title: Shigella from humans in Thailand during 1993 to 2006: spatial-time trends in species and serotype distribution.
abstract: In Thailand during 1993-2006, a total of 9063 Shigella isolates from different medical centers were serotyped and trends over time and spatial clustering analyzed. Of 3583 cases with age information, 1315 (37%) cases were from children between 0 and 4 years and 684 (19%) from children between 5 and 8 years. Most infections were recorded during 1993-1994 (> 1500 per year), decreasing to < 200 in 2006. The relative species distribution also changed. During 1993-1994, Shigella flexneri accounted for 2241 (65%) of 3474 isolations. This proportion decreased to 64 (36%) of 176 infections in 2006. Most infections occurred during July and August, and fewest in December. S. flexneri clustered around Bangkok, and Shigella sonnei in southern Thailand. Most S. flexneri infections were caused by serotype 2a (1590 of 4035) followed by serotype var X (1249). For both serotypes, a pronounced decrease in the number of isolates occurred over time. A much smaller decrease was observed for serotype 3a isolates. Phase I S. sonnei was initially most common, but shifted gradually over phase I, II, to only phase II. No differences in spatial distribution were found. The three most common S. flexneri serotypes all clustered in, around, and west of Bangkok. Serotypes 2a and 3a also clustered in southern Thailand, whereas var X clustered north and northeast of Bangkok. In conclusion, looking at Shigella species, Thailand changed from being a developing country to a developed country between 1995 and 1996. In addition, major shifts in the types of S. sonnei were observed as were differences in spatial clustering of S. flexneri and S. sonnei and S. flexneri serotypes.
authors.affiliation: Department of Medical Sciences, WHO International Salmonella and Shigella Centre, National Institute of Health, Ministry of Public Health, Bangkok, Thailand.
authors.forename: Aroon
authors.initials: A
authors.lastname: Bangtrakulnonth
authors.forename: Antonio R
authors.initials: AR
authors.lastname: Vieira
authors.forename: Danilo M A
authors.initials: DM
authors.lastname: Lo Fo Wong
authors.forename: Srirat
authors.initials: S
authors.lastname: Pornreongwong
authors.forename: Chaiwat
authors.initials: C
authors.lastname: Pulsrikarn
authors.forename: Pathom
authors.initials: P
authors.lastname: Sawanpanyalert
authors.forename: Rene S
authors.initials: RS
authors.lastname: Hendriksen
authors.forename: Frank M
authors.initials: FM
authors.lastname: Aarestrup
mesh_terms: D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003710:Demography; D019049:Developed Countries; D003906:Developing Countries; D004405:Dysentery, Bacillary / Q000453:epidemiology* / Q000209:etiology / Q000382:microbiology*; D005260:Female; D005506:Food Contamination / Q000032:analysis; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D010802:Phylogeny; D012703:Serotyping; D012760:Shigella / Q000145:classification* / Q000302:isolation & purification*; D012763:Shigella flexneri / Q000145:classification / Q000302:isolation & purification; D012764:Shigella sonnei / Q000145:classification / Q000302:isolation & purification; D013045:Species Specificity; D013785:Thailand / Q000453:epidemiology