The K1 serotype of K. pneumoniae was uncommon among clinical isolates before the 1990s . However, K1 serotype infection has been more widespread in Asian countries despite a recently reported increasing role of K. pneumoniae in liver abscess in the United States [15, 16]. The reason for the epidemiological changes and global differences observed remains unexplained. In this study focusing on Chinese in different Asian regions, a substantial proportion of serotype K1/K2 K. pneumoniae strains colonizing the intestine, except for Thailand and Vietnam, suggest that Chinese ethnicity itself might be a major factor predisposing to intestinal colonization by these strains. It also corresponds to the prevalence of liver abscess in Asian countries. The differences in socioeconomic factors, dietary practices, environmental exposure, living conditions, and the use of antimicrobial agents might also have a potential role for the geographic differences in seroepidemiology among K. pneumoniae isolates.
In our previous study in Taiwan, 77.6% of K. pneumoniae liver abscesses were caused by serotype K1 or K2 isolates . A previous study has found that K. pneumoniae isolates from patients with liver abscesses in Singapore and Taiwan have similar characteristics, such as genomic heterogeneity and prevalence of virulence factors . The prevalence of serotypes K1/K2 K. pneumoniae colonizing the intestinal tract in Taiwan is similar to that in Singapore. The prevalence of serotype K1/K2 K. pneumoniae isolates colonizing the intestine may contribute to invasive liver abscess syndrome in Taiwan and Singapore.
In Hong Kong, serotype K1 isolates from liver abscess specimens were studied, but the associated clinical details of the patients were not available . A recent study from Japan has reported familial spread of a K1 clone of K. pneumoniae causing primary liver abscess . In another study from Malaysia , K. pneumoniae rarely caused liver abscess and isolates were not serotyped . In a recent study in China, K. pneumoniae was the prevalent pathogen in liver abscess but the serotypes of isolates were unavailable . Further research focusing on serotype of K. pneumoniae isolates in these countries might clarify the relation between colonization and infection. K. pneumoniae-associated liver abscess caused by serotype K1 has never been reported in Thailand or Vietnam. Interestingly, we did not find any serotype K1 K. pneumoniae isolate from stools in the two countries.
In the present study, there was no major clonal cluster of serotype K1 isolates in Asian countries. Although one previous study of the molecular epidemiology of liver abscess in Taiwan identified a major cluster of K. pneumoniae isolates causing liver abscess , subsequent studies with the methods of ribotyping and PFGE have shown that K. pneumoniae-related liver abscesses are not caused by a clonally-spread strain [3, 21, 22]. Another study has further demonstrated that K. pneumoniae isolates causing liver abscess are not clonal in either Singapore or Taiwan . Turton et al. firstly reported that the prevalence of strain ST23 in liver abscesses in Taiwan was high and that the strains were clonally related . In the current study, we screened for strain CC23 representatives by detection of allS by PCR  and found that isolates carrying allS were also predominant in serotype K1 K. pneumoniae present in healthy adult stools. However, isolates carrying allS from stools were not related by PFGE, indicating that a geographic difference might account for the diversity.
An important limitation of this study was the lack of data regarding Chinese residents in Korea. Invasive liver abscess caused by K. pneumoniae K1 serotype has been emerging in Korea [5, 24]. A further study of the serotype and genetic relatedness of K. pneumoniae isolates colonizing the intestine in Korea may elucidate the epidemiology of emerging disease caused by K1 K. pneumoniae in Asia. Future investigation of K. pneumoniae from stools in Western countries is also needed to delineate the global epidemiology and the relation with K. pneumoniae liver abscess.