplings of the data were performed to assess the robustness of trees ( 10 ) . nucleotide sequence similarity among isolates was analyzed by using the bioedit software ( 12 ) . the sequence data were deposited in genbank under accession nos . fj438395fj438427 and fj438428fj438460 , respectively . nineteen were females ( none pregnant ) 1482 years of age ( median age 57 years , interquartile range [ iqr ] 4374 years ) ; 38 were men 2676 years of age ( median age 52 years , iqr 3867 years ) . no significant difference in age was observed ( p = 0.323 by mann - whitney u test ) . eleven patients were hepatitis b carriers , 1 had cirrhosis , and 1 was a hepatitis c carrier . forty - eight ( 84% ) patients had no history of travel during the prior 6 months . nine ( 16% ) had traveled outside hong kong ( 6 to people s republic of china , 1 to macau , 1 to south korea , 1 to the united states ) 14 weeks before illness onset . the highest liver function levels recorded for the women were serum alanine aminotransferase ( alt ) 2616,500 iu / l ( median 1,280 iu / l , iqr 4348,322 iu / l , reference < 58 serum alkaline phosphatase ( alp ) levels ranged from 111 to 469 iu / l ( median 214 iu / l , iqr 178268 iu / l ) , and total serum bilirubin levels ranged from 10 to 565 mol / l ( median 85 mol / l , iqr 30146 mol / l , reference , < 15 mol / l ) . the highest liver function levels recorded for the men were serum alt 2534,525 iu / l ( median 1,714 iu / l , iqr 1,0432,608 iu / l , reference < 58 iu / l ( median 188 iu / l , iqr 132261 iu / l , reference 35100 iu / l ) , and total serum bilirubin 10544 mol / l ( median 112 mol / l , iqr 72227 mol / l , reference < 15 mol / l ) . thirteen patients had other medical conditions including end - stage renal failure , diabetes , ischemic heart disease , colon cancer , system lupus erythematous , thyroitoxicosis , hepatitis b liver cirrhosis , and previous liver transplantation . patients with a medical condition had significantly higher levels of serum alp ( median 267 iu / l , iqr 861,703 iu / l ) than did those without medical conditions ( median 192 iu / l , iqr 131164 iu / l ; p = 0.03 by mann - whitney u test ) . phylogenetic analyses of the orf2 fragments from 46 patients and orf1 fragments from 33 patients showed complete agreement ( figure ) , with most ( 45 [ 98% ] ) belonging to genotype 4 . the remaining isolate was genotype 3 ( hk14 ) obtained from a woman who had no history of travel . most of the hong kong isolates clustered closely with a swine isolate reported from guangxi province , china ( accession no . furthermore , the orf2 phylogenetic tree showed our isolates were closely related to those reported recently from beijing , china ( accession nos . phylogenetic tree 
     showing the relationship of hepatitis e virus ( hev ) isolates from hong kong . trees were constructed by the neighbor - joining method based on the partial nucleotide sequence of the open reading frame ( orf ) 2 ( a ) and orf1 ( b ) regions of hev samples . bootstrap values for the various branches are shown as percentages of trees obtained from 1,000 resamplings of the data . sequences used for phylogenetic analysis were isolates from genotype 1 : burma ( genbank accession nos . m73218 ; d10330 ) , pakistan ( m80581 ) , india ( x98292 ; x99441 ) , and china ( d11092 ; d11093 ) ; genotype 2 : mexico ( m74506 ) ; genotype 3 : usa ( af060668 ; af060669 ) , japan ( ap003430 ) ; and genotype 4 : china ( ab108537 ; ab197674 ; af082083 ; af082084 ; af082087 ; af082095 ; af082096 ; aj272108 ; eu107466 - 74 ) , japan ( ab074915 ; ab074917 ; ab080547 ; ab091395 ; ab097812 ; ab099347 ; ab161717 - 19 ; ab220971 - 79 ; ab253420 ; ab369688 ; ab369690 ) . branches of swine hev genotype 3 sequences ( ab238522 ; af455784 [ experimentally infected swine ] ) and swine hev genotype 4 sequences ( ay723745 ; dq450072 ; ef570133 ; eu366959 ; eu676172 ) are included in the analysis . accession numbers in boldface are swine isolates . all isolates from the current study have a prefix hk followed by a number in italics . we further analyzed the sequence variation of 32 hev genotype 4 isolates for which orf1 and orf2 sequences were generated in the current study . the nucleotide sequence similarity was 79.9% for the orf1 region ( nt 170448 ) , and 86.4% for orf2 ( nt 64096504 ) . for comparison , the sequence similarity for hev isolates collected elsewhere that had been deposited in genbank was 73.8% for orf1 ( nt 170448 ) and 74.0% for orf2 ( nt 64096504 ) . regions within nt 171221 , 280310 , and 6,4616,495 were most conserved and represented the best targets for primer or probe design . our study showed that most hev cases in hong kong were sporadic and autochthonous . although a substantial proportion ( 21% ) of patients were hepatitis b or c carriers , all diseases had a self - limiting course . this finding could be related to the circulation of relatively mild genotypes 3 and 4 in this locality . the epidemiology of hev in hong kong resembled industrialized countries with a predilection for older adults , rather than older children and young adults as occurs in developing countries . patients with hev infections were older than those with hepatitis a , which peaked in persons 2029 years of age , as reported by chau et al . the distribution of hev genotypes is related to geographic location and the mode of spread ( 2 ) . genotype 3 is widely distributed and has been isolated from humans in north and south america , europe , japan , and the pacific region and in domestic pigs in many countries except in africa . genotype 4 has been isolated from humans in china , japan , taiwan , and vietnam and from domestic pigs , boar , and deer in many countries ( 2,5,6 ) . genotype 4 , the predominant genotype in hong kong , is less virulent ; it is responsible for occasional cases of clinical hepatitis in industrialized countries . a recent study from guangzhou in southern china showed that most ( 39/41 ) hev isolates found there were similar to burmese - like isolates ( genotype 1 ) ( 15 ) . this finding could imply that the poor hygienic conditions required for sustaining the circulation of genotypes 1 and 2 do not exist in hong kong . the sporadic nature , older age of affected patients , and predominance of genotype 4 correspond with the epidemiology in industrialized countries where zoonosis is the major source of infection . public health control should focus on zoonotic , especially swine , foodborne transmission as a source of human hev infection in hong kong .